Synthesis, structure and electrochemical behaviour of octahedral nickel(II) complexes with one 1,1-dithio and one macrocyclic ligand

0277-5387/90 $3.00+.00 0 199tl Pergamon Press plc

PolyhehnVol.9,No. 14,~~. 1729-1735, 1990 Printed in Great Britain

SYNT~IS, STRUC~RE AND ~LE~ROCHEMICAL BEHAVIOUR OF OCTAHEDRAL NICKEL(II) COMPLEXES WITH ONE l,l-DITHIO AND ONE MACROCYCLIC LIGAND R. VICENTE,* Departament

A. ESCUER and J. RIBAS

de Quimica Inorganica, Universitat de Barcelona, Diagonal 647, 08028-Barcelona, Spain and A. DE1

Dipartimento

di Chimica, Universid degli Studi di Firenze, Via Maragliano 75-77, 50 I 44-Firenze, Italy and X. SOLANS

and T. CALVET

Departament de Cristal.lografia i Mineralogia, Universitat de Barcelona, C/Marti Franquts s/n 08028-Barcelona, Spain (Received 8 November 1989 ; accepted 26 March 1990)

Abstract-The synthesis and electrochemical behaviour of [Ni(Dr.KTH)L](CI04) and [Ni(Cy)L’](ClO,), where DL-CTH is the racemic isomer of 5,5,7,12,12,14-hexamethyl1,4,&l 1-tetraazacy~lotetrade~ne, Cy is 1,4,8,11-tetraaza~yclotetrad~ane (Cyclam), L is dimethyldithiocarbamate (Me2Dtc), diethyldithiocarbamate (Et,Dtc), pyrrolidindithiocarbamate (PyrrDtc), ethylxanthogenate (Etxant), thioacetate (Tat) and acetate (AC) and L’ are the same ligands except Tat and AC, are described. The structure of mi(DL-CTH) (Et,Dtc)](ClO,) is also reported. This complex crystallizes in the monoclinic space group P2,/a with cell parameters a = 19.551(4), b = 13.446(3), c = 11.428(3) A, /I = 95.54(3) and Z = 4. The isolated ~i(DL-~TH)(Et~Dtc)]+ cation shows a distorted cis-octahedral coordination around the nickel(I1) ion. The electrochemistry of these compounds indicates oxidation processes but with decomposition of the organic part, giving nickel(I1) species with, probably, polymeric dithio derivatives.

The chemistry of derivatives derived from nickel(I1) and l,l-dithio ligands has been extensively studied. ‘**All these compounds have two 1,l -dithio ligands, giving square-planar geometries with some rare octahedral exceptions. 3*4They have interesting properties from industrial, iv2electrochemical’ and magnetic L*2*6 points of view. On the other hand, the properties of the macrocyclic cations wi(DLCTH)]‘+, [Ni(Cy)]‘+ and their derivatives have

been extensively studied. 7*8These square-planar macrocyclic compounds have the possibility of folding, principally when they react with chelate ligands, to yield octahedral mixed-ligand compounds. Starting from this kind of reaction it would be interesting to synthesize new 1,1-dithio complexes in which the presence of the macrocyclic ligand allows the coordination of only one 1,ldithio derivative. We report here two series of these new octahedral nickel(I1) compounds with l,l*Author to whom correspondence should be addressed. dithio ligands and the above mentioned Cyclam and 1729

1730

R. VICENTE

DL-CTH derivatives, being, consequently, the first rare octahedral complexes with only one 1, I-dithio ligand. Acetate and thioacetate derivatives with [Ni(oL-CTH)]+ have been also prepared, with the aim of comparing the properties of sulphur derivatives with the oxygen ones. Electrochemistry of these new compounds has been studied to analyse the electrochemical behaviour of complexes with this unusual coordination with only one 1,I-dithio ligand and to compare with the most common square-planar bis( 1,l -dithioligand)Ni”. Starting from the electrochemical properties of these ligands, we studied the stabilization of the coupled nickel(H)-organic radical, related to [Ni(DLCTH)L]+, with L being an O-donor ligand, previously reported.’ EXPERIMENTAL Synthesis The complex [Ni(DL-CTH)](ClO,), was prepared by the method described by Tait and Busch.g The complex [Ni(Cy)](ClO& was prepared by the method described by Bosnich et a1.7bAcetate, thio and dithio ligands (alkaline salts, Fluka) were used without purification. CTH derivatives. Equimolar amounts of mi(DLC-WI(ClO,), and the corresponding acetate, thioacetate or 1,1-dithioalkaline salt, dissolved in the minimum amount of water, were mixed. The yellow colour of the solution immediately changed to blue-green, and the adduct compounds precipitated within a few minutes. Cyclam derivatives. The same procedure was used, but some differences were observed. After mixing the reagents, no change in the colour of solution was observed and a violet precipitate was gradually formed in 5-6 h (Me,Dtc and Et,Dtc) or 2 days for PyrrDtc. For L = Etxant, after 1 day, an

Table 1. Analytical Compound

lWCTW@WlW~Qd [Ni(CTH)(Tac)](ClO,) [Ni(CTH)(Me,Dtc)](ClO,) [Ni(CTH)(Et,Dtc)](ClO,) [Ni(CTH)(PyrrDtc)](ClO,) pi(CTH)(Etxant)](ClO,)

[Ni(Cy)(Me,Dtc)l(ClO,) [Ni(Cy)(Et,Dtc)l(ClO,)

[Ni(Cy)(PyrrDtc)l(Clo,) [Ni(Cy)(Etxant)](ClO,)

et al.

unidentified precipitate was removed by filtration. After a further day with constant stirring, a violet precipitate was formed. Recrystallization of this latter compound in acetonitrile gave the new complex as a microcrystalline powder. All the compounds are insoluble in water but very soluble in acetone, methanol and acetonitrile. Yield 20% for [Ni(Cy) (Etxant)](C104) and 80-90% for the remaining compounds. Attempts to prepare acetate and thioacetate derivatives under the same conditions were unsuccessful. Analytical data are summarized in Table 1.

Crystal structure determination A prismatic crystal (0.1 x 0.1 x 0.2 mm) was selected and mounted on a Philips PW-1100 fourcircle diffractometer. Unit cell parameters were determined from automatic centring of 25 reflections (4 < 0 Q 12”) and refined by least-squares methods. Intensities were collected with graphite monochromatized MO-K, radiation, using the oscan technique, with scan width 0.8, scan speed 0.03” s- ‘. 2456 reflections were measured in the range 2 < 8 < 25”; 1700 of which were assumed as observed when applying the condition Z > 2.50(Z). Three reflections were measured every 2 h as orientation and intensity controls, and no significant intensity decay was observed. Lorentz-polarization but no absorption corrections were made. The structure was solved by direct methods, using the MULTAN system of computer programs,” and refined by full-matrix least-squares, using the SHELX76 computer program. ’ ’ The function minimized was C w[[F,] - [FJ12, where w = (&(FJ +0.0018[FJ2)~ ; f, f' and f” were taken from the International Tables for X-ray Crystallography.‘2 Fifteen peaks were located around the chlorine atom, which could be assigned as oxygen positions

data [Calc.(Found)] C

N

H

43.1(43.2) 41.8(42.2) 40.5(39.9) 42.7(43.2) 44.0(42.9) 40.5(40.3) 32.6(33.5) 35.5(36.2) 37.2(36.5) 32.6(32.9)

11.2(11.0) 10.8(10.9) 12.4(12.1) 11.8( 11.6) 11.6( 11.6) 9.9(9.8) 14.6(14.8) 13.8(13.8) 13.5(13.8) 11.7(11.5)

7.8(7.4) 7.6(7.7) 7.5(7.3) 7.8(7.6) 7.4(7.2) 7.3(7.2) 6.3(6.5) 6.8(6.8) 6.2(6.1) 6.1(6.2)

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Octahedral nickel(I1) complexes of the perchlorate ion, according to bond lengths ; six of them were assigned an occupancy factor of l/3 according to peak heights and the remaining nine were assigned an occupancy factor of 219. The position of all hydrogen atoms were computed and refined with an overall isotropic temperature factor, using a riding model, while the oxygen atoms were refined only isotropically, and the remaining non-hydrogen atoms anisotropically. The final R factor was 0.059 (wR = 0.062) for all observed reflections. Number of refined parameters = 356. Maximum shift/ESD = 0.2 in y of O(11) ; maximum and minimum peaks in final difference synthesis were 0.4 and -0.3 e A3, respectively. Crystal data for [Ni(DL-CTH)(Et,Dtc)](ClO,). weight = 590.88, CZ1H44N5S2NiC104, formula monoclinic, a = 19.551(4), b = 13.446(3), c = 11.428(3) A, /3 = 95.54(3)“, ?’ = 2990(2) A3, P2,/u, D, = 1.308 g cm-3, Z = 4, lr(OO0) = 1256, (Mo&) = 0.71069 A, ~(Mo-ZQ = 9.05 cm-‘, 298 K.

Physical measurements

IR spectra (400&200 cm-‘) were recorded as KBr pellets with a Beckman IR-20A spectrophotometer. UV-vis spectra were recorded in acetonitrile solutions with a Perkin-Elmer 550-S spectrophotometer. Voltammetric measurements were performed with the use of DACFAMOV 05-03 microcomputer controlled instrumentation with ohmic resistance compensation. ’ 3 Rigorously deareated acetonitrile (Carlo Erba) was used as a solvent and (n-Bu4N)PF6 (0.1 M) as supporting electrolyte. Solutions were deaerated by means of a stream of nitrogen for 10 min and a nitrogen blanket was maintained above the solutions during the electrochemical measurements. Potentials were referred vs an Ag/AgCl (0.1 M KCl) electrode separated from the bulk of the solution by a medium porosity disc. The potential for the one-electron oxidation of ferrocene is 420 and 460 mV vs the Ag/AgCl (0.1 M KCl) electrode with or without ohmic resistance compensation, respectively. A platinum wire auxiliary electrode was used in conjunction with a platinum discs working electrode (TACUSSEL ED1 rotating electrode, area 3.14 mm2). Electrochemical oxidations were performed in acetonitrile with a platinum electrode using the same DACFAMOV 05-03 instrumentation but working at 0.2 V above the E,,2. EPR measurements were recorded with a Brucker ER-200 spectrometer working at X-band frequency.

Fig. 1. Molecular structure of the [Ni(m-CTH)(Et,dtc)]+ cation. RESULTS

AND DISCUSSION

Description of the structure

The crystal structure of lNi(DL-CTH)(Et*Dtc)] (Clod) is formed from Clod- and [Ni(oL-CTH) (Et2Dtc)J+ units, the latter showing a distorted cisoctahedral geometry around the nickel(I1) ion. The structure of the cation is shown in Fig. 1, and the coordination environment of the nickel atom is shown in Fig. 2. Selected bond distances and angles are reported in Table 2. The two sulphur atoms of the dithiocarbamate ligand occupy two cis-equatorial positions of the inner coordination sphere of the metal ; the two Ni-S distances are 2.485(3) and 2.471(3) A, which compare well with the values [2.449(3) and 2.448(2) A] reported for the structure of the octahedral nickel-l, 1-dithio compound bis(phenyldithioacetate)bis(pyridine)nickel(II).3 These values are slightly longer than the same Ni-S distances

Fig. 2. Coordination environment of the nickel atom in the [Ni(oL-CTH)(Et,dtc)]+ cation.

1732

R. VICENTE

et al.

Table 2. Bond lengths and angles for C,3H26N5SZNi.C104 S( 1)-Ni S(2)-Ni N(ljNi N(4)--Ni N(8)--Ni N(l I)---Ni

2.471(3) 2.485(3) 2.174(10) 2.142(8) 2.197(9) 2.134(9) 1.705(11) 1.724(11) 1.475(14) 1.478(15) 1.472(16) 1.474(15) 1.486(15) 1.504(17) 1.483(17) 1.507(20) 1.548(18)

C(l5)_S(l) C(l5jS(2) C(2)--N(1) C(l4jN(l) C(3)-C(2) N(4jC(3) C(5)_N(4) C(5 1)--c(5) C(6>--c(5) C(7jC(6) C(7l)--c(7) S(2jNi-S( 1) N( ljNi-S( 1) N( 1jNi-S(2) N(4)--Ni-S( 1) N(4jNi-S(2) N(4jNi-N( 1) N(8jNi-S( 1) N(8jNi-S(2) N(8)---Ni-N( 1) N(8jNi-N(4) N( 1 I)---Ni-S( 1) N( 1 l)-Ni-S(2) N(lljNi-N(1) N( 1 I)-Ni-N(4) N(l l)--Ni-N(8) C(15jS(ljNi C( 15~S(2jNi C(2)--N( 1jNi C(l4jN(ljNi C(l4jN(l)--c(2) C(3w(2jN(l) N(4jC(3)--C(2) C(3jN(4)-Ni C(S)---N(4jNi C(5jN(4jC(3) C(5 1jC(5jN(4) C(6jC(5jN(4) C(6jC(5)--c(5 C(7tC(6)--C(5) C(7ljC(7jC(6)

1)

71.8(l) 102.9(3) 87.1(3) 164.3(3) 94.7(3) 83.7(4) 86.5(3) 101.8(3) 168.8(4) 88.7(4) 95.1(3) 165.4(3) 89.6(4) 99.1(4) 83.4(4) 86.4(4) 85.5(4) 105.2(8) 120.9(8) 112.0(10) 109.7( 11) 112.4(11) 102.5(7) 115.9(7) 114.7(10) 112.2(13) 110.7(11) 107.7(13) 118.9(13) 109.7(13)

in the square-planar nickel-l, 1-dithio derivatives (2.1-2.2 A), ‘5’ as a result of the high-spin nature of the nickel(I1) ion. The four nitrogen atoms of the CTH ligand occupy the two remaining equatorial and the two axial positions. The two axial bond distances, Ni-N( 1) and Ni-N(8) are slightly longer than the equatorial ones, suggesting that the coordination

1.599(20) 1.504(16) 1.511(15) 1.485(15) 1.509(14) 1.507(14) 1.539(17) 1.577(18) 1.546(17) 1.561(17) 1.521(17) 1.350(12) 1.490(14) 1.464(13) 1.486(15) 1.492(16)

WV-W’) N(8jC(7) C(9jN(8) C(lO>-c(9) N(1 l)--c(lO) C(12jN(ll) C(121)---C(12) C(13jC(12) C(l4jC(l3) C(141jC(14) C(142)-C(14) N(16jC(15) C(17jN(16) C(19jN(16) C(l8>--c(l7) C(20)---~(19)

WFW’)--c(71) N(8jC(7)-C(6) N(8jC(7F--C(7 N(8tC(7jC(72) C(7jN(8)---Ni C(9jN(8jNi

1)

C(9jN(8)--C(7) C(lO>--c(9jN(8) N(1 l>--c(lOjC(9) C(lOjN(ll)---Ni C(12jN(lljNi C(12)--N(IljC(10) C(121)-C(12jN(ll) C(13)--C(12jN(ll) C(13)--c(12)--C(121) C(l4>--c(l3jC(l2) C(l3)--c(l4jN(l) C(141)-C(14jN(l) c(141jc(14jc(13) C(142)-C(14jN(l) C(142jC(14jC(13) C(142jC(14)--C(141) S(2)--c(l5jS(l) N(16)-C(15jS(l) N(l6)--C(l5)--S(2) C(17jN(16+C(15) C(19jN(16jC(15) C(19 jN(16)---C(17) C(18)--C(17 jN(16) C(2OjC(19 jN(16)

105.4(13) 113.6(13) 110.7(13) 106.6(13) 120.6(8) 104.2(7) 112.7(11) 112.4(10) 107.9(10) 105.0(7) 116.5(7) 108.6(10) 110.3(11) 107.6( 10) 109.2( 11) 117.7(11) 112.1(11) 111.9(12) 105.3(12) 108.9(11) 111.5(13) 107.1(12) 116.0(6) 122.4(8) 121.6(8) 122.9(9) 120.7( 10) 116.5(9) 112.3(11) 110.8( 10)

polyhedron can be described as an elongated octahedron. The metal-nitrogen distances are in agreement with those of analogous &s-octahedral complexes of nickel(I1) with CTH. 14-‘* Mean values for C-S bond distances, C(15)-S(1) = 1.705(11) A and C(l5)---S(2) = 1.724(11) A, are slightly longer than in the case of bis(phenyldithiacetate)bis(pyridine)nickel(II)

1733

Octahedral nickel(H) complexes (1.68(l) and 1.69(l) A, respectively).‘3 The C(15) -N( 16) bond distance is equal to 1.350( 12) & a value in the range of the C-N bond values found in the literature for analogous dithiocarbamate compounds. ‘s2 Finally, it is important to underline that the Ni-S(2)-S( l)---N(4)-N( 11) plane is very di&ofieh. “r 0~ exam$jF. ‘$neX$@jl-@YJ~ a&e is 101.8(3)“, while N(8)-Ni-S(1) is 86.5(3)“; N(8)-Ni-N(4), 88.7(4)” and N(8)-Ni-N( 1l), 83.4(4)“. Moreover, the S(l)-Ni-S(2) angle is X+.&(?jYmucli lbwer clian ttie report&ival’ues t6r a square-planar environment in different bis(dithiocarbamato)nickel(II) complexes (between 78 a& “$.?~5” ‘Dti%S&&ar ‘$0‘Ge same a&e ‘ra 5% @her known ocZahebra> corn&x j32”>-3

nickel(I1) : 3A zs-+ 3T&9 and 3A2g-, 3T~,(P). The intense absorptions in the UV region, are typical of charge-transfer bands, similar to those observed in the analogous square-planar nickel(I1) compounds. ‘7’ The similarity of the visible spectra allows us to assume that the geometry of all the complexes must be very similar to j?Ii(DL~Y@%~,r;ir~~JKX&$ ~Bos~md~ec~ ‘W-ucruri~s known, i.e. distorted octahedral coordination around the nickel(I1) ion. Electrochemistry

The cyclic voltammogram hxeJXc, EX&,BXG a&i mrX%

for complexes with &3cWXv+0s&%&~n +2 YA &JE&gJ JZDl-&S iD fDE Y22gE sdiE~ .Q being reversible and the second being irreversible. This second irreversible cOuple occurs at II@ IR and electronic spectra potentials (over + 1.2 V). The remaining complexes IR spectra of the new complexes show the with AC, Tat and Etxant show only one irreversible v(N-H) bands at 2870 (m, sh), 2930 (s), 2970 (s) oxidation couple. Consequently, by replacing the sulpimi-&IT&- SlYiWK ?jy.I-rrcKetziilW~&?;-ua ozygerr a?,%?32388CL=-L~~~XG~zX-&X+~&i+K&WX s,* alWrr a? L%?&\‘s;; AZ%@ ts;: LB% {,m, &I s& 32% tsi‘ ifsGlmW~-~~~~&~Trerr~0? &&i-r~ti~~ WK& %XJ %%e2Xl’cnnl -i&ml $WiliuL&iXaIna%$ %y cnl -_’%YiW~Qi$fzinQi$i$ivzi~i~. A4tiihfd%&& ccentreb a1 J’lW Is, br~ar3) anr5 b2B IS>~JX-’ CDDZDXI LXYygEB~JL3DhD&‘EDz3&+), &YDhXB 23 _JZ’ih?2~ di&Ythepxsence ofthe CW4- anion. The v{--N) stret- ence in their electrochemical behaviour. The poscching bar~b is observed a1 15DDa& 14% LX-’ %Y jtiDDS Dj thefjrst CDU@k3, +%k u;ldth A?_& b.?h2~~3the dimelbyi and dielhyr dexivarives of Nil-CTH) sity ratio are shown in Table 4. A11 these new and at 1500 and 1490 err- ’ for the same Ni(Cyclam) complexes do not present any couple in the derivatives, respectively. These values indicate a reduction region (until -2 V). Instead, squarecertain amount of double bond character [v(CLN) planar starting complexes [Ni(DL-CTH)](CIOd),, = 169&1640 cm-‘; v(C-N) = 135&1250 [Ni(Cy)](ClO,), and [Ni(ditbiocarbamate)d undererr- ‘].2oFor the two ~i(macrocycle)Etxant](ClO,) go both reduction and oxidation processes in acefoG1ille..2’;13 In Fig. 3 one tup;l~> cj~f& v01CcomfieXes, banbs al 121D aDB )DSD cm ‘, cbaracteristic of the C-O-Cgroup2’ are observed. tammogram for these kinds of complexes is shown. Vis-UV spectra are summarized in Table 3. VisAfter controlled oxidation of these complexes, jble spectra are aL1very &I&L, .&owing weti defined the frQzenac&%X&YileQWlJLtiQ,S&n& pr@dzDXmj 6d and metal to ligand charge-transfer bands. signal in the EPR spectra. This feature may indicate Bands at 550-600 nm and 364-368 nm may be that this oxidation does not affect the nickel(I1) assigned to d-d transitions of the o&&e&al cation but only the organic part, which undergo a

Table 3. Electronic spectra of the new complexes in acetonitrile Compound

[Ni(C’W(A41(C104) [NW’WCWl(C104) [Ni(CTH)(Me,Dtc)](ClOJ [Ni(CTH)(Et,Dtc)](ClOJ [Ni(CTH)(PyrrDtc)](ClO.J [Ni(CTH)(Etxant)](ClO,) Wi(Cy)(Me~Dtc)l(Cl0~)

[Ni(Cy)(Et,Dtc)l(ClO,) [Ni(Cy)(PyrrDtc)l(ClO~) [Ni(Cy)(Etxant)](ClO,)

J (nm) 576 364 304(sh) 582 368 26O(sh) 276 245 596 278 248 595 273 246 598 300 595 276 242 558 276 244 556 272 242 558 300 238(sh) 552

212 220 208 2lO(sh) 208 225 208 214 208 220

R. VICENTE

1734

et al.

Table 4. Cyclic voltammetry (acetonitrile) Compound

W(CTWW(C~04) [Ni(CTH)(Tac)](ClO,) [Ni(CTH)(Me,Dtc)](ClO,) [Ni(CTH)(Et,Dtc)](ClO,) [Ni(CTH)(PyrrDtc)](ClO,) /Ni(CTH)(Etxant)](ClO,)

Fri(Cy)(Me,Dtc)l(Clo,) [Ni(Cy)(Et,Dtc)l(C10,) ~i(Cy)(PyrrDtc>l(C10,) [Ni(Cy)(Etxant)](ClO,>)

1200

0

-1200

Type

El,,

I I R R R I R R R I

1.0 1.0 0.686 0.506 0.574 0.900 0.507 0.375 0.484 0.805

Width

Rel.

0.076 0.074 0.070

1.04 1.05 0.93

0.067 0.070 0.072

1.13 1.08 1.13

Acknowledgements-Financial assistance from the CICYT (Grant No. MAT88-0545) and from ACCION INTEGRADA HISPANO-ITALIANA No. 49, area 02 (1989) are acknowledged. Supplementary Material Available. A listing ofall bond distances and angles, final atomic coordinates, anisotropic thermal parameters, hydrogen atom coordinates and observed and calculated structure factors.

REFERENCES -5 800

600

E(mV)

Fig. 3. Cyclic voltammogram of [Ni(rn-CTH)(Me,dtc)] (ClO,) in acetonitrile solution (10m3 M) with 0.1 M (Bu,N)PF, as electrolyte support (scan rate 0.1 V s- ‘).

polymerization process, giving diamagnetic species. We can conclude, consequently, that if there is for-

mation of organic radicals, these are unstable, even at low temperature.

1. D. Coucouvanis, Prog. Inorg. Chem. 1970,11,233. 2. D. Coucouvanis, Prog. Znorg. Chem. 1979,26, 301. 3. M. Bonamico, G. Dessy, U. Fares, A. Flamini and L. Scaramuzza, J. Chem. Sot., Dalton Trans. 1976, 1743. F. P. Emmenegger, Znorg. Chem. 1989,28,2210 and refs therein. A. M. Bond and R. L. Martin, Coord. Chem. Rev. 1984,54, 23. R. P. Burns, F. P. McCullough and C. A. McAuliffe, Adv. Znorg. Chem. Radiochem. 1980,23,211. (a) F. Curtis, D. A. Swann and T. N. Water, J. Chem. Sot. 1973, 1963 ; (b) B. Bosnich, M. L. Tobe and G. A. Webb, Znorg. Chem. 1965, 4, 1109 ; (c) L. G. Warner and D. H. Busch, J. Am. Chem. Sot. 1969, 91, 4092.

CONCLUSIONS New types of l,l-dithio complex of nickel(II), with only one sulphur bidentate ligand and octahedral coordination, are synthesized and characterized by spectroscopic and X-ray measureshow an unusual ments. These compounds electrochemical behaviour : no reduction processes are present in the range 0 to - 2 V, but one reversible couple appears between 0.375 and 0.686 V for the complexes with the R,N-CS,ligands. Attempts to obtain stable compounds by controlled oxidation were unsuccessful.

8. C. Benelli, A. Dei, D. Gatteschi and L. Pardi, Znorg. Chem. 1988,27,2831. 9. A. M. Tait and D. H. Busch, Znorg. Synth. 1976, 18,4. 10. P. Main, S. E. Fiske, S. L. Hull, L. Lessinger, G. Germain, J. P. Leclerc and M. M. Woolfson, MULTAN, An automatic system of computer programs for crystal sructure determination from X-ray diffraction data. University of York, U.K.; University of Lovain, Belgium (1984). 11. G. M. Sheldrick, SHELX, A computer program for crystal structure determination, University of Cambridge, U.K. (1976). 12. International Tables for X-ray Crystallography, Kynoch Press, Birmingham (1974).

Octahedral nickel(I1) complexes 13. P. Cassoux, R. Dartiguepeyron, P. L. Fabre and de Montauzon, L’Actualiti Chimique 1985, 79; Cassoux, R. Dartiguepeyron, P. L. Fabre and D. Montauzon, Electrochim. Acta 1985, 11, 1485. 14. N. F. Curtis, D. A. Swann and T. N. Waters, Chem. Sot., Dalton Trans. 1973, 1408. 15. P. 0. Whimp, M. F. Bailey and N. F. Curtis, Chem. Sot. A, 1970,1956.

D. P. de J. J.

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18. H. Ito, K. Sugimoto and T. Ito, Bull. Chem. Sot. Jpn 1982,55,1971. 19. P. W. G. Newman and A. H. White, J. Chem. Sot., Dalton Trans. 1979,2239 and refs therein. 20. A. C. Fabetti, F. Forghieri, A. Giusti, C. Preti and G. Tosi, Spectrochim. Acta 1984, &IA, 343. 21. M. L. Shankaranarayana and C. C. Patel, Spectrochim. Acta 1965, 21, 95. 22. D. C. Olson and J. Vasilevskis, Znorg. Chem. 1969, 8, 1611. 23. F. V. Lovecchio, E. S. Gore and D. H. Busch, J. Am. Chem. Sot. 1974,%, 3109.