7 Oxygen, sulfur, selenium and tellurium

P. F. Kelly

Department of Chemistry, Loughborough University, Loughborough, UKLE11 3TU

1 Introduction

This review highlights new developments in the chemistry of the Group 16 elements(the chalcogens) reported during 1999. As in previous years, results that demonstratenovelty of product or synthetic approach as their main feature have beenemphasised. In addition, the products reported have been limited to those in pos-session of a discrete molecular structure, thus highlighting the extraordinary abilityof these elements (sulfur, selenium and tellurium in particular) to contribute to novelcluster arrangements.

2 Sulfur, selenium and tellurium

As with other years we start by looking at the ability of the heavier chalcogens toform compounds with a vast range of other p-block elements, and do so by workingfrom left to right across the periodic table starting with Group 13. The selenoboratesRb8[B12(BSe3)6], Cs4Hg2[B12(BSe3)6] and Rb4Hg2[B12(BSe3)6] have been shown toform from the metal selenides, boron and selenium at 700 �C.1 These new speciescontain B12 icosahedra saturated with six trigonal planar BSe3 moieties acting inbidentate fashion (thus forming a closo-dodecaborate anion). A new galliumchalcogenide anion, [Ga3Se7(en)]

3ÿ, forms from the elements plus en at 130 �C;its structure is built up from bicycles generated fromGa(en)Se3 tetrahedra connectedvia Se corners into linear chains.2

Among carbon-based systems of note are C120OS and a series oftellurocarboxylates. The former results from the reaction of C120O with sulfur at230 �C for a day and appears to be the ¢rst sulfur-bearing C60 derivative (it issuggested that it contains a thiophene linkage between the two fullerenes).3 Thetellurium species have the general formula M[RC(O)Te] (M � K or Na) and formwhen acyl chlorides are treated with alkali metal tellurides.4 They are yellow tored solids or oils with the aromatic derivatives markedly more air stable thanthe aliphatic analogues; as might be expected they react with organic halides to giveproducts of the type RC(O)TeR0. A new coordination mode for the well known

DOI: 10.1039/b002864i Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134 121

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online / Journal Homepage / Table of Contents for this issue

[SCN]ÿ ion has been noted in the double salts AgSCN�2AgNO3 andAgSCN�AgClO4.

5 Both contain SCN binding in a m5-mode, i.e. with sulfur boundto three silver atoms and nitrogen to two, generating 2- or 3-D networks. Movingon to heavier Group 14 elements, both SiS2

6 and F2SiS7 have been isolated in

low temperature matrices. The former (from reaction of SiS with Si atoms) wascharacterised by Raman spectroscopy in a methane matrix while the latter (fromthe £ash vacuum pyrolysis of (F3Si)2S at 500 �C followed by condensation ontoAr) shows IR characteristics consistent with a C2v symmetry. K6Sn2Se6 1 (fromreaction of the elements at 900 �C) provides only the second example of a fullycharacterised hexaselenostannate(III) system.8 As expected it contains two SnSe3units bridged by a Sn^Sn bond of length 2.78 Ð. A more complicated structureis seen in the [AuSn2Te6]

3ÿ anion 2, which forms when the alloy K4AuSn2Sb2Te11is extracted with en.9 It actually provides the ¢rst example of the Sn2Te6 ligand withina ternary Zintl ion. Finally in this area a range of heterocyclic adamantanes of thetype [(RSn)4E6] (E � O, S or Se) have been reported to form from the reactionof organotin halides with Na2E. For example, (ttsm)SnBr3 reacts with Na2S at roomtemperature in liquid ammonia to give [(ttsm)Sn4S6] as a yellow material in 75%yield. X-ray crystallography con¢rmed the adamantane core.10

Over the years the combinations of chalcogens with Group 15 elements has beenone of the more fruitful areas of main group research and this shows no sign ofabating. Examples of nitrogen-containing systems from last year include S2(NSO)2,which forms [together with smaller amounts of Sx(NSO)2 (x � 3, 4 or 5)] whenS2Cl2 reacts with Me3SiNSO.11 Its reactions are dominated by a tendency todisproportionate to S(NSO)2 and sulfur while hydrolysis produces [NH4][S4O6].An extensive survey of the templating effect of Li� cations on the crystallisationof diazasulfates has identi¢ed a range of bonding modes,12 while a redeterminationof the structure of the potassium salt of [O3SN(O)NO]2ÿ (from the reaction ofNO with sul¢te) has revealed a £attened tetrahedral geometry at the sulfur.13 Cal-culations performed alongside the latter work suggest that the reaction proceedsvia a two-step mechanism in which the ¢rst NO binds to S through nitrogen andis then activated towards the second NO attack; such results may have implicationsfor the modelling of nitrite reductase, Wacker catalysis, etc. Among S^N^C com-pounds reported we ¢nd the hybrid cyanuric^sulfanuric ring Cl3C2N3S(O) (which

122 Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online

forms from the reaction of cyclo-Cl3C2N3S with KMnO4/CuSO4)14 and dis-

ubstituted thiadiazoles of the type 3,5-R2CNCNS.15 In the former case, substitutionof the chlorides by CF3CH2O groups leads to a product which undergoes novel O!N migration during thermolysis at 175�C; the latter work also identi¢ed an unusualcation 3 bearing the ¢rst example of the four-membered trithietanylium ring,R^CSSS. Dithiadiazolyl systems have yielded much in the way of interesting resultsover the years and recent work has added to this by performing detailed magneticstudies of the p-BrC6F4CNSSN radical.16 It is a monomer in the solid state andexhibits paramagnetic behaviour with antiferromagnetic interactions at high tem-perature and weaker interactions at lower temperatures. Thus it is only the seconddithiadiazolyl radical to retain paramagnetism in the solid state. Finally, a rangeof azole tri£uoromethylsulfurdi£uorides have been prepared in 30^40% yield.17

Introducing heavier chalcogens into such systems has always proved something ofa challenge. A signi¢cant breakthrough in this area has come with the preparation ofa diselenated analogue of S4N4. 1,5-Se2S2N4 is the brown red product of the reactionof either [(Me3Si)2N]2S with SeCl4 (in CS2 at ÿ70 �C) or [(Me3Si)2N]2Se withSCl2/SO2Cl2 (same temperature in CH2Cl2) and has been characterised byNMR and Raman spectroscopy.18 Attempts to con¢rm the structure by X-raycrystallography were hampered by disorder problems. Moving further down thegroup, a number of Te^N systems have been reported by Chivers et al. The reactionsof the dimeric tellurium diimide [ButNTe(m-NBut)2TeNBut] with metal salts19 andwith tellurium halides20 have been reported. In the ¢rst case a very different ligandbehaviour towards Cu(I) is observed compared to that with Ag(I); in the copperproduct (of formula [Cu2L3]

2�) the copper atoms bridge trans and cis isomers ofthe ligand while silver links two trans ligands in its product dinuclear [Ag2L2]

2�.Both were isolated as the tri£ate salts (dark red for Cu, orange for Ag). Withtellurium halides, products of the type [ButNTe(m-NBut)2TeX2] (X � Cl) or[ButNTeX2]n (X � Cl or Br) form depending upon reaction ratios. The structureof [ButNTeCl2]n, a golden^yellow powder, shows hexameric units in which three[ButNTeCl2]2 dimers are linked by bridging chlorides; weak Te � � � Cl interactionsproduce an overall polymeric array. Finally, the ¢rst homoleptic complexes ofthe tripodal [Te(NBut)3]

2ÿ anion have been formed (coordinated to Bi and Sb).21

Metal complexes of chalcogen^nitrogen species continue to be of importance.Thus last year saw the formation of A-frame adducts of the general formula[Pd2Cl2(dppm)2(m-NSO2R)] bearing six different R groups ranging from phenylto ferrocenyl.22 The arylsulfonylnitrene ligands in such complexes show short

Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134 123

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online

N^S distances (1.54^1.57 Ð) indicating a strong double bond character. The ¢rstexample of a metal-assisted reaction of a sul¢mide with a nitrile has beendemonstrated.23 Thus when Ph2SNH reacts with PtCl2(MeCN)2 the product 4 con-tains the bidentate Ph2SNC(Me)NH ligand. This product is also notable in thatit contains the ¢rst example of sul¢mide binding to metal through the sulfur andthat the resulting MSNCN metallocycle is in fact surprisingly rare. Of the metalsstudied thus far Pt appears to be the only one capable of affecting such a reaction.

Phosphorus sul¢des have a venerable history; even so, two new examples werereported last year. d-P4S6 5 and e-P4S6 6 were identi¢ed by 31P NMR spectroscopyin the product of the reaction of a-P4S4 with Ph3SbS in CS2.

24 The diagrams illustratethe subtle differences in their structures. Controlled oxidation of [P2S6]

4ÿ in water byhydrogen peroxide leads to [P2S5O]4ÿ and [P2S4O2]

4ÿ via partial substitution ofsulfur with oxygen.25 The second of these substitutions appears to be symmetric,i.e. the [PS2O^PS2O]4ÿ ion forms, while the P^P bond breaks upon further oxygeninclusion (to give [PSO3]

3ÿ and ¢nally H3PO4). Moving on to selenium systems,two examples of the use of CuI as a matrix for PSe systems have been noted. Thuswhen CuI, red phosphorus and selenium are heated in a silica ampoule at 400 �Cfor a number of days orange needles of (CuI)3P4Se4 form; these contain b-P4Se47 cages isolated within the copper halide matrix (such cages have not been seenin the free state, a fact which illustrates the ability of the CuI matrix to stabilisenew species).26 Changing the reaction conditions somewhat allows the isolationof (CuI)P4Se4 in which P4Se3 cages are bridged into in¢nite strands by seleniumatoms.27 Con¢nement of P4Se3 cages within Ni(II) or Cu(II) macrocyclic complexeshas also been demonstrated.28

The high temperature reactions of PSe £uxes continue to provide ef¢cient routes tonew systems. Thus the reaction of P2Se5 £ux with elemental bismuth at 500 �C forthree days yielded black crystals of Bi4(P2Se6)3 (which consists of a 3-D structure

124 Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online

built of ethane-like [P2Se6]4ÿ anions).29 Finally, a study of the reaction of But2PISe

with iodine has revealed that the black product contains both Se^I2 donor andI^P acceptor linkages.30

Moving on to heavier Group 15 elements, reaction of RbCl, Ag[BF4] and Li3AsSe3(molar ratio 4:1:3) in methanol at 130 �C yields red needles of RbAg2As3Se6.

31 Thelatter exhibits a unique 3-D structure generated from [As3Se6]

3ÿ rings; an equallynovel Sb^bound Sb^S ligand is found in [Cr4(CO)12(Sb2S)Cp4] the black productof the reaction of Sb2S3 with [Cr(CO)3Cp]2 in re£uxing toluene.32

A new study of Group 1 and 2 polysul¢des has analysed their Raman spectra inrelation to their X-ray structures and shown that the geometries of both [S2]

2ÿ

and [S3]2ÿ can be corellated with the electric ¢eld of the cation present.33 A similar

study has revealed that irrespective of the precise composition of mixtures of sodiumsul¢des and sulfur, the ¢rst step in their reaction involves the formation of a-Na2S4;at 200 �C the latter reacts with with excess Na2S to give b-Na2S2.

34 Elementalselenium has been shown to react with BuLi in THF to give BuSeSeLi (which provesto be surprisingly stable stored under argon)35 while [PhTe]3

ÿ, the anionic telluriumanalogue to [I3]

ÿ, has been isolated for the ¢rst time.36 The latter anion containsthe Te3 chain in a slightly bent geometry (angle at central Te 173�). Two interestingmixed chalcogen species may be isolated by treating the initial product of thereaction of [Et4N]Cl, Na2S4 and tellurium with sulfur, [Te(S5)(S7)]

2ÿ 8 and theco-crystallised ions [Te(S5)2]

2ÿ 9 and [Te(S7)2]2ÿ 10,37 while HIS2O8 may be obtained

from iodic acid and oleum at 210 �C.38

A very signi¢cant advance in the halide chemistry of chalcogens comes with theisolation of SeCl2, generated in the reaction of selenium with SO2Cl2.

39 The materialitself is an unstable red oil; when dissolved in THF, however, it proves to be stable for24 h at ambient temperatures. It clearly has great promise as a synthon. Two new

Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134 125

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online

binary Se^Cl anions have been characterised for the ¢rst time: [Se2Cl4]2ÿ and

[SeCl6]2ÿ.40 The latter is found in the product of the reaction of dmsu with sulfuryl

chloride and shows essentially octahedral symmetry; storage in solution yields aproduct containing the former, in which two SeCl3 units are linked by an Se^Sebond. In a similar vein, the [SeBr2]

ÿ moiety is found in zwitterionic, T-shapedN,N-dimethyl-2-selenourea^dibromine (the orange product of the bromination ofthe selenourea)41 while solid But3PSeI3 has been shown to consist of cation pairsof the form [(But3PSe)2I]

�2 intercalated between [I5]

ÿ layers.42 The ¢rst exampleof a tri£uorosul¢te salt, [Me4N][SOF3] forms during sonication of a [Me4N]F/SOF2

mixture,43 while thionyl chloride acts as an O-bound ligand in [TiCl4(SOCl2)]2.44

As usual many examples of chalcogenide metal complexes were reported during1999; space will only permit us to consider a small selection, which we do in ascend-ing order of nuclearity. Three isomeric forms of [MSe2HCp2] (M � Nb or Ta) havebeen isolated with the variation stemming from the nature of the Se2H unit.45 Thismay be of the form Z2-Se2H, (SeH)Se or (Z2-Se2)H; the dependence of such formsupon the nature of the metal and their abilities to interconvert have been studiedin detail by X-ray crystallography and NMR (1H and 77Se). Pentagonal pyramidal[NbS(S2)2(SPh)]

2ÿ forms upon treatment of [NbO(S2)2(SPh)]2ÿ with hydride46 while

the high temperature reaction of CrCl3, sulfur and [PPh4]Br in aqueous en leads to agreen salt of [Cr(en)(S5)2]

ÿ (in which the CrS5 unit adopts a chair conformation).47 Inthe presence of H2S the reactive addition of CS2 to [MoS4]

2ÿ leads to[Mo(Z2-CS3)4]

3ÿ (but [Mo2(Z2-CS3)4(S2)2]

2ÿ in its absence)48 while a range ofalkenes have been shown to (reversibly) form adducts with [ReS4]

ÿ.49 Sequentialoxidation and deprotonation allows the formation of [MoO(PMe3)2Cp]

� viahydrolysis of [MoH(PMe3)3Cp]

�,50 while [Co(SH)(cyclam)]� has been shown tobe able to hydrogenate the N�N bond of azobenzene (giving diphenylhydrazine).51

Binuclear systems reported last year include [Nb2(S2)2X8]4ÿ where X � Cl or Br

and which form by acid hydrolysis of [Nb2S4(NCS)8]4ÿ,52 [(NdCp*2)2(m-Z

2:Z2-Se2)(the dark-burgundy product of the one-electron reduction of PPh3Se by [NdCp*3])

53

and the [(TaSCl4)2(diox)]2ÿ anion.54 Black crystalline [Re2Br4(Te2)(TeBr)2(TeBr2)2]

has been reported to form in the high temperature reaction of ReBr4 with telluriumand TeBr4 in SiBr4.

55 Finally, a 53 reference review of the chemistry of[M2(P^P)(m-S)2] systems (M � Pt or Pd, P^P is a diphosphine) is very welcome.56

Among trinuclear systems, red Re3Se7Cl7 forms from ReCl4, selenium and SeCl4at high temperatures and contains the [Re3(m3-Se)(m2-Se2)3Cl6]

� cation57 (as an aside,a 106 reference review of rhenium sul¢de clusters is worthy of note).58 Salts of[Fe3(CO)8(SO2)(S)]

2ÿ and [Fe3(CO)9(SO2)]2ÿ form in the reaction of SO2 with

[MFe3(CO)14] (M � Cr, Mo or W),59 while a series of positional isomers of[Pd3Cl2(Z

2-dppf)(m-dppf)(S)2] have been noted.60

The usual crop of cuboidal complexes have resulted from recent work; examplesinclude [W4(m3-E)4(CN)12]

6ÿ (wherein E � S, Se or Te and which form from cyanideaddition to polymeric halide complexes),61 mixed metal clusters such as[(TiCp)2(RuCp*)2(m3-S)4],

62 and the iron sul¢do species [Fe4S4X4]2ÿ (X � PhS

or Cl).63 The kinetics of the reaction of the latter with [Et2NCS2]ÿ have been

investigated; the same ligand appears in [{M0(cod)}2{MCl(Et2NCS2)}2(m3-S)4](M0 � Rh, Ir; M � Mo, W).64 The ¢rst Te^Mn^Co clusters have been reportedto form in the high temperature reaction of K2TeO3 with [Mn2(CO)10] in methanol.65

126 Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online

Treatment of the initial product, [Mn4(m4-Te)2(CO)12]2ÿ with MeSO3CF3 results in

[(TeMe2)(Mn(CO)4)(m5-Te)(m4-Te)Mn4(CO)12]ÿ, which contains a novel m5-Te

2ÿ

bonding mode. Finally, both bridging S and SO2 are present in tetranuclear[Pd4(SO2)2(S)(CO)(PCH2Ph3)4] which forms from an interesting route involvingthe splitting of the CO and S units in COS.66

The [Re6Se8]2� core has been used to support dendrimer systems67 while the

luminescence spectra of [Re6S8Cl6]3ÿ and [Re6S8Cl6]

4ÿ have been studied;68 otherhexanuclear systems include [Ru6(m3-Se)4(CO)12(m-dppm)2] (which exhibits a64-electron butter£y core)69 and Ag6[Se2P(OPr)i2]6.

70 Among larger cluster unitswe ¢nd [Mo6Fe20S30(Cl4cat)6(PEt3)6] (whose core topologically resembles theP-cluster of nitrogenase),71 [Rb10Mo36S38]

72 and [Cu58Se16(SePh)24(dppa)6] (oneof a series of new CuSe clusters formed in the reaction of CuCl with PhSeSiMe3and bidentate phosphines).73 Finally it has been reported that nanoscale molyb-denum sul¢des may be prepared by the gas-phase decomposition of Mo(CO)6/H2Smixtures in an inert gas reactor at 500^600 �C.74

3 Oxygen

Catalytic oxidation of simple organic systems remains an extremely important areaof work and results from last year re£ect this. Thus sulfated zirconia doped withlithium catalysts was shown to be effective for the oxidative dehydrogenation ofethane to ethylene.75 Not only was a high ethane conversion noted but a highselectivity towards ethylene was also shown. Molecular oxygen may be used asoxidant for the dihydroxylation of simple alkenes when K2[OsO2(OH)4] is presentas a catalyst.76 At pH 10.4 the reaction provides very ef¢cient conversion to diols,with both diol oxygens arising from the O2. [MoO(O2)(QO)2] acts as a catalystfor homogeneous liquid phase oxidation of methylbenzenes (thus toluene may beconverted to PhCO2H in 95% yield with a turnover of 1310, via the active species[MoO(O2)2�2QOH])77 while H3PW12O40 and [Bu4N]4[W10O32] heterogenised onsilica act as photocatalysts for the oxidation of cyclohexane.78 A key feature ofthe latter system is that although it is as ef¢cient as TiO2 oxidative mineralisationprocesses that occur on the titania surface are not observed. Activity for the partialoxidation of ethane to ethene and acetic acid has been noted for Mo/V/M/O(M � Al, Fe, Cr or Ti) metal oxides prepared by hydrothermal routes fromheteropolymolybdates and VOSO4 in water.79

Copper zinc oxide catalysts, prepared by co-precipitation, have been shown todisplay high activity for catalytic oxidation of CO to CO2 under ambient conditions;the effects of ageing time and of the atmosphere under which the prepartion wasperformed were also determined in this study.80 NO2 forms as an intermediatein the selective catalytic reduction of NO by C3H6 in the presence of excess SO2

over alumina.81 It does not, however, arise from direct O2 oxidation of NO; organ-onitro species are postulated as possible progenitors. A high thermal stabilityand high sulfur tolerance, has been noted for alumina-supported uranium oxidecatalysts for NO reduction,82 while the ¢rst observation of an increase in catalyticactivity during hydrocarbon reduction of NOx in the presence of water vapour

Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134 127

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online

has been reported.83 The catalyst in this case is platinum/tungstophosphoric acidsupported on MCM^41 molecular sieves. Vanadium oxide catalysts supportedon niobia have been found to be highly active for ammoxidation of3-methylpyridine,84 while the use of a chiral diferric catalyst in the H2O2 oxidationof sul¢des has been investigated.85 Finally, persulfate modi¢ed Al2O3/ZrO2 actsas an ``extraordinarily'' highly active solid superacid catalyst for n-butane isomerism(an important reaction in the petroleum industry). It proves to be more stable andmore active than any zirconia-based catalyst yet reported.86

Moving on to main-group oxygen concerns, it has long been known that an O4

species forms from the interaction of two O2 molecules.87 A new, detailed, molecularbeam study has now been performed looking at collisions between dioxygenmolecules, during which the ``glory'' effect was observed and the ground state energyof the system calculated (concluding that while van der Waals forces provide most ofthe bonding, there is a contribution from spin^spin interactions). A new route toalkali-metal oxometallates has been reported.88 Reaction of metal azides, nitritesand binary oxides in a custom built reaction vessel at 300^350 �C yields a wide var-iety of systems. This method proves to be very much simpler than previous routesthanks, mainly, to the fact that it does not require the (dif¢cult) formation ofthe metal oxide.Although carbon^oxygen systems largely reside in that nebulous (and often

tedious) domain known as organic chemistry, some CO systems from the past yearare worthy of note here. 1:1 complexes of C3O2 with both water and with ammoniahave been prepared and studied on argon matrices.89 Among the conclusions reachedare suggestions that the O (or N) binds to the C�O carbon and that the resultingproducts are stabilised by H-bonding to the carbonyl oxygen. Oxiranylidene,cyclo-H2COC, is a fundamental carbon^oxygen species which has now been detectedafter £ash photolysis of H2COCC6H6.

90 It was characterised by IR spectroscopy in anitrogen matrix at 10K. Trihydroxycarbenium salts of the type [C(OH)3][MF6] (M� As or Sb) may be isolated from the reaction of carbonic acid with HF/MF5

at ÿ60 �C;91 the ¢rst X-ray crystallographic analysis of such cations reveals aC3 symmetry with a C^O distance of 1.23 Ð. The [OCNCO]� ion, isoelectronic withC2O3 has been generated in the reaction of FCONCO with SbF5.

92 X-Ray structuredetermination of the colourless crystals reveals a bent structure with a 131� angleat the central nitrogen (cf. the isoelectronic linear C3O2 and bent [N5]

�). Finally,IR spectroscopy has been used to monitor the formation of SiOCl2 during the oxygencombustion of SiCl4; the optimal conditions for its formation have been determinedand the SiOCl radical ruled out as a signi¢cant intermediate in the process.93

As usual, nitrogen^oxygen systems have proved to be exceptionally fruitful in1999. Hydroxynitrene, HON, has been prepared for the ¢rst time, by the reactionof H atoms with a NO/Ar mixture at 10 K.94 Though it is actually the minor productof this reaction, the major species, HNO, may be converted through to it viaphotolysis at 313 nm. Calculations suggest that the NO bond in HON is long,ca. 1.32 Ð, indicating that it is intermediate between double and single. Reactionof OF2 with azides results in dinitrogen and N2O [via intermediate formation ofO(N3)2]

95 while the predominant product of the reaction of [N2O3]2ÿ with one-

and two-electron oxidants proves to be nitrite.96 Reaction of amines withhyponitrous acid leads to a range of organic salts of hyponitrite (all of which

128 Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online

are planar with average N�N and N^O distances of 1.24 and 1.38Ð, respectively)97

while peroxynitrite has been shown to react with azide by one-electron reduction togive N3 and NO2 radicals.98 The latter combine to give the intermediate N3NO2

which in turn generates N2O. When generated in situ, peroxynitrous acid has beenshown to rapidly oxidise the thiolato sulfur in [Co(en)2(SCH2CH2NH2)]

2� to give[Co(en)2{S(O)CH2CH2NH2}]

2�.99 Finally in this area, instructive Nobel lectureson NO biology are to be recommended.100^102

Moving down Group 15 to phosphorus, the 23Na MAS and multiple quantumNMR spectra of anhydrous Na5P3O10 polymorphs have been reported (therebyassigning the resonances to the individual sites in the X-ray structures)103 whilethe ¢rst X-ray characterisation of the [P(OH)4]

� cation has been performed for[P(OH)4][SbF6].

104 In the case of the latter all P^O bond lengths prove to be equal(1.55Ð) with the cation showing approximate S4 symmetry. Chains of alternatingCoO4 and HPO4 tetrahedra with pendant HPO4 groups are held together by aH-bonding network in [H3N(CH2)3NH3][Co(HPO4)2] (the ¢rst example of aunidimensional organically templated cobalt hydrogen phosphate)105 while reactionof lanthanide trichlorides with Na[H2PO2] in water leads to products in which fourstructural types are seen.106

The signi¢cant H-bonding interactions within aqueous [Na(18-crown-6)]� salts ofoxo donor atoms have been the subject of an extensive investigation, which hasrevealed them to be both inter- and intra-molecular in nature.107 These results couldshed some light on the ionophore-mediated transport of sodium and potassium ionsacross biological membranes. Moving on to oxo^halogen species, the car-bonylchlorine(I) cation [ClCO]� has been isolated in two separate studies: fromthe reaction of SbF5 with either COCl2

108 or with ClFCO.109 The former reactioncan also generate thermally unstable 1:1 carbonyl halide adducts of SbF5 (or itsAs analogue) in which the ligand acts as an O donor.110 A related cation, [Cl2O2]

�,has been isolated for the ¢rst time (as the [Sb2F11]

ÿ salt); it is found in the blackcrystalline product of the reaction of chlorine with [O2][SbF6] in anhydrous HF.111

It exhibits a planar trapezoidal structure 11 with Cl^Cl 1.92Ð, Cl^O 2.43 Ð andO^O 1.19 Ð. Such bond lengths are consistent with a weak Cl^O interaction anda positive charge located primarily on the Cl2 unit. Indeed, it is perhaps best thoughtof as a charge transfer arrangement between [Cl2]

� and O2. A detailed study of thedecomposition of concentrated hypochlorite at high pH has been performed(concluding that, in the absence of catalytic metal ions, formation of the chlorateion is much faster than the production of O2)

112 while the Cs� salt of the new[IOF5]

2ÿ anion has been reported.113 The latter results from the reaction of CsF,I2O5 and IF5 at 162�C for 14 days; vibrational spectroscopy suggests a pentagonalpyramidal structure.

Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134 129

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online

Investigations into the ionisation of an O3/CHCl2F mixture diluted in O2 havedemonstrated the presence of a remarkable metastable product, namely[HClFO2]

�.114 The key to understanding how unusual this is comes from the factthat in order to form this cation there must have been ¢ssion of all the bonds initiallypresent in the chloro£uorcarbon moiety. The authors presented thermochemicaldata to account for this. An equally remarkable scenario is postulated by the inves-tigators looking at the effects of UV irradiation on water/Xe matrices.115 Theysuggest that the product, HXeOH, may actually be naturally occurring i.e. thatit could form by the action of sunlight on xenon trapped in the depths of polar ice.This is pure speculation of course but it does raise tantalising possibilities.As usual, many oxo^metal complexes were reported last year and here we have

space to look at but a few (again in order of ascending nuclearity). Observationsmade upon vanadyl nitrate in the gas phase indicate a Cs symmetry based on a dis-torted pentagonal bipyramid,116 while solid [MoCl4]

ÿ exists as a square pyramid.117

The formation of CrOCl2 complexes of carbonyls and epoxides during the reactionof CrO2Cl2 with ole¢ns at 10 K has been noted118 while oxygenation of[Rh(dppe)(TpiPr)] leads to a Z2-O2 complex which in turn protonates to give ahydroperoxo complex.119 This result may have important implications for our under-standing of the action of the cytochrome P-450 system. Both [ReO4]

ÿ and [WO4]2ÿ

react with B(C6F5)3 giving air-stable, colourless mono and tris adductsrespectively.120 The continued interest in methyltrioxorhenium is re£ected in theappearance of an excellent review of the atom-transfer reactions it can catalyse(in terms of mechanisms and applications)121 and in the observation that it can acti-vate O2 via a peroxo complex that can then catalyse the conversion of phosphinesto their corresponding oxides.122 In the presence of alkyl hydroperoxides, the relatedspecies methyldioxorhenium decomposes to [ReO4]

ÿ; the organic residue of suchreactions (alcohols, ketones and ethers) indicates that radical reactions occur duringthis process.123

In terms of larger metal^oxo systems, an [O2]2ÿ ion sits in the core of an octahedral

N4K2Mg ring within [{(Me3Si)2N}4K2Mg2(O2)]1 (an example of a so-called``inverse crown ether'')124 while species of the type [M{Mo5O13(OMe)4(NO)}2]

nÿ

(M � Ca, Sr, Ce, etc.) form from M cation addition to [Mo5O13(OMe)4(NO)]3ÿ.125

[Mo6O6S14]4ÿ forms in the solvothermal reaction of MoO3 with TiO2 and

tetramethylammonium hydroxide in aqueous ammonia at 130 �C (and shows threeMo2O2S4 units connected by two m3-S atoms)126 while anions of the type[H7X4Mo6S2O25]

5ÿ (X � P or As) result from the self condensation of [Mo2S2O2]2�

in aqueous arsenate or phosphate at pH 4^5.127 When X � P, 31P NMR has shownthere to be dynamic exchange between the peripheral phosphates and uncoordinatedanions. Amongst octanuclear species we ¢nd [Mo8O26]

2ÿ clusters in[{M(phen)2}2(Mo8O26)] (M � Ni or Co).128 [Mo8V8O40(PO4)]

5ÿ proves to bethe ¢rst polyanion with a tetra-capped Keggin structure;129 a number of Re com-plexes of the [a2-W17P2O61]

10ÿ ligand have also been prepared {of general formula[a2-ReOW17P2O61]

nÿ, where n � 5, 6 or 7 for Re(VII), Re(VI) and Re(V)respectively}.130 Finally a number of super-large systems have been reported includ-ing a pure Mo^O based giant wheel anion bearing 154 Mo atoms131 and some

130 Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online

super-massive examples of so-called ``Keplerates''.132 That papers on the latter referto ``Archimedean synthesis'' and to ``magic numbers'' assures us that the future forthis area will be nothing if not classically motivated!

Ligand/reagent abbreviations used in this chapter

Cl4cat tetrachlorocatecholdmsu N,N-dimethyl-2-selenoureadiox 1,4-dioxanedppa bis(diphenylphosphino)etheneQO 8-quinolateTpiPr tris(3,5-isopropylpyrazolyl)boratettsm tris(trimethylsilyl)methyl

References

1 A. Lindemann, J. Kuchinke and B. Krebs, Z. Anorg. Allg. Chem., 1999, 625, 1165.2 A. Fehlker, R. Blachnik and H. Reuter, Z. Anorg. Allg. Chem., 1999, 625, 1225.3 S. Giesa, J. H. Gross, W. E. Hull, S. Lebedkin, A. Geromov, R. Gleiter and W. Kratschmer, Chem.Commun., 1999, 465.

4 S. Kato, O. Niyomura, S. Nakaiida, Y. Kawahara, T. Kanda, R. Yamada and S. Hori, Inorg. Chem.,1999, 38, 519.

5 G.-C. Guo and T. C. W. Mak, Chem. Commun., 1999, 813.6 M. Friesen and H. Schnockel, Z. Anorg. Allg. Chem., 1999, 625, 1097.7 H. Beckes, J. Breidung, H. Burger, R. Koppe, C. Kotting, W. Sander, H. Schnockel and W. Thiel, Eur.J. Inorg. Chem., 1999, 2013.

8 C. Zimmermann and S. Dehnem, Z. Anorg. Allg. Chem., 1999, 625, 1963.9 C. Wang and R. C. Haushalter, Inorg. Chem., 1999, 38, 595.

10 K. Wraage, T. Pape, R. Herbst-Irmer, M. Noltemeyer, H.-G. Schmidt and H.W. Roesky, Eur. J. Inorg.Chem., 1999, 869.

11 R. Boese, M. Graw, A. Haas, C. Kruger, A. Monicke and J. Schlagheck, Z. Anorg. Allg. Chem., 1999,625, 1261.

12 J. K. Brask, T. Chivers and G. P. A. Yap, Inorg. Chem., 1999, 38, 5588.13 J. Reglinski, D. R. Armstrong, K. Sealey and M. D. Spicer, Inorg. Chem., 1999, 38, 733.14 T. Chivers, D. Gates, X. Li, I. Manners and M. Parvez, Inorg. Chem., 1999, 38, 70.15 T. S. Cameron, A. Decken, M. Fang, S. Parsons, J. Passmore and D. J. Wood, Chem. Commun., 1999,

1801.16 G. Antorrena, J. E. Davies, M. Hartley, F. Palacio, J. M. Rawson, J. N. B. Smith and A. Steiner, Chem.

Commun., 1999, 1393.17 J. Wessel, E. Lork and R. Mews, Z. Anorg. Allg. Chem., 1999, 625, 488.18 A. Maaninen, R. S. Laitinen, T. Chivers and T. A. Pakkanen, Inorg. Chem., 1999, 38, 3450.19 T. Chivers, M. Parvez and G. Schatte, Angew. Chem., Int. Ed., 1999, 38, 2217.20 T. Chivers, G. D. Enright, N. Sandblom, G. Schatte and M. Parvez, Inorg. Chem., 1999, 38, 5431.21 T. Chivers, M. Parvez, G. Schatte and G. P. A. Yap, Inorg. Chem., 1999, 38, 1380.22 I. Foch, L. Parkanyi, G. Besenyei, L. I. Simandi and A. Kalman, J. Chem. Soc., Dalton Trans., 1999,

293.23 P. F. Kelly and A. M. Z. Slawin, Chem. Commun., 1999, 1081.24 H. Nowottnick and R. Blachnik, Z. Anorg. Allg. Chem., 1999, 625, 1966.25 E. Prouzet, M. Fukatani, M. Barj and P. Janvier, J. Chem. Soc., Dalton Trans., 1999, 635.26 A. P¢tzner and S. Reiser, Inorg. Chem., 1999, 38, 2451.27 A. P¢tzner, S. Reiser and H. J. Deiseroth, Z. Anorg. Allg. Chem., 1999, 625, 2196.28 P. C. Andrews, J. L. Atwood, L. J. Barbow, P. D. Croucher, P. J. Nichols, N. O. Smith, B. W. Skelton,

A. H. White and C. L. Raston, J. Chem. Soc., Dalton Trans., 1999, 2927.

Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134 131

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online

29 J. A. Aitken, S. Brown, K. Chondroudis, S. Jobic, R. Brec and M. G. Kanatzidis, Inorg. Chem., 1999,38, 4795.

30 J. Jeske, W. W. duMont and P. G. Jones, Chem.Eur. J., 1999, 5, 385.31 M. Wachold and M. G. Kanatzidis, Inorg. Chem., 1999, 38, 4178.32 L. Y. Goh, W. Chen and R. C. S. Wong, Chem. Commun., 1999, 1481.33 O. El Jaroudi, E. Picquenard, A. Demortier, J.-P. Lelieur and J. Corset, Inorg. Chem., 1999, 38, 2394.34 O. El Jaroudi, E. Picquenard, N. Gobeltz, A. Demortier and J. Corset, Inorg. Chem., 1999, 38, 2917.35 A. Krief, T. VanWemmel, M. Redon, W. Dumont and C. Delmotte, Angew. Chem., Int. Ed., 1999, 38,

2245.36 A. C. Hillier, S.-Y. Liu, A. Sella and M. R. J. Elsegood, Angew. Chem., Int. Ed., 1999, 38, 2745.37 U. Muller and W. Bubenheim, Z. Anorg. Allg. Chem., 1999, 625, 1522.38 M. Jansen and R. Muller, Z. Anorg. Allg. Chem., 1999, 625, 1081.39 A. Maaninen, T. Chivers, M. Parvez, J. Pietikainen and R. S. Laitinen, Inorg. Chem., 1999, 38, 4093.40 P. D. Boyle, S. M. Godfrey and R. G. Pritchard, J. Chem. Soc., Dalton Trans., 1999, 4245.41 P. D. Boyle, W. I. Cross, S. M. Godfrey, C. A. McAuliffe, R. G. Pritchard and S. J. Teat, J. Chem. Soc.,

Dalton Trans., 1999, 2845.42 E. Seppala, F. Rulhe, J. Jeske, W. W. duMont and P. G. Jones, Chem. Commun., 1999, 1471.43 A. Kornath, D. Kadzimirsz and R. Ludwig, Inorg. Chem., 1999, 38, 3066.44 F. Calderazzo, M. D'Attoma, F. Marchetti, G. Pampaloni and S. I. Troyanov, J. Chem. Soc., Dalton

Trans., 1999, 2275.45 H. Brunner, M. M. Kubicki, J.-C. Leblanc, W. Meier, C. Moise, A. Sadorge, B. Stubenhofer, J.

Wachter and R. Wanninger, Eur. J. Inorg. Chem., 1999, 843.46 J. W. Park and S. M. Koo, Inorg. Chem., 1999, 38, 4898.47 H. Rijnberk, C. Nather and W. Bensch, Z. Anorg. Allg. Chem., 1999, 625, 1172.48 C. Simonnet-Jegat, E. Cadusseau, R. Dessapt and F. Secheresse, Inorg. Chem., 1999, 38, 2335.49 J. T. Goodman and T. B. Rauchfuss, J. Am. Chem. Soc., 1999, 121, 5017.50 J. C. Fettinger, H.-B. Kraatz, R. Poli and E. A. Quadrelli, J. Chem. Soc., Dalton Trans., 1999, 497.51 R. J. Pleus, H. Waden, W. Saak, D. Haase and S. Pohl, J. Chem. Soc., Dalton Trans., 1999, 2601.52 M. Sokolov, H. Imoto, T. Saito and V. Fedorov, Z. Anorg. Allg. Chem., 1999, 625, 989.53 W. J. Evans, G.W. Nyce, R. D. Clark, R. J. Doedens and J. W. Ziller,Angew. Chem., Int. Ed., 1999, 38,

1801.54 A. Noll and U. Muller, Z. Anorg. Allg. Chem., 1999, 625, 803.55 J. Beck and K. Muller-Buschbaum, Eur. J. Inorg. Chem., 1999, 839.56 S.-W. Fong and T. S. A. Hor, J. Chem. Soc., Dalton Trans., 1999, 639.57 J. Beck and K. Mutter-Buschbaum, Z. Anorg. Allg. Chem., 1999, 625, 1212.58 T. Saito, J. Chem. Soc., Dalton Trans., 1999, 97.59 R. W. Eveland, C. C. Raymond, T. E. Albrecht-Schmitt and D. F. Shriver, Inorg. Chem., 1999, 38,

1282.60 J. S. L. Yeo, G. Li, W.-H. Yip, W. Henderson, T. C. W. Mak and T. S. A. Hor, J. Chem. Soc., Dalton

Trans., 1999, 435.61 V. P. Fedin, I. V. Kalinina, D. G. Samsonenko, Y. V. Mironov, M. N. Sokolov, S. V. Tkachev, A. V.

Vironets, N. V. Podberezkaya, M. R. J. Elsegood, W. Clegg and A. G. Sykes, Inorg. Chem., 1999,38, 1956.

62 T. Amemiya, S. Kuwata and M. Hidai, Chem. Commun., 1999, 711.63 R. A. Henderson, J. Chem. Soc., Dalton Trans., 1999, 119.64 T. Ikada, S. Kuwata, Y. Mizobe and M. Hidai, Inorg. Chem., 1999, 38, 64.65 M. Shieh, H.-S. Chen, H.-Y. Yang and C.-H. Veng, Angew. Chem., Int. Ed., 1999, 38, 1252.66 S. V. Tarlton, N. Choi, M. McPartlin, D. M. P. Mingos and R. Vilar, J. Chem. Soc., Dalton Trans.,

1999, 653.67 R. Whang and Z. Zheng, J. Am. Chem. Soc., 1999, 121, 3549.68 C. Guilbaud, A. Beluzet, B. Domercq, P. Molinie, C. Coulon, K. Boubekew and P. Batail, Chem.

Commun., 1999, 1867.69 D. Cauzzi, C. Graiff, G. Predieri, A. Tiripicchio and C. Vignali, J. Chem. Soc., Dalton Trans., 1999,

237.70 C. W. Lin, I.-J. Shang, J.-C. Whang and T.-C. Keng, Chem. Commun., 1999, 995.71 F. Osterloh, Y. Sanakis, R. J. Staples, E. Munck and R. H. Holm, Angew. Chem., Int. Ed., 1999, 38,

2066.72 S. Picard, M. Potel and P. Gougeon, Angew. Chem., Int. Ed., 1999, 38, 2034.73 M. Bettenhausen, A. Eichhofer, D. Fenske and M. Semmelmann, Z. Anorg. Allg. Chem., 1999, 625,

593.74 M. R. Close, J. L. Peterson and E. L. Kugler, Inorg. Chem., 1999, 38, 1535.75 S. Wang, K. Murata, T. Hayakawa, S. Hamakawa and K. Suzuki, Chem. Commun., 1999, 103.76 C. Dobler, G. Mehltretter and M. Beller, Angew. Chem., Int. Ed., 1999, 38, 3026.

132 Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online

77 R. Bandyopadhyay, S. Biswas, S. Guha, A. K. Mukherjee and R. Bhattacharyya, Chem. Commun.,1999, 1627.

78 A. Molinari, R. Amadelli, L. Andreottii and A. Maldotti, J. Chem. Soc., Dalton Trans., 1999, 1203.79 W. Ueda, N. F. Chen and K. Oshihara, Chem. Commun., 1999, 517.80 S. H. Taylor, G. J. Hutchings and A. A. Mirzaei, Chem. Commun., 1999, 1373.81 F. C. Meunier, J. P. Breen and J. R. H. Ross, Chem. Commun., 1999, 259.82 S. D. Pollington, A. F. Lee, T. L. Overton, P. J. Sears, P. B. Wells, S. E. Hawley, I. D. Hudson, D. F.

Lee and V. Ruddock, Chem. Commun., 1999, 725.83 A. Jentys, W. Schiesser and H. Vinek, Chem. Commun., 1999, 335.84 K. V. R. Chary, G. Kishan and T. Bhaskar, Chem. Commun., 1999, 1399.85 C. Duboc-Toia, S. Menage, R. Y. N. Ho, L. Que Jr, C. Lambeaux and M. Fontecaue, Inorg. Chem.,

1999, 38, 1261.86 Y. D. Xia, W. M. Hua, Y. Tang and Z. Gao, Chem. Commun., 1999, 1899.87 V. Aquilanti, D. Ascenzi, M. Bartolomei, D. Cappelletti, S. Cavalli, M. deCastro Vitores and F. Pirani,

J. Am. Chem. Soc., 1999, 121, 10794.88 D. Trinschek and M. Jansen, Angew. Chem., Int. Ed., 1999, 38, 133.89 I. Couturier-Tamburelli, T. Chiavassa and J.-P. Aycard, J. Am. Chem. Soc., 1999, 121, 3756.90 G. Maier, H. P. Reisenauer and M. Cibulka, Angew. Chem., Int. Ed., 1999, 38, 105.91 R. Minkwitz and S. Schneider, Angew. Chem., Int. Ed., 1999, 38, 714.92 I. Bernhardi, T. Drews and K. Seppelt, Angew. Chem., Int. Ed., 1999, 38, 2232.93 M. Junker, A. Wilkening, M. Binnewies and H. Schnockel, Eur. J. Inorg. Chem., 1999, 1531.94 G. Maier, H. P. Reisenauer and M. DeMarco, Angew. Chem., Int. Ed., 1999, 38, 108.95 M. J. Crawford and T. M. Klapotke, Inorg. Chem., 1999, 38, 3006.96 A. M. Al-Ajlouni and E. S. Gould, Inorg. Chem., 1999, 38, 1592.97 N. Arulsamy, D. Scott-Bohle, J. A. Imonigre and E. S. Sagan, Inorg. Chem., 1999, 38, 2716.98 S. Padmaja, V. Au and S. A. Madison, J. Chem. Soc., Dalton Trans., 1999, 2933.99 S. Vayssie and H. Elias, Inorg. Chem., 1999, 38, 3439.

100 F. Murad, Angew. Chem., Int. Ed., 1999, 38, 1856.101 R. F. Furchgott, Angew. Chem., Int. Ed., 1999, 38, 1870.102 L. J. Ignarro, Angew. Chem., Int. Ed., 1999, 38, 1882.103 C. A. Fyfe, H. M. zuAltenschildesche and J. Skibsted, Inorg. Chem., 1999, 38, 84.104 R. Minkwitz and S. Schneider, Angew. Chem., Int. Ed., 1999, 38, 210.105 A. R. Cowley and A. M. Chippendale, J. Chem. Soc., Dalton Trans., 1999, 2147.106 J. A. Seddon, A. R. W. Jackson, R. A. Kresinski and A. W. G. Platt, J. Chem. Soc., Dalton Trans.,

1999, 2189.107 J. W. Steed and P. C. Junk, J. Chem. Soc., Dalton Trans., 1999, 2141.108 E. Bernhardt, H. Willner and F. Aubke, Angew. Chem., Int. Ed., 1999, 38, 823.109 K. O. Christe, B. Hoge, J. A. Boatz, G. K. S. Prakash, G. A. Olah and J. A. Sheehy, Inorg. Chem., 1999,

38, 3132.110 B. Hoge, J. A. Boatz, J. Hegge and K. O. Christe, Inorg. Chem., 1999, 38, 3143.111 T. Drews, W. Koch and K. Seppelt, J. Am. Chem. Soc., 1999, 121, 4379.112 L. C. Adam and G. Gordon, Inorg. Chem., 1999, 38, 1299.113 K. O. Christe, W. W. Wilson, D. A. Dixon and J. A. Boatz, J. Am. Chem. Soc., 1999, 121, 3382.114 F. Cacace, G. dePetris, F. Pepi, M. Rosi and A. Sgamellotti, Angew. Chem., Int. Ed., 1999, 38, 2408.115 M. Pettersson, L. Khriachtchev, J. Lundell and M. Rasanen, J. Am. Chem. Soc., 1999, 121, 11904.116 B. A. Smart, H. E. Robertson, D. W. H. Rankin, E. G. Hope and C. J. Marsden, J. Chem. Soc., Dalton

Trans., 1999, 473.117 S. Rabe and U. Muller, Z. Anorg. Allg. Chem., 1999, 625, 842.118 C. Limberg and R. Koppe, Inorg. Chem., 1999, 38, 2106.119 Y. Takahashi, M. Hashimoto, S. Hikichi, M. Akita and Y. Moro-oka, Angew. Chem., Int. Ed., 1999,

38, 3074.120 G. Barrado, L. Doerrer, M. L. H. Green and M. A. Leech, J. Chem. Soc., Dalton Trans., 1999, 1061.121 J. H. Espenson, Chem. Commun., 1999, 479.122 M. D. Eager and J. H. Espenson, Inorg. Chem., 1999, 38, 2533.123 K. A. Brittingham and J. H. Espenson, Inorg. Chem., 1999, 38, 744.124 A. R. Kennedy, E. Mulvey, C. L. Raston, B. A. Roberts and R. B. Rowlings, Chem. Commun., 1999,

353.125 R. Villanneau, A. Proust, F. Robert and P. Gouzerth, J. Chem. Soc., Dalton Trans., 1999, 421.126 J. Ellermeier, C. Nather and W. Bensch, Inorg. Chem., 1999, 38, 4601.127 E. Cadot, A. Dolbecq, B. Salignac and F. Secheresse, Chem. Eur. J., 1999, 5, 2396.128 J. Q. Xu, R.-Z. Wang, G.-Y. Yang, Y.-H. Xing, D.-M. Li, W.-M. Bu, L. Ye, Y.-G. Fan, G.-D. Yang, Y.

Xing, Y.-H. Lin and H.-Q. Jia, Chem. Commun., 1999, 983.129 Y. Xu, H. G. Zhu, H. Cai and X.-Z. You, Chem. Commun., 1999, 787.

Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134 133

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online

130 A. Venturelli, M. J. Nilges, A. Smirnov, R. L. Belford and L. C. Francesconi, J. Chem. Soc., DaltonTrans., 1999, 301.

131 A. Muller, S. K. Das, V. P. Fedin, E. Krickmeyer, Ch. Beugholt, H. Bogge, M. Schmidtmann and B.Haupt£eisch, Z. Anorg. Allg. Chem., 1999, 625, 1187.

132 S. Q. N. Shah, H. Bogge, M. Schmidtmann, S. Sarkar, P. Kogerler, B. Haupt£eisch, A. X. Trautweinand V. Schunemann, Angew. Chem., Int. Ed., 1999, 38, 3238.

134 Annu. Rep. Prog. Chem., Sect. A, 2000, 96, 121^134

Publ

ishe

d on

03

Nov

embe

r 20

00. D

ownl

oade

d by

Uni

vers

ity o

f B

irm

ingh

am o

n 30

/10/

2014

13:

15:5

3.

View Article Online