Indian Journal of ChemistryVol. 21A, December 1982, pp. 1103-1106

Macrocyclic Metal Complexes: Part III-Studies on Fluoro-boro-bridged Macrocyclic Complexes of Cobalt(III)

J CHAKRABARTY, KUNJA B NAIK & B SAHOO·Department of Chemistry, Indian Institute of Technology, Kharagpur 721302

Received 3 May 1982; revised and accepted 13 August 1982

A series of Iluoro-borobridged Co(IlI) macrocyclic complexes of the type CoCy B'X,where Cy represents the rnacrocyclicligand, I, 8-diboro-l, 1,8, 8-tetranuoro-2, 7,9, l4-tetraoxa-3. 6, 10, 13-tetraaza-4, 5, II, 12-tetramethylcyc1otetradeca-3, 5, 10,12-tetraene, [bofamcyc1aene(14)) or I, 8-diboro-l, 1,8, 8-tetranuoro-2, 7, 9, 14-tetraoxa-3, 6, 10, 13-tetraaza-4, 5, II, 12-tetraphenylcyc1otetradeca-3, 5. 10, 12-tetraene, [bofaphcyclaene(l4)), X represents halide ions and B' represents a nitrogendonor base such as pyridine, P-picoline or l'-picoline, have been prepared by the reaction of boron trifluoride on oximecomplexes of the type Co(OximeHhB'X. Structurally important IR bands, viz vC~·N. vN·~·O, vB-O and vB-F have beenidentified. Some of the macrocyclic complexes show the general features of the spectra of octahedral cobalt(lII) complexes,while the spectra of others can be interpreted assuming a C4,. or D4h symmetry. Ligand field splitting parameter 10Dq andinterelectronic repulsion parameter B have been calculated for the octahedral complexes. The tetragonal parameter (Dr) valuesfor low symmetry complexes are all positive and are of the order of 600 em - I. Thermal studies manifest greater thermalstability for [Co(bofamcyclaene-14)B'X) compared to [Co(bofaphcyc1aene-14)B'X). Within a particular series, containing thesame axial halogen atom, the stability is found in the order: [Co(bofamcyclaene-14)PyX) < [Co(bofamcyclaene-14) P-PicX]< [Cotbofamcyclaene-I-tl l'-PicX).

Macrocyclic complexes of cobalt(II1) have been thesubject of several studies covering various aspects ofstereochemistry, electrochemistry and electronicstructure' -II. We have earlier reported the isolation,characterization and structural elucidation of a seriesof fluoro-boro-bridged macrocyclic complexes ofnickel(II), cobalt(II) and copper(II)I1.I3. The presentpaper deals with the isolation of a series of fluoro-boro-bridged macrocyclic complexes of cobalt(III) of thetype CoCyB'X, where Cy represents the macrocyclicligands, I, 8-diboro-l, 1, 8, 8-tetrafluoro-2, 7, 9, 14-tetraoxa-3, 6, 10, 13- tetraaza-4, 5, II, 12-tetra-methylcyclotetradeca-3, 5, 10, 12-tetraene, [bofam-cyclaene(14)] (I, R =CH3) and I, 8-diboro-l, I, 8, 8-tetrafluoro-Z, 7, 9, 14-tetraoxa-3, 6, 10, 13-tetraaza-4, 5,II, 12-tetraphenylcyclotetradeca-3, 5, 10, 12-tetraene,[bofaphcyclaene(14)] (l,R = C6Hs), while X representshalide ions and B' represents a nitrogen donor basesuch as pyridine, p-picoline or v-picoline. Only twosuch complexes with bofamcyclaene (14) such as[Co(bofamcyclaene-14)CH3.H20] and[Cofbofamcyclaene-Jdjf.Hj Py] have been reported I4.

Materials aod MethodsThe parent halo-pyridine-cobalt(III) complexes,

Co(oximeH}zB'X, where oxime H represents mo-noanion of I, 2-dimethylethane-l, 2-dione dioxime(DMG H), B' = pyridine, 3- or 4-methyl-pyridine and X= CI-, Br - or 1-, were prepared following literaturemethods '5. The analogous benzildioximato complexeswere prepared by similar methods.

R = CH3, C6HS

B= PyridiM, 3_methylpyridine,

4 - methyl pyr idine

X =CI-, Br-, 1-

Chloro-pyridine-bisi I, 2-diphenylethane-l, 2-d ion-edioximato) cobalt(III) [Co(C2sH22N404)PyCI]-Toa hot suspension of I, 2-diphenylethane-l, 2-dionedioxime (2.40 g, 0.01 mol) in ethanol (60 ml), cobaltacetate tetrahydrate (1.25 g, 0.005 mol) was added insmall portions and the solution boiled for a fewminutes. To the deep reddish brown solution anaqueous solution of NaCl(O.60 g, om mol) in water(2-3mol) was added and boiled for 3 min. To this wasslowly added pyridine (0.79 g, om mol) and thesolution further warmed for 2-3 min. The mixture wascooled to room temperature and air passed throughthe solution for about 5 hr, when yellowish brown solidseparated out. This was liltered, successively washedwith water, ethanol and ether and dried.

Chloro-pyridine-l, 8-diboro-l, 1,8, 8-tetraj1uoro-2, 7,9, 14-tetraoxa-3, 6, 10, 13-tetraaza-4, 5, II, 12-

1103

INDIAN J. CHEM., VOL. 21A, DECEMBER 1982

tetrameth ylcyclotetradeca-s, 5, 10, 12-tetra-enecobalt(IlI) [Co(bofamcyclaene-14) PyCI]-Chloro-pyridine-bis 0, 2-dimethylethane-l, 2-dionedioxi-mato) cobalt(III)(l g) was suspended in ether (30 m!);to this boron trifluoride etherate (3 ml) was slowlyadded while stirring. The colour of the compoundchanged from yellowish brown to light pink afterstirring for additional 6 hr, left overnight, filtered,washed with ether and recrystallised from acetonitrile.

Chloro-pyridine-t ; 8-diboro-l, 1,8, 8-tetrajluoro-2, 7,9, 14-tetraoxa-3, 6, 10, 13-t~traaza-4, 5, II, 12-tetraphenylcvctotetradeca-Y, 5, 10, 12-tetra-enecobalt(IIl) [Co(bofaphcyclaene-14)PyCI]-lt wasprepared as the [Co(bofamcyciaene-14) PyCI] startingfrom chloropyridine-bis (I, 2-diphenylethane-I, 2-dionedioximato) coba1t(III), [Co(C2sH22N404) PyCl]and crystallised from acetonitrile as reddish browncrystals.Results and Discussion

The analytical data of the complexes are recorded inTable 1. In the preparation of the fluoro-boro-bridgedmacrocycles of the type, Co(Cy)B'X it is important toadd boron-trifluoride etherate at a slow rate withconstant stirring in order to obtain the product in purecrystalline form and to avoid formation of any gummysubstance the formation of which is sometimesobserved. The formation of the macrocycies involvesstepwise processes(l and 2).

2Co(II)+4 Oxime H2+4B'+4X- +to2~

2[Co(oxime HhB'X] + 2B'HX + H20 ... (t)

Co(oxime HhB'X + 2BF 3 ~

Co(oxime BF 2)2B'X + 2HF ... (2)

Table I-Analytical Data for Bofamcyc1aene (14)- and Bofaphcyc1aene (l4)-cobalt(IJI) Complexes

Attempts were made to prepare similar complexeswith pentane-2, 4-dionedioxime ligand, but theanalytical data did not agree satisfactorily.

Thermal studies- TG and DT A in the temperaturerange ambient to IOOO°Cdo not show any mass loss upto 200°C for the macrocycles [Co(bofamcyclaene-14)B'Xl Beyond 200°C these complexes undergoabrupt decomposition as revealed by intenseexothermic peaks. The products of decomposition thenundergo rapid oxidation to C0304 the formation ofwhich is complete -640°C as revealed by no furthermass loss. The chloro, bromo add iodo pyridinecomplexes decompose in the temperature range 230-240°C, /3-picoline series - 250"C and the y-picolineseries 270-8(Ye. The [Co(bofaphcyclaene-14)B'X]series of complexes show an endothermic peak'" IOO'e. After this, the compounds do not show anymass loss for a short range of temperature. This isfollowed by gradual loss in mass as evident from weakendothermic peaks in DT A curve and finally oxidationof the residue takes place at 320-380"C as indicated byan intense exothermic peak in DTA curve and nofurther mass loss due to formation of C0304.

IR spectra (vmax in em-I)-The IR spectra of themacrocycles closely resemble one another butsignificantly difTer from the spectra of the respectiveparent compounds. The parent complexes show peaks3400(w) and r- 1720-1740 (br) due to hydrogen bondedOH groups and deformation vibrations of N -OHgroups respectively. In the spectra of fluoro-boro-bridged complexes, these bands disappear indicatingthe breakdown of the hydrogen bonded bridges andformation of new bonds with > BF 2 groups. The

SI No Complexes Colour Cobalt( 00) N itrogen( '1~) Halogent X)

I CoL,PyCI Pink 11.31( 11.79) 13.80( 14.02) 6.92 (7.10)2 CoL,PyBr Light yellow 1034(10.83) 12.30( 12.87) 14.23(14.71)3 CoL,Pyl Reddish violet 9.38 (9.97) 11.50( 11.85) 19.20(21.49)4 CoL,P-PicCi Light pink 11.18(11.47) 13.46( 13.63) 6.72 (6.91)5 CoL,P-PicBr Light greenish yellow 10.14(10.56) 12.20( 12.54) 14.12(14.34)6 CoL,!J-Picl Dark red 9.25 (9.74) 11.34( 11.57) 19.12(21.00)7 Co L, y-PicCi Light pink 11.20(11.47) 13.58( 13.63) 6.48 (6.91)8 COli y-PicBr Light greenish yellow 10.34(10.56) 12.38(12.54) 14.00( 14.34)9 CoLly-Piel Reddish violet 9.21 (9.74) 11.22(11.57) 18.65(21.00)

10 CoL2PyCI Reddish brown 7.46 (7.88) 9.03 (9.37) 4.34 (4.75)II CoL2PyBr Yellowish brown 7.08 (7.44) 8.56 (884) 9.98(10.10)12 CoL2PyI Chocolate brown 6.78 (7.02) 7.98 (8.34) 14.28(15.14)13 CoL2P-PicCI Orange yellow 7.43 (7.74) 8.98 (9.19) 4.46 (4.66)14 CoL21i-PicBr Yellowish brown 6.96 (7.31) 8.25 (8.69) 9.78 (9.93)15 CoL2tJ-Picl Reddish brown 6.58 (6.91) 8.04 (8.21) 14.00(14.89)16 Co L 2y-PicCI Light orange yellow 7.56 (7.74) 8.92 (9.19) 4.26 (4.66)17 CoL2y-PicBr Greenish yellow 6.85 (7.31) 8.33 (8.69) 9.45 (9.93)18 CoL2y-Piel Reddish brown 6.74 (6.91) 7.88 (8.21) 13.68( 14.89)

L, = bofamcyclaene (14) (CsH '2N.O.B2F .); L2 = bofaphcydaene(14). (C 2sH20N.O.B2F .).Calculated values are given under parentheses .--.---.~--~ .~---- .--.------------~-.--

1104

CHAKRABARTY et al.: MACROCYCLIC CO(llI) COMPLEXES

parent complexes also exhibit strong and intense bandsin the region 1550-1560 IvC~N of coordinated ligand)and a weak satellite at 1605-1615 (vC =C/ 01 vC~N ofpyridine ring), In the macrocyclic complexes, ingeneral, the former band disappears and a new strongand intense band is observed at a higher frequencyregion -1600-1615, From the sharpness and intensityof the band, it is concluded that this band possesses thecharacteristic features of vC:.:'N 16

Two sharp and intense bands - 1230 and 1090respectively in both the parent and macrocycliccomplexes are assigned to vN::~'O, Notable changes areobserved in the region 1200-800 in the spectra of themacrocycles compared to the parent complexes, Themost intense band -1010 has been assigned to vB-Fand the less intense band - 1190 and 830 to vB-O (seerefs 16 and 1T), Besides the deformation mode.vibration of > BF 1 group is observed near 755 eitheras a doublet or a sharp band of medium to strong inintensity 1 8. The above spectral data show that themacrocycles possess the structures shown in I with theligand forming a planar complex unit with the metalion, coordination occurring through the nitrogenatoms. The nitrogen donor base and a halide ioncoordinate with the metal ion from axial positionsorthogonal to the square plane.

Electronic spectra and magnetic properties-All thepresently prepared macrocyclic complexes arediamagnetic, Their electronic spectra, however, are notalways well resolved. But from a consideration of theimportant features of the spectra, it becomes evidentthat, the complexes 2, 4, 5, 7,8, 11, 12, 14and 17 (Table1)possess the general features of octahedral cobalt (I II)complexesI9

.1o

, while the rest i.e. 1,3,6,9,10,13,15,16and 18 show low symmetry ligand field componentsand can be reasonably interpreted assuming anapproximately D4h (or C41,) symmetry.

The series of complexes which possess characteristicoctahedral features in their spectra show three bandsapart from the low-frequency band in the region12,000-13,000 em - I. The bands at 18,000 em - 1 isattributed to the spin allowed transition IAlg~ITlg

while that at 25,000-27,000 em -I is assigned to 1A Ig

~ 1 T 19 transition. The band located in the region29,000 to 31,000 cm-I is highest in intensity andpossibly arises due to M ~ Lzr" charge transfertransitions. The ligand field parameters 10 Dq and Bhave been estimated (Table 2) for these complexeswhich are comparable to [Co(enh]3 + and[Co(enh(NCS)Cl] + complexes+' (Dq values are 2530and 2050 em - 1 respectively).

The spectra of the complexes 1,3,6,9, 10, 13, 15, 16and 18 can be interpreted approximately in terms ofD4h symmetry. They exhibit two bands at 15,000 and

Table 2-Electronic Spectral Data and Ligand FieldParameters for Bofamcyclaene (14)- and Bofa-

phcyclaene (14) Cobalt(III) Complexes

Complex Dq'Y Dr DqZ 10Dq B(em-') (em-') (em-') (cm-')

Col,PyCI 2500 665 1336 (21,200)CoL,f3-PicCI 23.000 534Co L, ;'- PieCI 23,300 468cet., PyBr 22,300 579CoL,f3-PieBr 21,500 538CoL, }'-PicBr 21.660 446CoL,Pyl 2463 746 1160 (20,300)CoL,f3-Piel 2440 675 1257 (20.500)CoL,;'-Piel 2550 720 1290 (21.200)CoL2PyCi 2440 596 lJ97 (20.900)CoL2PyBr 21.700 444CoL2Pyl 21.700 357CoL2f3-PicCI 2380 528 1456 (20.700)CoL2{i-PicBr 21.700 444CoL2f3-Picl 2463 666 1294 (20.800)CoL2;'-PieCI 2360 526 1436 (20.600)CoL2}'-PieBr 21,500 456CoL2y-Piel 2440 640 1320 (20,700)

L, = bofamcyclaene (14), L2 = bofapheyclaene (14),10Dq values under parentheses have been calculated,

21,000 ern - I, attributed, respectively to the transitionsIAIg~IEg and IAIg~IA1g, the split components of1 T1g term under D4h symmetry. Another bandobserved 27,000 or 25,000 cm - 1 is not split and isattributed to the transitions 1A Ig ~ 1T2g state. Thetetragonal ligand field parameter Dt, the in-planeligand field parameter Dqxy and the axial ligand fieldparameter DqZ for the hypothetical octahedral ML6complexes, have been estimated 10 taking the value3800 em - 1 for C, the interelectronic repulsionparameter. Apart from these, the parameters Dq and Bhave been also estimated under an octahedral fieldapproximation, and the data are recorded in Table 2. Itis striking to note that the value of Dqxy derived for thisseries of complexes for which 1T1g term is split isapproximately constant within the limits ofuncertainties in locating the centre of gravity of theband positions.

Dt values estimated for the low symmetry complexesare positive as expected from the planarity of themacrocyclic ligand and the in-plane ligand field isstronger than the axial field. Dqxy values of fluoro-boro-bridged macrocyclic complexes of the type,[Co(bofaphcyclaene-14)B'X] are found to be lowerthan those of [Co(bofamcyclaene-14)B'X] series. Theweak ligand field strength of the former series arisesdue to electron withdrawing nature of the phenyl rings.However, Dqxy values of the complexes ofbofamcyclaene (14) series are comparable to cyclamand DMC (Dqxy = 2480 em -I and 2500 cm-I

1105

INDIAN J. CHEM .. VOL. 21A. DECEMBER 1982

respectively) with saturated N4 donor system 22 but arelower when compared to the ligand field strength ofTIM and I,7-CT system+'. This is reasonable becauseof C, N, Band 0 atoms; oxygen atoms being moreelectronegative and in juxtaposition to N terms, reducethe donor strength of nitrogen atoms and consequentlyweaken the ligand field strength. The role ofelectronegative fluorine atoms at the bridgehead boronatoms further enhances this effect. The axial ligand fieldparameter, DqZ, represents the average of DqZ of thesubstituents, a halide ion and a pyridine base. For thepresent series of complexes, DqZ lie in the range 1100 to1460 cm - 1 and are found to decrease from chloride toiodide for the same axial base, while with the samehalide ion, the DqZ values are in the order Py < p-pic ~y-pic, The parameter DqZ for chloro, bromo and iodocomplexes of the type, [Co LX 2] + (X = Cl - , Br - or 1- )and [CoLIX] + (X = CI- or Br - and L represents cyclicligand) lie in the range 1400-1000 em -I and in theorder I < Br < CI and I < IX. The ligand fieldparameters estimated for the present series ofcomplexes lie within the expected range.

Another interesting feature of the spectra is theappearance of a weak band 11.800 em - 1 for all iodocomplexes. A similar type of band at 13,400 ern - 1 isalso observed for the bromo complexes of the type[Co(bofaphcyclaene-14) B'X] (B' = Py or P-picoline).but is not dominantly observed in other complexes ..This band seems to originate from the spin-forbiddentransition 1 A Ig-+3T1g or its split components+H".

AcknowledgementThe authors are grateful to the UGc, New Delhi for

the award of a teacher fellowship to J C and to the CSIR.

1106

New Delhi for the award of a junior research fellowshipto KBN.

References

1 Lindoy L F, Chem Soc Rei', 4 (1975) 421-441.

2 Martin L v, Dehayes L J. Zomba L J & Busch D H,) Am chemSoc. 96 (1964) 4046.

3 Martin L Y, Hung Y. Jackels S C. Tait A M & Busch D H.) Amchem Soc. 99 (1977) 4029.

4 Curtis N F.) ch<'m Soc. Dolton Trans. (1975) 1212.

5 Vasilevskis J & Olson D C.lllor~ Ci,<'m. 10 (1971) 1228,

6 Hay R W. Bembi R. Hideg K & Hankovszky O.llIargchim Acta.64 (1982) Lln

7 Murakami Y. Aoyama Y & Tada T.lnorg chim AClCl.54 (198 I) LIII.

8 Hay R W, Norman P R, House D A & Poon C.lnorg chi/ll Acta.48 ( 1981) 81.

9 Nonoyama M & Hirai O./IIorltchim Acta. 54 (1981) L 283.10 Searle G H & Dwyer M.I/I{,rg chim Acta. 52 (1981) 251.

II Nishimoto K & Kai E./llorg ('/,i/ll Acta. 58 (1981) 107.

12 Chakrabarty J & Sahoo B.lll<iiall) Chem, 2tA (1982)48.

U Chakrabarty J. Naik Kunja B & Sahoo B,lnt/iall) Ch<'m. 2tA(1982) 370.

14 Schrauzer G N & Windgassen R J.) Am chem Soc. 88( 1966) 3738,

15 Schrauzer G N. lnorg 5.1'11, II (1968) 62.

16 Schrauzer G N. Chem Bel'. 95 (1962) 1438.

17 Jackels S C & Rose N J./llorg Ciwm, t2 (1973)1232.

18 Spitsyn V I. Kolli I D, Balabanova E A & Mironinko 0 N.RussJinorg Chern. 20 (1975) 29.

19 Lever A B P.I norgunic electronic spectroscop y (Elsevier, London)1968, 304.

20 Wentworth R A D & Piper T S. l norg Chem. 4 (1965) 709.21 Lever A B P.I IIorgallic el.,('(rollic spectroscopy (Elsevier. London)

1968, 305.

22 Jackels S C. Farmery K. Barefield E K, Rose N J & Busch D H.Inorg Chem. II (1972) 2893.

23 Ballhausen C J,llllro<illctiollIII ligandjield theory (McGraw-HillBook Company, New York) 1962,260.

24 Jorgensen C K. Absorption spectra and chemical bonding incomplexes (Pergamon Press, London) 1962, 140.