1973 1945Co-ordination Complexes containing Multidentate Ligands. Part IILXThe Visible Spectra of Some Five-co-ordinate Nickel(ii) Complexes con-taining Tris(o-dimethylarsinopheny1)stibine. Trigonal Bipyramidal andSquare Pyramidal ComplexesBy Livio Baracco, Michael 7. Halfpenny, and Charles A. McAuIiffe," Department of Chemistry, Universityof Manchester Institute of Science and Technology, Manchester M60 1 ODThe trisubstituted stibine. tris(o-dirnethy1arsinophenyl)stibine (sbta) reacts with nickel(tt) salts to form com-plexes of type [Ni(sbta)X]Y (X = CI, Br, I, NCS, and NO,; Y = CI. Br, I, CNS, NO,, and BPh,) and [Ni(sbta),]Z,(Z = CIO, and BPh,). These diamagnetic complexes are five-co-ordinate, the [Ni(sbta)X]+ species being trr-gonal bipyrarnidal while the [Ni(sbta),J2+ species are square pyramidal.The visible spectra of these complexesare discussed and compared with those of other complexes containing ligands with the SbAs, and As, donor sets.As part of a study of the stabilisation of metal-antimonybonds by chelation 2-5 we have paid particular attentionto tris (o-dimethylarsinophen yl) stibine (sbt a) because ,as well as producing stable metal-stibine bonds, a numberof other interesting facets of ' tripod ' ligands and theircomplexes can be examined.These tripod ligands have been extensively studiedand generally they form trigonal bip yramidal complexes,6but some interesting structural differences have beenobserved for differing ligands. From X-ray studiesit is thus apparent that when the apical and equatorialdonor atoms are linked by o-phenylene chelate chainsthe equatorial atoms are above the metalbut when a three-carbon chelate backbone such as thetrimethylene chain is employed the equatorial donorsare below the metal atom,1° This, of course, is a conse-quence of the inability of the two-carbon and three-carbon chains to provide for an apical-metal-equatorial(L'-M-L) angle of 90"; for the two-carbon case theangle L'-M-L <go", and for the three-carbon caseLL'-M-L >90°.11.12 This has been reflected in thevisible spectral behaviour of the trigonal bipyrarnidalnickel(x1) complexes formed by the (o-Ph,P*C,H,)L' (L'= P, As, and Sb) ligands, where it was found that asthe apical donor atom, L', was changed in any seriesof complexes an anomalous spectrochemical series forL' was obtained, viz., P > As < Sb in contrast tothe spectrochemical order R,P > R3As > R3Sb foundfor complexes of the unidentate ligands R3L.13 Thiseffect was attributed to compression of the apicalL'-Ni bond upon complexation.In this study we havefurther examined this phenomenon.EXPERIMENTALTris(o-dimethylarsinophenyl)stibine, sbta, was preparedPreparation of the CowzpZexes.--[Ni(sbta)X]X (X = C1,as described.bPart 11, W. E. Hill, J . Dalton, and C. A. McAuliffe, J.C.S.Dalton, 1973, 143.2 B. K. Higginson, C . A. McAuliffe, and L. M. Venanzi,I9zovg. Chim. Acta, 1971, 5, 37.3 B. R. Cook, C . A. McAuliffe, and D. W. Meek, Inorg. Chem.,1971, 10, 2676. * C. A.McAuliffe and D. W. Meek, Inorg. Chim. Acta, 1971,5, 270.6 L. Baracco and C . A. McAuliffe, J.C.S. Dalton, 1972, 948.6 M. J. Norgett, J. H. M. Thornley, and L. M. Venanzi,Co-ord. Chem. Rev., 1967, 2, 99.Br, I, NCS, a@d NO,) and [Ni(sbta),](ClO,),.-WhenNiXZ,6H,O (0-0021 mol) in ethanol (15 ml) was added to astirred solution of the ligand (1.33 g , 0.002 mol) in ethanol(20 ml) under nitrogen a deep blue-purple colour wasimmediately formed. The mixture was refluxed for 1 hand then allowed to cool in the refrigerator. Intenselycoloured crystals were deposited during 3-7 h. Thesewere filtered off and recrystallised from CH,CI,-EtOll.Yields were ca. 70%. From [Ni(sbta)X]X the complexes[Ni(sbta)X]BPh, (X = Cl, Br, I, NCS, and NO,) wereobtained by metathesis (see Table 1).Physical Measurements.-Magnetic susceptibilities weremeasured by the Gouy method.Conductivity measure-ments were carried out with a Cambridge InstrumentsLtd. conductivity bridge. 1.r. spectra were measured inNujol or hexachlorobutadiene mulls on a Perkin-Elmer62 1 spectropfiotometer, and electronic spectra on a Beck-man DK2 spectrophotometer (for reflectance spectraBaSO, was used as a diluent).RESULTS AND DISCUSSIONWe have applied the method of Feltham andHayter l4 to determine the electrolyte-type of theNi(sbta)X, and Ni(sbta) (X)BPh, complexes in nitro-methane; we found that when A, - A, was plottedagainst 2 / c slopes of 160-230 -lcm2 equiv.-l mol-4 1iwere obtained, a good indication that the complexesare 1 : 1 electrolytes and may be formulated [Ni(sbta)X]Xand [Ni( sbt a) X] BPh,, respectively .Further evidenceof co-ordinated and unco-ordinated anions can be ob-tained from the CNS- and NO3- complexes. In the[Ni(sbta) (NCS)]CNS complex v(C5N) absorptions can bedistinguished in the i.r. spectrum at 2098 and 2050cm-l, assignable to co-ordinated Ni-NCS and unco-ordinated CNS- groups, re~pective1y.l~ Further evidence7 T. L. Blundell, H. M. Powell, and L. M. Venanzi, Ckem.* L. P. Haugen and R. Eisenberg, Inorg. Chew., 1969,8,1072.9 G. A. Mair. H. M. Powell, and L. M. Venanzi, PYOC. Chem.Comwt., 1967, 763.SOC., 1961, 170.1967, 89, 3424.10 D. L. Stephenson and L. F. Dahl, J . Amer. Chenz. Sac.,11 C. A. McAuliffe. D.Phil. Thesis, Oxford, 1967.J.W: Dawson, B. C. Lane, R. J. Mynst, and L. M. Venanzi,l3 P. L. Goggin, R. J. Knight, L. Sindellari, and L. M. Venanzi,l4 R. D. Feltham and R. G. Hayter, J . Chem. SOG., 1964,l5 J. L. Burmeister, Co-ord. Chem. Rev., 1966, 1, 206, andInovg. Ghzm. Acta, 1971, 5, 25.Inorg. Chim. Acta, 1971, 5, 62.4587.references thereinJ.C.S. Daltonof Ni-NCS co-ordination is provided by the occur-rence of bands attributable to v(CS) and S(NCS) a t832 cm-l and 433 cm-l respectively.le Similarly astrong i.r. absorption at 1370 cm-l for [Ni(sbta) (NO,)]-BPh, is indicative of co-ordinated nitrate.17 That theligand co-ordinates via all three -AsMe, groups in the[Ni(sbta)X]+ complexes is suggested by the appearanceof only one resonance at ca.7 8-3 in the lH n.m.r.spectra of the complexes, although fast exchange be-tween co-ordinated and unco-ordinated -AsMe,. groupscannot be excluded. The free ligand exhibits oneresonance attributable to -AsMe, groups a t T 8-80.Compound[Ni(sbta)Cl]Cl[Ni(sbta)Cl]BPh,[Ni(sbta)Br]Br[Ni (sbta) BrIBPh,[Ni (sbta) I] I[Ni(sbta) IIBPh,[Ni(sbta) (NCS)]CNS[Ni(sbta) (NCS)]BPh,[Ni (sbta) (NO,)]NO,[Ni(sbta) (NO,)]BPh,[Ni(sbta),](CIO,),"i(sbta) 21 (BPh4) 2Table 2 contains a comparison of the ligand-field bandsin a series of trigonal bipyramidal [Ni(ligand)X] + coni-plexes. The ligands are (o-&~e2As*C6H,),L' L = As 2oand Sb) and (Me,As*CH,*CH,*CH,),L' (L' = As 21 andSb 21). For the complexes of ligand backbone o-C,H,the Sb complexes absorb at higher energy than the Ascomplexes , while for ligand backbone -CH,*CH,*CH,-when X = C1, As < Sb, but when X = I, As > Sb,with X = Br being a fairly intermediate case.Thiscan be explained by the L'-M-L angle of less than 90".The equatorial donors are lifted out of the plane and a tthe same time the apical donor is compressed on to theTABLE 1Some physical properties and analytical data of the nickel(r1) complexes aColourDeep blueDeep blueBlue-purpleDeep blueBlackPurple-blackDeep blueDeep blueDeep blueDeep blueBlue-purpleBlue-purplcM.p./"C241-246204-205225-227207-2092072082 04203-205203-2052 05215215Analyses (yo)Carbon HydrogenCalc. Found Calc. Found38.4 36.0 3.8 4.353.4 53.4 4.7 4.832.7 32.9 3.4 3.851.4 51.4 4.5 4.629.6 28.8 3-1 3.249-1 48.1 4.3 4.237.2 37.4 3.6 3-663.6 52-6 4.6 4.834.1 34-7 3.9 3.852.3 52.0 4.6 4.636.2 35.9 3.8 4.256.8 57.1 3.5 3.7OtherCalc. Found9.1 9.1 bElectronic absorption spectra,Solution c18,360(2620), 23,950(220),30,700(2970)29,85O(sh)30,200(3500)18,000(2150), 23,500(65),17,450(3525), 23,250(735),1 9,400 (3 150), 24,250 (605)18,850(1365), 31,00O(sh), 5icni-lSolid18,050,23,55018,700,24,40017,200,23,250,19,200,24,05018,700a All the complexes are effectively diamagnetic with a small T.I.P.contribution. b Halogen. c In dichloroethane ; extinctioncoefficients/l mol-1 cm-l in parentheses. d Nitrogen. 6 Nickel.The electronic spectra are in Table 2.The spectraare characterised by two absorptions at ca. 18 k K and23 k K . These are indicative of trigonal bipyramidalgeometry la and not square pyramidal geometry.lgThe two absorptions can be assigned to the one-electrontransitions between the orbitals e' --+- a' (ca. 18 k K )and e" _t a' (ca. 23 k K ) in a system of C,, symmetry.There is also a band which occurs at ca. 30 kK, itsfrequency and intensity varying with the co-ordinatedanion. This may be assigned to metal-arsenic or-antimony charge transfer.As the co-ordinated anion on the z-axis is changedthis would be expected to affect the a' level (d-orbitalof character z2) the most, and hence both the e'+a' and e'' + a' transitions will vary, though since thee r r level contains d-orbitals of character xz and yx thislevel, too will be affected and so the e r r + a' transi-tion energy shift is difficult to predict. However, itit can be seen that both transitions change in theorder NCS- > NO3- > C1- > Br- > I, i.e., a regularspectrochemical series. It may be noted that the highenergy of the NCS- complex absorption is furtherevidence of Ni-NCS co-ordination.l6 A.Turco and C. Pecile, Nature, 1961, 191, 66.N. F. Curtis and Y . M. Curtis, Inorg. Chem., 1965, 4, 804.G. Dyer, J. G. Hartley, and L. M. Venanzi, J . Chem. SOC.,C. A. McAuliffe and D. W. Meek, Iizorg. Chew., 1969, 8, 904.1966, 1293.metal atom. As the size of the apical donor increasesso does this compression, resulting in an increasedligand-field strength.Thus the (o-Me,As*C,H,),S bligand exerts a stronger field than does (o-Me,As*C,-H,),As. On the other hand, the L'-M-L angle in the'rABLE 2Factors affecting ligand-field strengths of triarsine-stibine ligands in [Ki(ligand)X]+ complexesXc1BrINCSc1BrIChelate backboneo-C~H,o-C,H~o-C6H4o-C,H4-CH,*CH,.CH,--CH2*CH2*CH2--CH2CH2CH,-A S17,50023,30017,30023,10016,80022,70018,80023,50016,56016,05015,670Sb18,35023,95018,00033.60017,55023,25019,40024,260> 16,400 - 16,130< 16,950trimethylene ligand case is greater than 90" and nocompression of the apical donor on to the nickel takesplace. Thus for complexes [Ni(ligand)X]+ with the(Me,As-CH,~CH,*CH,),L', the L' = As ligand should20 0.St. C. Headley, R. S. Nyholm, C. A. McAuliffe, L. Sindel-lari, M. L. Tobe, and L. M. Venanzi. Inorg. Chim. Acta, 1970, 4,93.*l G. S. Benner and D. W. Meek, Igtovg. Chem., 1967, 6, 13991973 1947have visible absorption bands at higher energy than forL' = Sb, since the normal ligand-field strength isR3As > R3Sb.12 However, from point (2) above wefind that the comparative energies of the visible bandsare a function of the halogen donor as well as the apicalAs or Sb donor. Thus, As > Sb for X = C1, As - Sbfor X = Br, but As < Sb, for X = I. This nephel-auxetic behaviour can be explained in terms of thepolarisability of the halide donors compared with thatof the apical donor^.^^^^Thus it can be seen that the effect which chelatingligands have on the structure and spectrochemistry ofthe resulting complexes can be a function of chelatechain length just as much as it can be a function of thenature of the donor atoms.Also, even when chelatechain length is constant in a set of similar ligands thennephelauxetic behaviour may well become importantwhen the donors are polarisable.We have briefly reported22 on the reaction betweennickel@) perchlorate hexahydrate and sbta. Afterthe reactants are mixed in ethanol deep blue crystals of[Ni(sbta),] (ClO,), are soon deposited. Metal : ligandratios of 1 : 1, 1 : 2, and 1 : 3 all lead to the formationAs( I 1 A 5of the same product. Addition of NaBPh4 to a solu-tion of [Ni(sbta),](ClO,), leads to quantitative pre-22 L.Baracco, M. T. Halfpenny, and C. A. McAuliffe, Chem.23 C. Furlani, Co-ovd. Chew. Rev., 1968, 3, 141, and referencesComm., 1971, 1602.therein.cipitation of [Ni(sbta),] (BPh,),. The visible spectrain solution exhibit one band at 20.1 kK (E = 2300)(C10,- complex) and 19.9 kK (E = 2050) (BPh,- com-plex); both of these bands exhibit a shoulder at lowerfrequencies. The position of these bands indicatesthat the [Ni(sbta)d2+ cation is essentially square pyra-midal 193 23 and not trigonal bipyramidal.l**2* Hencein this five-co-ordinate complex the most likely typeof ligand co-ordination must involve a structure similarto (I), i.e., a square pyramidal complex containinga terdentate and a bidentate sbta ligand. It is in-conceivable that the co-ordination could involve aquadridentate and a unidentate ligand, as it is notpossible for sbta to chelate as a quadridentate ligandto a metal in a square pyramidal configuration.The formation of [Ni(sbta),}(C1O4), with a tripodligand containing heavy donor atoms may be con-trasted with the usual stoicheiometry obtained fromthese ligands and Ni(H,O),(CIO,)Z, vix., [Ni(L)(ClO,)]-C10 L = qp or qas 18) or [Ni(L)(H,O)](ClO,), {L =pta: or qa; 21 qa = tris(3-dimethylarsinopropy1)ar-sine). The stability of the [Ni(sbta),I2+ cation, whichcontains the novel [Ni(Sb,As,)12+ donor set, must beconsiderably greater than either [Ni(sbta) (ClO,)] + or[Ni(sbta) (H,0)I2+, as the bis-ligand complex forms nomatter what metal : ligand ratio is used in the reaction.Also, it is interesting that one ligand, sbta, can formtwo types of five-co-ordinate complex with nickel@),the trigonal bipyramidal [Ni(sbta)X]+ and the squarepyramidal [ Ni (sbt a) 2] 2+.We thank the Leverhulme Trust and the S.R.C. forPostdoctoral Fellowships (to L. B. amd M. T. H. re-spectively).[2/1603 Received, 7th JuZy, 1972124 G. S. Benner, W. E. Hatfield, and D. W. Meek, Inorg.C h e w , 1964, 3, 1544