Complexes of substituted benzothiazoles 4. Niskel(I1) complexes of the bidentate benzothiazoles 1,2-bis(2-benzothiazo1y1)benzene and 1,2-bis(2-benzothiazo1yl)ethane

LAURENCE KENNETH THOMPSON,' JOHN CHARLES THOMAS RENDELL, AND GEORGE CHARLES WELLON

Department ofchemistry, Meinoricd Uni~ersity of Newfoundland, S t . John's, NJd., Canada A1B 3x7

Received May 29, 1981

LAURENCE KENNETH THOMPSON, JOHN CHARLES THOMAS RENDELL, and GEORGE CHARLES WELLON. Can. J. Chem. 68,514 (1982).

The nickel coordination chemi5try of two potentially bidentate his-benzothiazole ligands is compared. 1.2-Bis(2-benzothiazoly1)- benzene (OBT), which has an o-phenylene bridge, forms square planar derivatives with Nix, (X = I, CIO,, BF,), octahedral derivatives with Nix, (X = NCS, NO,), and five-coordinate derivatives with Nix2 (X = CI, Br). 1,2-Bis(2-benzothiazoly1)ethane (BBTE), which has an ethylene bridge, forms tetrahedral derivatives with Nix, (X = C1, Br, I) and an octahedral complex with Ni(N03),. Although both ligands are capable of tetrahedral coordination about a cobalt centre, the apparent preference of tetra- hedral coordination with nickel complexes of BBTE seems unusual. The only difference between the two ligands lies in the bridging group between the benzothiazole rings. Stiuctural assignments are supported by ligand field and infrared spectra, magnetic data, and an X-ray structure of the complex [Ni(BBTE)Br,], which has been shown to have a distorted tetrahedral stereochemistry.

LAURENCE KENNETH THOMPSON, JOHN CHARLES THOMAS RENDELL et GEORGE CHARLES WELLON. Can. J. Chem. 60,514 (1982).

On compare la chimie de coordination du nickel de deux ligands bis-benzothiazoles, potentiellement bidentates. Le bis(benzo-2 thiazoly1)-1,2 benzene (OBT), qui a un pont o-phenylene, forme des derives plan carres avec Nix, (X = I, CIO,, BF,), des derives octaedriques avec Nix, (X = NCS, NO,) et des derives pentacoordonnes avec Nix, (X = C1, Br). Le bis(benzo-2 thiazoly1)-1,2 ethane (BBTE), qui a un pont ethylene, forme des derives tetraedriques avec Nix, (C = C1, Br, I) et un complexe octaedrique avec Ni(NO,),. En depit du fait que les deux ligands peuvent avoir une coordination tetraetrique autour du centre cobalt, la preference apparente pour une coordination tetraedrique avec les complexes de nickel du BBTE semble inhabituelle. La seule difference entre les deux ligands reside dans le groupe qui fait le pont entre les cycles benzothiazoles. Les determinations de structure s'appuient sur le champ de ligand et ies spectres infrarouges, les donnees magnetiques et la structure, determinee par diffraction de rayons X, du complexe [Ni(BBTE)Br,] qui ont revele la stereochimie tetraedrique deformee de ce complexe.

[Traduit par le journal]

Introduction Histidine imidazole figures prominently at the

active sites of numerous metalloprotein and metal- 7H2 loenzyme systems. The type 1 copper centres in such enzymes as plastocyanin (1) and azurin (2) contain imidazole groups, as well as sulphur donor groups. We have investigated a number of poly- OBT BBTE functional pseudoimidazole ligand systems in which

FIG. 1. S t ~ c t u r e of 1,2-bis(2-benzothiazolyl)benzene, OBT the donor groups have included benzimidazoles. and l,2~bis(2-benzothiazolylethane, BBTE, benzothiazoles, and imidazolines, all of which are

nitrogen donors similar to histidine (3-7). The bisbenzothiazole ligand 1,2-bis(2-benzothiazoly1)- benzene (OBT; Fig. 1) behaves as an N, donor towards cobalt(II), copper(II), and zinc(I1) salts, with the formation of four-coordinate pseudo- tetrahedral and square planar and six-coordinate derivatives (4). An X-ray structural determination revealed that an almost square planar CuN2CI, chromophore exists in the case of the complex [Cu(OBT)CI,] (8). Little tendency towards tetra- hedral coordination with copper was observed for this system. The bis-imidazoline ligands 1,2-bis(2'- imidazolin-2'-yl) benzene (LP) and 1,2-bis(2'-

imidazslin-2'-y1)ethane (LE) form square planar bis-ligand complexes with nickel salts while cobalt complexes are for the most part tetrahedral (3).

In this study we have investigated the nickel coordination chemistry of the two closely related bis-benzothiazole ligands, OBT and BBTE (Fig. 1; BBTE = 1,2-bis(2-benzothiazoly1)ethane). These ligands are similar to LP and LE except that the imidazoline groups are replaced by benzothiazoles. Reaction of OBT with nickel(I1) salts produced several square planar and octahedral derivatives, but in addition, in the case of the chloro- and bromo-complexes spectral and other data suggest

'TO whom all correspondence should be addressed. the formation of square pyramidal dimersr In

0008-4042/82/0405 14-07$0 1.00/0 01982 National Research Council of Canada/Conseil national de recherches du Canada

Can

. J. C

hem

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

HA

RV

AR

D U

NIV

ER

SIT

Y o

n 06

/30/

14Fo

r pe

rson

al u

se o

nly.

contrast, BBTE produces four-coordinate 1 : 1 ha- lide derivatives which appear to be tetrahedral, a structural difference which must in Dart be a function of the bridging entity between the ben- zothiazole rings. A six-coordinate nitrate deriva- tive is also formed, which appears to be analogous to the OBT derivative and shows that although in general BBTE seems to prefer a tetrahedral bite it can be accommodated at a nickel centre with an N-Ni-N angle of around 90".

Experimental Electronic spectra were recorded on a Cary 17 spectrometer

and infrared spectra were obtained with a Perkin-Elmer model 283 spectrometer. Magnetic susceptibilities were obtained at room temperature by the Faraday method with a Cahn model #7600 Faraday Magnetic Susceptibility system, coupled to a Cahn gram electrobalance. Microanalyses were carried out by Canadian Microanalytical Service, Vancouver. Metal analyses were determined by Atomic Absorption with a Varian techtron AA-5 after digestion of the samples in concentrated HNO, or aqua-regia.

Nickel cotnplexes of OBT and BBTE OBT and BBTE were synthesized according to the procedure

of Rai and Braunwarth (9).

INi,(OBT),C~4l.(CH3J,CO (1) OBT (0.75g; 2.2 mmol) was dissolved in hot acetone (50 mL)

and NiC1,.6H20 (0.52g; 2.2 mmol) dissolved in hot ethanol. The two solutions were mixed and refluxed for 30 min. After 5 min a pale orange solid formed. The product was filtered, washed with acetone, and dried in uacuo at 80°C for 3 h.

[Ni2(OBT),Br4].EtOH (12) OBT (0.75g; 2.2 mmol) was dissolved in ethanol (15 mL) and

triethylorthoformate (TEOF) (10 mL) added. NiBr,.3H20 (2.0 g; 7.3 mmol) was dissolved in ethanol (30 mL), the two solutions mixed and heated on a steam bath. As the volume reduced, an orange semicrystalline solid formed. The product was filtered, washed with TEOF, diethylether, and dried in uacuo at 80°C for 3h .

[Ni(OBT)12] (111) OBT (0.52g; 1.5 mmol) was dissolved in hot acetone (35 mL).

Nil, (0.54g; 1.5 mmol) was dissolved in hot acetone (50 mL) and the solution filtered into the solution of the ligand. The mixture was refluxed until dark green crystals began to form. The product was filtered, washed with acetone, and dried it1 uacuo at 80°C for 3 h.

OBT (0.75g; 2.2 mmol) was dissolved in hot ethanol (15 mL) and added to a solution of Ni(NCS), (0.19 g; 1.1 mmol) in ethanol (50 mL). The mixture was refluxed for 112 h and the volume of the solution reduced to approximately 2 mL. Acetone (10 mL) was added and the green solution allowed to stand overnight. A green crystalline product (IV) was obtained, which was filtered, washed with ethanol/petroleum ether (30/70), and dried in uacuo at 80°C for 3 h. The 1:l thiocyanate complex V was prepared similarly using equimolar quantities of ligand and metal salt.

[Ni(OBTi(N~3),l.&CH,),CO ( VI) OBT (0.52g; 1.5 mmol) was dissolved in ethanol (30 mL).

Ni(N0,),.6H20 (0.44g; 1.5 mmol) was dissolved in ethanol (30

mL), and the two solutions mixed and refluxed for 112 h. The volume of the resulting green solution was reduced to about 2 mL and acetone added until a light green solid formed. The product was filtered, washed with acetone, diethyl ether, and dried in uacuo at 80°C for 3 h.

, - 2, L - - \ ---, OBT (0.52g; 1.5 mmol) was dissolved in hot ethanol (20 mL)

and Ni(C1O4),.6H,O ( 0 . 2 8 ~ 0.75 mmol) was dissolved in hot ethanol (30 m ~ ) . T h e solutions were mixed and refluxed for 112 h. On reducing the volume of the solution a yellow-orange solid began to form. Acetone was added to aid precipitation and the product filtered, washed with acetone, and dried in cacuo at 80°C for 3 h. [Ni(OBT),](BF4),~2H,0~2(CH3)ZC0 was prepared similarly using acetone as solvent.

[Ni(BBTE)X,](X = Cl, Br) (IX, X), [Ni(BBTE)Z,].EtOH(XI), [Ni(BBTE)(NQ,),].%tOH (XII)

BBTE (0.75g; 2.5 mmol) was dissolved in hot ethanol (50 mL), NiC1,.6H,O (1.8g; 7.5 mmol) was dissolved in hot ethanol (50 mL), and the two solutions mixed. TEOF (10 mL) was added and the mixture heated under vacuum until the solution volume was reduced sufficiently to produce purple crystals. The reac- tion mixture was warmed for an additional 2 h and the product filtered, washed with TEOF, petroleum ether and dried in cacuo at 80°C for 3 h. The bromide, iodide, and nitrate complexes were prepared similarly.

Analytical data for all the complexes are given in Table 1. Physical measurements on the nickel complexes of OBT and BBTE were possible only in the solid state because of their general insolubility in common solvents and also their solvolytic instability. Also none of the OBT complexes could be obtained in a crystalline form suitable for X-ray analysis.

Results and discussion The chloride and bromide complexes (I, 11) have

electronic spectra which are not typical of square planar, octahedral, or tetrahedral nickel(I1) deriva- tives. They are paramagnetic compounds with major absorptions around 12000 and 21 000 cm-I (Cl) and 11 000 and 20000 cm-' (Br) (Table 2; Fig. 2). Five-coordinate trigonal bipyramidal nickel(I1) derivatives with nitrogen ligands in general have some absorption below 10 000 cm-' with up to five major absorptions in the spectrum. For the trigonal bipyramidal complex [Ni(Me,tren)(NCS)]NCS. H 2 0 absorptions are observed at 7700, 13200, 16 200, 12 100, 24 600 cm-I. A similar spectrum is observed for [Ni(Me,tren)Br]Br with the band positions shifted to slightly lower energy (10). It seems unlikely therefore that I, I1 have trigonal bipyramidal structures. However, a square pyra- midal stereochemistry at nickel seems quite plausi- ble. Systems of the type [Ni(dtp),am] (dtp = (C2H,0),PSS-; am = secondary amine, pyridine, quinoline) (11, 12) are reported to have square pyramidal structures and exhibit two major absorp- tions around 13 000 and 21 000 cm-l.

The infrared spectra of compounds 1, I1 are similar, except in the low energy region (Table 3).

Can

. J. C

hem

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

HA

RV

AR

D U

NIV

ER

SIT

Y o

n 06

/30/

14Fo

r pe

rson

al u

se o

nly.

516 CAN. J . CHEM. VOL. 60, 1982

TABLF, 1. Analytical and other data

Found (%) Caicd. (96)

Compound Colour C H N M C H N M

I, [Ni,(OBT)ZC14].(CH3),C0 Orange-brown 50.9 2.97 5.49 11.4 51.3 2.98 5.56 11.7 11, [Ni,(OBT),Br,l.EtOH Orange-brown 43.3 2.47 4.58 9.87 43.0 2.56 4.78 10.1

111, [Ni(OBT)I,] Darkgreen 36.6 1.99 4.12 9.20 36.5 1.83 4.26 9.00 IV, [Ni(OBT),(NCS),I Pale green 58.2 2.82 9.62 6.51 58.4 2.78 9.73 6.83 V, [Ni,(OBT)2(NCS),(H20),I.(CH3)ZC0 Pale green 49.6 2.98 9.81 9.83 49.8 3.00 9.89 10.42

VI, [Ni(OBT)(N03)21~HCH3)2C0 Green 46.6 2.96 10.3 11.2 46.4 2.70 10.1 10.6 VII, [Ni(OBT),1(C10,)2~2H,0 Orange 48.5 2.88 5.36 5.83 48.9 2.85 5.70 6.01

VIII, [Ni(OBT),1(BF4)2.2(CH3)zC0.2H20 Orange 51.7 3.47 5.21 5.48 51.4 3.73 5.22 5.49 IX, [Ni(BBTE)C12] Purple 45.1 2.63 6.52 13.1 45.1 2.84 6.58 13.8 X, [Ni(BBTE)Br,] Purple 37.2 2.07 5.39 11.2 37.3 2.38 5.44 11.4

XI, [Ni(BBTE)I,].EtOH Green 33.1 2.55 4.40 8.90 33.0 2.75 4.30 8.96 XII, INi(BBTE)(NO,),I.+EtOH Green 40.5 2.29 11.4 11.3 40.6 2.98 11.2 11.7

TABLE 2. Electronic spectra (mull transmittance) (cm-') (a) Five-coordinate and square planar

Compound Spectra

I, [Ni,(OBT),C141.(CH,)2C0 [8400], [ll500], 12500, 16 100, 21 300 II, [Ni,(OBT),Br,l.EtOH [8 7001, [10900], 11 700,15 300,20 300 [25 0001

111, [Ni(OBT)I,I 10400, 18500, 27 800 (CT) VII, [NI (OBT)~] (CIO~)~ .~H,O -

VIII, [Nl(OBT)21(BF4)2.2(CH3)ZC0.2H20 -

(b) Octahedral

3T2, c 'AZg IEg + 3A2g 'Tlg + 3A2g 3T~g(PI +'A,, Compound v I v2 v3 nq B P

IV, [Ni(OBT),(NCS),] 9 800 16 100 - 980 933 0.90 V, [Ni2(OBT)2(NCs)4(H20),I.(CH3)2C0 9 500 15 400 - 950 826 0.79

VI, [Ni(OBT)(N03)21.HCH3)2C0 9 100 [12700] 15 400 25 800 910 866 0.83 XII, INi(BBTE)(N0,)21.:EtOH 8 800 14000 17 500 23 800 880 765 0.74

( c ) Tetrahedral

3A2 t 3T1 IE + 3T1 3T1 (P) + 3T1 Compound vz v3 CT Dq B P

IX, [Ni(BBTE)Cl,] 9800 [12 1001 17200[18700] 530 947 0.91 X, [Ni(BBTE)Br,] 10 100 [11600] 15 900[18 7001 547 901 0.86

XI, [Ni(BBTE)I,].EtOH [10000]10600 14600[16400] 17900 553 767 0.74

A single band in the chloro-complex, assigned to terminal Ni-Cl stretch, occurs at 300 cm-l, while for the bromo-derivative a similar band occurs at 236 cm-l. Other absorptions at 238, 245 cm-' (Cl) and 219 cm-' (Br) are assigned to bridging nickel halogen stretch. The similarity of the electronic spectra of these complexes with known square pyramidal systems and the presence of infrared bands attributable to both terminal and bridging nickel-halogen bonds suggests a square pyramidal dimeric structure for I and 11 involving halogen bridges. The presence of single absorptions asso- ciated with terminal nickel-halogen stretch also indicates trans- rather than cis-dimeric structures (Fig. 3). The other isomer involving a trans-

arrangement of terminal metal halogen bonds in which a non-equatorial arrangement of ligands would exist is considered unlikely on steric grounds.

The iodide complex (111) exhibits three major bands in its mull transmittance spectrum. The high energy absorption at 27 800 cm-' is clearly charge transfer in origin while the other bands at 18 500 and 10400 cm-' can be associated with a square planar iodo-derivative (13, 14). The diamagnetic nature of this system also supports the square planar struc- ture.

The thiocyanate complexes (IV, V) exhibit typi- cally octahedral mull transmittance spectra (Table 2) although in both bases the v3 transition appears

Can

. J. C

hem

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

HA

RV

AR

D U

NIV

ER

SIT

Y o

n 06

/30/

14Fo

r pe

rson

al u

se o

nly.

THOMPSON ET AL.

FIG. 2. Electronic spectra (mull transmittance) of [Ni,(OB- T),Cl,].(CH,),CO ( A ) and [Ni(BBTE)Cl,] (B) .

FIG. 3. Proposed structure for [Ni,(OBT),X,] (X = Cl, Br).

to be hidden among high energy charge transfer absorptions. Although stereochemicall y com- pounds IV and V appear to be similar, in other respects they differ structurally. The 1:2 complex [Ni(OBT),(NCS),] (IV) exhibits CN stretching bands at 2095 and 2106 cm-I, associated with two cis-isothiocyanate groups. Other bands at 296 and 310 cm-I, assigned to Ni-N stretch, are also consistent with such an arrangement. Consequently a cis-octahedral structure involving a NiN, chro- mophore is indicated for this system. The 1: 1 thio- cyanate complete (V) exhibits a more complex infrared spectrum in the CN stretching region. Three bands are observed at 2100, 21 17, and 2140 cm-I. The 2140 cm-' band is too high in energy to be associated with a terminally bound isothiocya- nate and a thiocyanate bridge is suggested. The two lower energy absorptions appear to be more typical of terminally bound thiocyanate. In light of the stoichiometry ofthe complex and the fact that it has a pseudo-octahedral stereochemistry a di-p-thio- cyanate bridged dimeric structure appears to be

0 . * 0 U - .* .* - i & C) e, e, ?C

~ ~ - G W Q \ P J G c w m m e SSm-.? .? 2 2 ??is.? $ m m ~ m m m

m 2 5 m m m m - . * .* .- B CI n n rn = - 0

-3 5 E "E

Can

. J. C

hem

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

HA

RV

AR

D U

NIV

ER

SIT

Y o

n 06

/30/

14Fo

r pe

rson

al u

se o

nly.

518 CAN. J . CHEM. V(

reasonable with a trans-arrangement of OBT lig- ands and two cis-terminal thiocyanates. The re- maining coordination sites appear to be occupied by water molecules as indicated by infrared absorp- tions at 3340 and 3390 cm-' (Fig. 4). Molecular models indicate that the isomer involving a cis non-equatorial arrangement of OBT ligands is unlikely because of steric crowding.

The nitrate complex [Ni(OBT)(N0,),].HCH3),- GO (VI) exhibits mull transmittance bands typical of pseudo-octahedral nickel(I1) (Table 2). Nitrate fundamental infrared absorptions (Table 3) suggest the presence of bidentate nitrate (15) and this is confirmed by the appearance of just two bands in the combination (v, + v4) region separated by 32 cm-I (16). A cis-octahedral structure is therefore suggested involving one coordinated QBT and two bidentate nitrate groups.

The nickel perchlorate and tetrafluoroborate derivatives of OBT (WI, VIII) are clearly square planar in structure involving two bidentate ligands acting as N, donors. No clearly defined d-d bands are observed below 25000 cm-I in their mull transmittance spectra (Table 2) where one might reasonably expect to see such absorptions due to a square planar NiN, chromophore and it is assumed that they are buried beneath high energy charge transfer bands. The diamagnetism of VII and VIII (Table 3), coupled with infrared data (Table 3) indicating the ionic role of the perchlorate and tetrafluoroborate groups confirms the square planar nature of these systems.

The nickel coordination chemistry of the ethyl- ene bridged bis-benzothiazole BBTE (Fig. 1) dif- fers markedly from that of OBT. It has not been found possible to synthesize square planar deriva- tives of BBTE. In fact with nickel perchlorate and tetrafluoroborate no significant complex formation was observed. Nix, (X = ClO,, BF,) and BBTE were reacted in ethanol1TEOF with warming but on cooling the ligand crystallized out and no complexes were formed. In the cases involving nickel halide complexes forcing conditions were required to effect complex formation. Excess metal salt was employed in each case under anhydrous conditions using TEOF and the mixtures were heated until the product crystallized from the hot

FIG. 4. Proposed structure for [Ni,(OBT),(NCS),(H,- O),I~(CH,),CO.

solution. The products are solvolytically unstable and if the reaction solutions are cooled before the product is allowed to crystallize only the ligand is obtained.

Highly coloured paramagnetic derivatives are obtained with nickel halides, Nix, (X = C1, Br, I) (IX-XI). Two major areas of absorption are ob- served in their mull transmittance spectra (Table 2; Fig. 2) corresponding to the v2 and v3 transitions associated with tetrahedral nickel (11). A high energy absorption at 17 900 cm-' in the case of the iodo-complex is associated with iodine-to-metal charge transfer. In each case two infrared absorp- tions associated with nickel halogen stretch are observed (Table 3) consistent with a pseudo- tetrahedral stereochemistry. The nitrate complex [Ni(BBTE)(NO,),].+EtOPI (XII) exhibits electron- ic spectral bands typical of a pseudo-octahedral nickel(1I) system (Table 2) and nitrate combination bands in the infrared (Table 3) separated by 50 cm-' indicate the presence of two bidentate nitrate groups. Structurally therefore the nitrate deriva- tives of both OBT and BBTE appear to be analo- gous.

Crystal field splittings for the pseudo-tetrahedral halide complexes are very similar, but it is some- what surprising that the Dq values rise slightly in the series C1 < Br < I. The Racah parameter B decreases as expected (C1> Br > I) reflecting more covalent character in the complexes as the size of the halogen increases. The v, transition increases in energy in the series C1 < Br < I while the v3 transition decreases in energy (C1> Br > I). It was not possible to observe the v, transition in any of these complexes. The slight increase in v, may reflect a distortion towards a square planar ster- eochemistry as the size of the halogen increases. In the case of the bromo-complex X-ray data indicate a somewhat flattened tetrahedron. This slight in- crease in v2 appears to be responsible for the slight increase in Dq in the series C1 < Br < I. In the tetrahedral complexes Ni(Ph,PQ),X, (X = C1, Br, I) V, decreases slightly in the series C1 > Br > I paralleling the trend in Dq (17). The complex Ni(BBTE)Br, has a crystal field splitting compara- ble with that of the tetrahedral complex Ni(2,3- dirnethylpyridine),Br, (Dq = 540 cm-I). However, the dimethylpyridine complex has more covalent character (p = 0.75) (18).

A comparison of the two ligands, both of which act as N, donors and form seven-membered chelate rings, reveals a possible reason why square planar NiN, derivatives are not formed in the case of BBTE. The only daerence between the two ligands lies in the bridging unit which is an o-disubstituted

Can

. J. C

hem

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

HA

RV

AR

D U

NIV

ER

SIT

Y o

n 06

/30/

14Fo

r pe

rson

al u

se o

nly.

THOMPSON ET AL. 519

benzene in OBT and an ethylene, -CH2CH2--, in BBTE. Molecular models indicate that two OBT ligands fit, without serious steric problems, in a trans-configuration about a square planar metal centre but that axial coordination would be effec- tively prevented by the proximity of two a benzene ring protons per ligand to the fifth and sixth coordination sites. (A cis-configuration proposed in the case of the complex [Ni(OBT),(NCS),] also seems reasonable.) The formation of a similar bis-ligand derivative involving BBTE seems less likely in either a cis- or a trans-configuration because of potentiai steric interactions betweea ethylene bridge protons and a benzene ring pro- tons. Although molecular models indicate that a square planar mono-ligand system involving BBTE is reasonable, the fact that tetrahedral derivatives predominate may be a consequence of the larger ethylene bridge, which is more flexible than the o-phenylene bridge present in OBT and which can accommodate a larger bite about the metal centre.

An X-ray structural investigation of the complex [Ni(BBTE)Br,] confirms the pseudo-tetrahedral nature of this molecule (Fig. 5) (19).

Crystal data for C,,H,,Br,N,S2Ni fw = 514.5 Space group A2/a, a = 19.401(1), b = 7.7995(4), c = 13.340(1) A, fi = 122.280(4)", V = 1706.6A3, z = 4, D, = 1.9968 ~ m - ~ , p = 9.9 mm-I, molecular

symmetY , 2-fold axis. (CuKa radiation, ha, = 1.54056 )

Selected bond lengths and bond angles are listed in Table 4.

The N-Ni-N angle is very close to the tetra- hedral angle but the Br-Ni-Br angle is signifi- cantly larger than 109F and the tetrahedron itself is somewhat compressed. Bond lengths to the nickel centre and in the ligand itself are considered to be normal and the molecule has a two-fold symmetry axis through the nickel centre and a torsional angle of 99. lo in the ethylene bridge.

TABLE 4. Selected bond lengths and bond angles for C,,H,,Br,N,S,Ni (esd in parentheses)

Length Angle Bond (A) Bonds (deg)

The tetrahedral structure observed for this sys- tem and also for the corresponding chloro- and iodo-complexes seems somewhat unusual on two counts; nickel does not usually have a strong preference for tetrahedral geometries, although in some cases steric factors influence the situation, and also other bidentate pseudo-imidazole ligands have been shown to form only square planar and octahedral complexes with nickel even with a system involving an ethylene bridge. In earlier work we have shown that for the ethylene bridged bis-imidazoline LE (3) square planar bis-ligand complexes are formed with nickel halides, while cobalt derivatives, Co(LE)X2 (X = C1, Br, I, NCS), are tetrahedral. X-ray data confirm that the cobalt derivative Co(LE)P, has a tetrahedral structure in which the seven-membered chelate ring has similar dimensions to that in Ni(BBTE)Br2 and the tor- sional angle in the ethylene bridge is 113.6" (20). BBTE also forms tetrahedral derivatives, Co(BB- TE)X2 (X = C1, Br, I, NCS), with cobalt salts (21).

The formation of 1: 1 tetrahedral derivatives of BBTE with the nickel halides appears, in part, to be a function of the ethylene bridge, which is some- what larger and more flexible than an o-phenylene bridge and so would allow the ligand to span two tetrahedral coordination sites more readily than OBT. Also the size of the benzothiazole groups themselves must be taken into account. They are larger than the imidazoline rings found in LE and could be responsible for a steric effect which is helping to stabilize the tetrahedral structure. There appear to be no other steric phenomena in the structure, e.g., hydrogen bonding contacts, which could contribute to the stability of the tetrahedral arrangement. The crystal field strengths of the two ligands must of necessity be very similar and so it is unlikely that electronic effects are responsible for the enhanced stability of the tetrahedral stereo- chemistry in the cases of the BBTE complexes.

Acknowledgement We thank the Natural Sciences and Engineering

Research Council of Canada for financial support. FIG. 5. X-ray structure for [Ni(BBTE)Br,] (R = 0.027).

Can

. J. C

hem

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

HA

RV

AR

D U

NIV

ER

SIT

Y o

n 06

/30/

14Fo

r pe

rson

al u

se o

nly.

520 CAN. J . CHEM. VOL. 60, 1982

1. D. M. COLMAN, H. C. FREEMAN, J . M. CUSS, M. MURATA, V. A. NORRIS, J . A. M. RAMSHAW, and M. P. VENKATAP- PA. Nature, London, 272, 3 19 (1978).

2. E. T. ADMAN, R. E. STENKAMP, L . C. SIEKER, and L. H. JENSEN. J . Mol. Biol. 123, 35 (1978).

3. A. B. P. LEVER, B. S. RAMASWAMY, S. H. SIMONSEN, and L . K. THOMPSON. Can. J . Chem. 48.3076 (1970).

4. J . C. T. RENDELL and L. K. THOMPSON. Can. J . Chem. 57, l(1979).

5. L . K. THOMPSON, R. G. BALL. and J . TROTTER. Can. J . Chem. 58, 1566 (1980).

6. D. V. BAUTISTA and L . K. THOMPSON. Inorg. Chim. Acta, 42, 203 (1980).

7. A. W. ADDISON, H. M. J. HENDRIKS, J. REEDIJK, and L. K. THOMPSON. Inorg. Chem. 20, 103 (1981).

8. R. G. BALL and J . TROTTER. Can. J . Chem. 57,1368 (1979). 9. C. RAI and J . B. BRAUNWARTH. J . Org. Chem. 26, 3634

(1961). 10. I. BERTINI, M. CIAMPOLINI, P. DAPPORTO, and D. GAT-

TESCHI. Inorg. Chem. 11, 2254 (1972).

11. C. K. JQRGENSEN. Acta Chem. Scand. 17, 533 (1963). 12. R. L. CARLIN. J . S. DUBNOFF, and W. T. HUNTRESS. R O C .

Chem. Soc. 228 (1964). 13. A. B. P. LEVER. J . Inorg. Nucl. Chem. 27, 149 (1965). 14. M. GOODGAME and D. M. L. GOODGAME. J. Chem. Soc.

207 (1963). 15. N. F. CURTIS and Y. M. CURTIS. Inorg. Chem. 4, 804

(1965). 16. A. B. P. LEVER, E. MANTOVANI, and B. S. RAMASWAMY.

Can. J . Chem. 49, 1957 (1971). 17. M. GOODGAME, D. M. L. GOODGAME, and F. A. COTTON.

J. Am. Chem. Soc. 83,4161 (1961). 18. S. BUTTAGNI. L. M. VALLARINO, and J. V. QUAGLIANO.

Inorg. Chem. 3, 480 (1964). 19. A. W. HANSON. Cryst. Stmct. Commun. In press. 20. S. H. SIMONSEN Private communication. 21. L. K. THOMPSON andG. C. WELLON. Unpublished results.

Can

. J. C

hem

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

HA

RV

AR

D U

NIV

ER

SIT

Y o

n 06

/30/

14Fo

r pe

rson

al u

se o

nly.