J. CHEM. SOC. DALTON TRANS. 1994 11154,6- D i met hyl pyri mid i ne-2-t hionato (d mpymt - ) Complexesof Nickel(ii) and Cadmium(ii). Crystal Structure of[Cd(dmpymt),]: a Compound with a Calixarene-likeStructure tRosa Castro,B Jose A. Garcia-Vazquez,B Jaime Romero,a Antonio Sousa,Q,a Robin Pritchardand Charles A. McAuliffeba Departamento de Quimica lnorganica, Universidad de Santiago, 15706 Santiago de Compostela, SpainDepartment of Chemistry, University of Manchester, Jnstitute of Science and Technology, PO Box 88,Manchester M60 IQD, UKNickel and cadmium complexes of the anionic form of 4,6-dimethylpyrimidine-2-thione (Hdmpymt) andtheir adducts with neutral ligands (1.1 0-phenanthroline or 2,2'-bipyridine) have been prepared by anelectrochemical procedure and characterized by spectroscopic (IR, UV, 'H and 13C NMR) methods, and forthe [{Cd(dmpymt),},] complex by X-ray crystallographic techniques.This compound is hexanuclear withan array of six cadmium atoms bridged by twelve sulfur atoms. Each cadmium atom has a distorted-octahedral cis-CdS,N, environment with each ligand acting in a N,S bidentate S-bridging mode. Thehexamer has a calixarene-like structure with cavities large enough to accommodate molecules such asacetonitrile, carbon monoxide and molecular iodine.It is well known that metal thiolate complexes adopt variousnuclearities and great structural complexities. These features arethe result of the tendency of thiolate ligands to bridge metalcentres to yield oligo- or poly-meric species. These aggregationphenomena may be limited by providing steric constraints byappropriate ligand design or introducing coligands to block anumber of co-ordination sites.Thus, for example, the 4,6-dimethylpyrimidine-2-thione (Hdmpymt) copper(1) complex ishexanuclear, [{Cu(dmpymt)},], with all coppers in a distorted-octahedral geometry; ' the pyridine-2-thione (Hpyt) complex[ C d ( ~ y t ) ~ ] is polymeric and that with 3-trimethylsilylpyridine-2-thione (Hspyt) is d i m e r i ~ , ~ [{Cd(~pyt)~)~]. An analogoussituation has been found previously in [Ni(~pyt)~],~ [{Cu-In this paper we report the electrochemical synthesis andcharacterization of a series of complexes of nickel(r1) andcadmium(I1) with 4,6-dimethylpyrimidine-2-thione, a com-pound which, besides having methyl groups that might modifythe degree of aggregation as a result of steric constraints, is oneof the most versatile sulfur donors since it can act, as in the caseof pyrimidine-2-thione, as (a) a neutral monodentate ligand co-ordinated via the sulfur atom ' (A) or as a chelate * (B), and (b)as an anionic ligand, in which case it can be monodentatethrough the sulfur atom' (C), chelating" (D) or bridgingbetween two (E)9*'1 and (F) or three' (G) metal atoms co-ordinated by both nitrogen and sulfur atoms.The complex[{Cd(drnpymt),),] is the first reported in which pyrimidine-2-thione links two metal atoms in the form F.(SPYt)),l and C{Zn(sPYt)2)21.6ExperimentalAcetonitrile, 4,6-dimethylpyrimidine-2-thione, 1,l O-phenan-throline and 2,2'-bipyridine were used as supplied (Aldrich).Supplementary data available: The atomic positions, full lists ofbond lengths and angles and other crystallographic data have beendeposited at the Fachinformationszentrum Karlsruhe, Gesellschaftfur Wissenschaftlichtechnische Informationen, 76344 Eggenstein-Leopoldshafen, Germany.Any request for this material should quote afull literature citation and the reference number CSD 57468.M MA 6I I M M M MC D EM M M M MF GThe metals (Ega Chemie) were used as plates (ca. 2 x 2cm).Electrochemical Syntheses.-The electrochemical methodused in the synthesis of the metal complexes is similar to thatdescribed by Tuck and co-workers.'2 The cell consists of a tall-form beaker (100 cm3) containing an acetonitrile (50 cm3)solution of 4,6-dimethylpyrimidine-2-thione and a smallamount of tetraethylammonium perchlorate (ca.10 mg) as thesupporting electrolyte; a platinum cathode and the sacrificialanode (nickel or cadmium), attached to a platinum wire, servedas the electrodes and were connected to a d.c. power supply. Forthe synthesis of mixed-ligand complexes, either 1,10-phenan1116 J. CHEM. SOC. DALTON TRANS. 1994throline or 2,2'-bipyridine was added to the electrolyte phase. Inall cases, hydrogen evolved at the cathode. These cells can besummarized as Pt( -)(MeCN + Hdmpymt(M( +) and Pt( -)IMeCN + Hdmpymt + LJM( +) where M is nickel or cadmiumand L represents I , 10-phenanthroline or 2,2'-bipyridine. Whenneither 1,lO-phenanthroline nor 2,2'-bipyridine was present,precipitation took place within ca.15 min of the start of theelectrolysis and continued throughout the experiment. The solidwas collected, washed with acetonitrile and diethyl ether anddried in uacuo. When I , 10-phenanthroline or 2,2'-bipyridinewas present, as the electrolysis proceeded, the colour of thesolution changed from pale brown to red-brown for nickel andto orange for cadmium. A black product was formed on thecathode but no effort was made to identify it. After theelectrolysis the solution was filtered to remove any solidimpurities and the solvent evaporated in a Rotavapor to givean oil, which was treated with diethyl ether to produce a solid.The solution compositions and experimental conditions aregiven in Table 1.Physical Measurements.-Microanalyses were performedusing a Carlo-Erba EAllO8 microanalyser.The analytical dataare given in Table 2. The IR spectra were recorded in KBr mullson a Perkin Elmer I80 spectrophotometer, solid reflectancespectra on a Perkin Elmer Lambda 9 spectrophotometer.Magnetic measurements were taken using a SQUID magneto-meter. Proton NMR spectra were recorded on a Bruker WM 250MHz spectrometer using (CD,),SO as solvent; chemical shiftswere determined against SiMe, as internal standard.Crystal Structure Determination of [{Cd(dmpy~nt)~}~].-Crystal data. C9,Hs,Cd6N,,Sl ,,-A4 = 2687.05, rhombohedral(hexagonal axes), space group R3(h) (no. 148), a = 18.784(6),c = 32.13(1) A, U = 9819(6) A3, Z = 3, D, = 1.363 g ~ m - ~ ,F(OO0) = 4005, h(Mo-Kx) = 0.710 69 A, p = 11.86 cm '.Data collection and processing. A colourless trapezoid ofapproximate dimensions 0.20 x 0.15 x 0.05 mm was mountedin a Lindeman glass tube in the presence of mother-liquor.Allmeasurements were made on a Rigaku AFC65 diffractometerwith graphite-monochromated Mo-Ka radiation. Cell constantsand an orientation matrix for data collection (obtained from aleast-squares refinement using the setting angles of 19 carefullycentred reflections in the range 6.76 < 28 < 14.86") corre-sponded to a rhombohedral (hexagonal axes) cell.The data were collected at room temperature using the 0-28scanning technique to a maximum 28 value of 50. I". Omegascans of several intense reflections, made prior to datacollection, had an average width at half-height of 0.39" with atake-off angle of 6.0".Scans of (1.31 + 0.30 tan 0)" were madeat a speed of 4.0" min-' (in a).Of the 3685 reflections collected, 3423 were unique (Rin, =0.039 1). An empirical absorption correction applied using theprogram DIFABS resulted in transmission factors rangingfrom 0.77 to 1.33 The data were corrected for Lorentz andpolarization effects.Structure solution and refinement. The structure was solved bydirect methods. l4 The non-hydrogen atoms were refinedanisotropically. Hydrogen atoms were included in the structure-factor calculation in idealized positions. The final cycle of full-matrix least-squares refinement was based on 923 observedreflections [ I > 20(Z)] and 205 variable parameters andconverged to R = E(IFoI - lFc~)/Z~Fol = 0.073, and R' =[Cw(lF,I - IF,1)2/Z:wlFo12]* = 0.074.The standard deviation ofan observation of unit weight was 2.10. The weighting schemewas based on counting statistics and included a factor (p =0.03) to downweight the intense reflections. Plots of C(lFoI -IF,[), versus lFol, reflection order in data collection, (sin o)/h,and various classes of indices showed no unusual trends. Themaximum and minimum peaks on the final Fourier differencemap were to 0.55 and -0.67 e 8, ,, respectively.Neutral atom scattering factors were those of Cromer andWaber; ' corrections for anomalous dispersion effects werethose of Cromer. l 6 All calculations were performed using theTEXSAN crystallographic software package.Additional material available from the Cambridge Crystallo-graphic Data Centre comprises H-atom coordinates, thermalparameters and remaining bond lengths and angles.Results and DiscussionThe thiolate complexes, [M(dmpymt),] (M = Ni or Cd), andtheir adducts with 1,lO-phenanthroline (phen) and 2,2'-bipy-ridine (bipy), [M(dmpymt),(phen)] or [M(dmpymt),(bipy)],are easily prepared in good yield by the simple one-stepelectrochemical method described, in keeping with previouswork on related system^.'^^.'^*'^The electrochemical efficiency, defined as moles of metaldissolved per Faraday of charge, was found to have an averageof 0.5 k 0.02 mol F-' for nickel and cadmium, irrespective ofthe presence or absence of neutral ligand.These results,together with the evolution of hydrogen at the cathode, arecompatible with the occurrence of the following electrodereactions (1)-(3) where M = Ni or Cd and L = bipy or phen.Cathode: 2 Hdmpymt + 2 e- - H, + 2 dmpymt- (1)Anode: 2 dmpymt- + M ---- [M(dmpymt),] + 2 e- (2)2 dmpymt- + M + L-+ [M(dmpymt),L] + 2 e- (3)In the case of [Cd(dmpymt),], crystals suitable for X-raydiffraction studies could be isolated. However, these deterioratedin a short time, and had to be prepared immediately prior tobeing mounted for data collection.Structure of[(Cd(dmpymt),),].-The molecular structure of[{Cd(dmpymt),},] is shown in Fig. 1, together with the atomicnumbering scheme adopted. For clarity, a view of the co-ordination sphere of the metals is shown in Fig.2, Final atomiccoordinates, selected bond distances and angles are listed inTables 3 and 4. The structure contains discrete molecules havinga crystallographically imposed symmetry with three moleculesin the unit cell.The structure consists of a regular non-planar hexagon of sixTable 1 Experimental conditions for the electrochemical syntheses aAmount of bipyCompound or phen (8)[Ni(dmpymt),].2.75H20[Ni(dmpymt)2(bipy)]-1 .5H20 0.18[Ni(dmpymt),(phen)]. l.5H2O 0.22[Cd(dmpymt),(bipy)]-0.5H20 0.18CCd(dmpymt),(phen)I.H 2 0 0.23CCd(dmpymt),lInitialvoltage (V)313022151617Metaldissolved (mg)66.963.566.2130.0125.3130.0E'lmol F-'0.510.480.500.520.500.52a 0.3 1 g Hdmpymt + ca.20 mg NEt,CIO,. Voltage required to produce a current of 20 mAJ . CHEM. SOC. DALTON TRANS. 1994 1117~~~Table 2 Analytical data * for the complexesAnalysis (%)Compound Colour C N H[Ni(dmpymt),]*2.75H20 Green 37.1 (37.3) 14.0 (14.5) 4.7 (5.0)[Ni(dmpymt),(bipy)]. Green 50.5 (50.8) 15.8 (16.2) 4.5 (4.8)1.5H20[Ni(dmpymt),(phen)]. Brown 52.8 (52.9) 15.4 (15.4) 4.5 (4.5)1.5H20CCd(dmpymt),l White 37.4 (36.9) 14.0 (14.3) 4.0 (3.6)[Cd(dmpymt),(bipy)]- Yellow 47.7 (47.5) 14.6 (15.1) 4.6 (4.4)0.5H20[Cd(dmpymt),(phen)]. Yellow 49.0 (48.9) 14.0 (14.3) 4.0 (4.1)H2O* Calculated values given in parentheses.PFig. 1 Perspective view of the structure of [{Cd(dmpymt),),] PFig. 2 Perspective view of the co-ordination sphere of the metals inC{Cd(dmpy mt), 161cadmium atoms bridged above and below by the sulfur atoms oftwelve thiolate anions.These sulfur atoms belong to two sets ofsix, each (see Fig. 2) being approximately planar, with threeatoms above the best least-squares plane ( + O . 114 A) and theTable 3with estimated standard deviations (e.s.d.s) in parenthesesFinal fractional atomic coordinates for [{ Cd(dmpymt),),]X0.169 3(1)0.059 l(4)0.300 3(4)0.028( 1)0.184(2)0.295(2)- 0.089(2)-0.007(2)- 0.137(2)- 0.104( 3)-0.019(2)- 0.225(2)0.018(2)0.255(2)0.260( 3)0.189(3)0.146( 2)0.299( 2)0.063( 2)-0.190(3)- 0.174(5)- 0.047(4)0.262(6)0.193(5)0.1 12(6)0.182(5)0.1 3 1 (6)0.043 8Y0.447 4( 1)0.478 3(5)0.529 3(4)0.366( 2)0.3 7 5( 2)0.380(2)0.425( 2)0.399( 2)0.3 1 O(2)0.268(2)0.303(2)0.287(2)0.264(2)0.435(2)0.352(4)0.288(3)0.30 1 (2)0.335(2)0.241 (2)0.5 19( 3)0.503(4)OSOO(4)0.62( 1)0.594(5)0.547(5)0.564( 5 )0.5 50(6)0.519 5L0.669 71(7)0.711 5(2)0.718 6(3)0.656(1)0.681( 1)0.729 3(7)0.777(1)0.683( 1)0.653( 1)0.628( 1)0.632( 1)O.654( 1)0.606( 1)0.746( 1 )0.793( 1)0.783(1)0.749(2)0.827( 1)0.728( 1)0.880( 2)0.887(2)0.879(2)0.837(4)0.852(3)0.862(3)0.81 l(3)0.8 15(4)0.845 6other three below it (-0.114 A).These planes are parallel toeach other and also to the best least-squares plane defined bythe six cadmium atoms (maximum deviation 0.098 A) which liesin the middle of the sulfur atom planes, with a dihedral anglebetween them of 0".The Cd - - Cd distances in the hexamericrings are all cu. 3.716 A, showing that no significant cadmium-cadmium interactions exist in the compound.Each cadmium atom is co-ordinated to one nitrogen atomand the bridging sulfur atom of two 4,6-dimethylpyrimidine-2-thionate ligands, and to other two bridging sulfur atoms fromtwo ligands bound to other cadmium atoms. Therefore, eachligand acts as a bridging [N,(p-S),] five-electron donor ligand.Each cadmium atom is in a distorted-octahedral environment,CdS,N,, with the two nitrogens in cis position; the anglesdefined by two trans atoms and the cadmium atom,S( 1)-Cd-S( 1 '), S( 1 1)-Cd-N( 1) and S( 1 1 ')-Cd-N( 1 1) havevalues of 168.0(2), 154.7(8) and 161.3(7)", respectively, insteadof the required 180". The bond angles between cadmium andthe adjacent atoms of the chelate rings have values lower than90°, 60.4(8) and 61.0(7)", whereas the angles involving the othercis atoms of different ligands have values larger than 90", in therange 102(1)-90.5(2)0.These values deviate greatly from thetheoretical and result in distortion of the octahedral geometry.The Cd-S distances are also slightly different. Thus, in thering Cd,S, defined by cadmium and bridging sulfur atoms thereare three Cd-S bond distances in the range 2.638(8)-2.666(8) Aand one at 2.761(8) A, as in other six-co-ordinated compoundswith Cd,S, units; for example, in polymeric bis(pyridine-2-thionato)cadmium(Ir)' and bis(benzothiazo1e-2-thionato)-cadmium(I1) the distances between cadmium atoms and sulfurbridge atoms lie in two groups, but contrary to [{Cd-(dmpymt),),], there are two Cd-S bonds in each group.In[{Cd(dmpymt),},] the shorter bond lengths are close to thosefound in the above complexes, 2.543(5) and 2.649(4) A for[Cd(pyt),] and 2.547(4) and 2.606(4) A for [Cd(bztt),].However, in this compound the longer Cd-S bond lengths aremuch shorter than those found in [Cd(pyt),], 2.809(4) and3.038(4) and in [Cd(bztt),], 3.061(5) and 3.129(4) A. Moreover1118 J. CHEM. SOC. DALTON TRANS. 1994-P, Table 4 Selected interatomic distances (A) and angles (“) for [{Cd-(dmpymt), } 61Cd( 1 )-S( 1) 2.76 1 (8) N( 1 1)-C( 1 1) 1.33(3)Cd( 1 )-S( 1 ’) 2.666(8) N(11)-C(15) 1.42(4)Cd( 1)-S( 1 1 ”) 2.638(8) N(12)-C(13) 1.29(4)Cd( 1)-S( 1 1) 2.665( 8) N(12)-C(11) 1.35(4)Cd( 1 )-N( 1 ) 2.36(2) C(3)-C(4) 1.47(4)Cd( 1)-N( 1 1) 2.38(2) C(3)-C(6) 1.49(4)S( 1 1)-C( 1 1) 1.76(3) C(5FC(7) 1.49(4)N( 1 )-C(5) 1.31(3) C( 13)-C( 16) 1.44(4)N(2)-C(3) 1.41(4) C( 15)-C( 17) 1.55(4)S( 1 )-C( 1) 1.66(3) C(4tC(5) 1.40(4)N( 1 )-C(]) 1.39(3) C( 13)-C( 14) 1.31(4)N(2)-C( 1 ) 1.37(3) C( 14)-C( 1 5 ) 1.46(5)S( 1)-Cd(1)-S(1‘) 168.0(2) Cd(1)-N(l1)-C(l1) 104(3)S( 1)-Cd( 1)-S( 1 1) 99.5(2) Cd(l)-N(ll)-C(15) 141(3)S(1)-Cd(1)-S( 1 1”) 90.5(2) C( 1 1 )-N( 1 1)-C( 15) 1 15(3)S(lkCd(1)-N(1) 60.4(8) C( 1 1)-N( 12)-C( 13) 1 1 5(3)S( 1 )-Cd( I)-N( 1 1) 90.9(6) S( 1)-C( 1)-N( 1) 1 16(3)S( 1 ’)-Cd( 1 )-S( 1 1) 92.1(2) S( 1)-C( 1)-N(2) 122(3)S(1‘)-Cd(1)-S(1 1”) 90.8(2) N( 1)-C( 1)-N(2) 122(3)S( 1’)-Cd( 1)-N( 1) 107.6(8) N(2)-C( 3)-C(4) 123(3)S(1’)-Cd(1)-N(1 1) 91.6(6) N(2)-C(3)-C(6) 1 13(4)S(11)-Cd(1)-S(l1”) 100.4(3) C(4tC(3)-C(6) 124(4)S(l l)-Cd(l)-N(l) 154.7(8) C(3FC(4)-C(5) 1 13(3)S( 1 1)-Cd( 1 )-N( 1 1) 6 1.0(7) N( 1 )-C(5FC(4) 1 24( 3)S( 1 1 ”)-Cd( 1 )-N( 1 ) 95.3(7) N(1 )-C(5tC(7) 121(3)S(11”)-Cd(1)-N(l1) 161.3(7) C(4)-C(5)-C(7) 1 15(4)N(1)-Cd(1)-N(l1) 102(1) S( 1 1)-C( 1 1)-N( 11) 1 12(3)Cd(1)-S(1)-Cd(1”) 86.4(2) S(l l)-C(ll)-N(l2) 120(3)Cd( 1 )-S( 1 )-C( 1 ) 81(1) N(l1)-C(l1)-N(l2) 128(3)Cd(1”)-S(1)-C(1) 106(1) N( 12)-C( 1 3)-C( 14) 129(4)Cd(1)-S(ll)-Cd(I’) 88.9(2) N( 12)-C( 1 3)-C( 16) 1 1 9( 5 )Cd(1)-S(I l t C ( l 1 ) 82(1) C( 14)-C( 1 3)-C( 16) 1 12(5)Cd( 1 ‘)-S( 1 1 )-C( 1 1) 1 1 5(3)Cd(1)-N(1)-C(1) 103(2) N( 1 1)-C( 15)-C( 14) 1 19(3)Cd(1)-N(1)-C(5) 136(2) N(ll)-C(l5)-C(l7) 112(4)loo( 1) C( 1 3)-C( 14)-C( 15)C( 1 )-N( 1)-C(5) 12 l(3) C( 14)-C( 15)-C( 17) 130(4)C(l)-N(2)-C(3) 116(3)(’) Denotes + x - y , 4 + x, - z and (”) y - 4, 4 - x + y , - z.both lengths in the complex are longer than those found in[Cd(pymt),(phen)],” 2.588(3) and 2.549(3) 8,, but are similarto those found for terminal Cd-S bonds in other octahedralcadmium(I1) complexes, 2.647-2.777 8,.OP2The Cd-N bond distances, 2.36(2) and 2.38(2) A, are slightlyshorter than those found in octahedral cadmium(I1) compoundscontaining the pyrimidine-2-thionate moiety, [Cd(pymt),-(phen)],” 2.42(2) and 2.53(2) A, but they are very close to thoseobserved in other octahedral cadmium(r1) complexes involvingother heterocyclic nitrogen-donor ligands, for example 2.343(4)8, in [Cd(~yt),],~ 2.306(4) 8, in [Cd(bztt),],, 2.376(3) A indiaquadiformatobis(nicotinamide)cadmium(n) 2 3 and 2.35 A inCdCl2-2py (py = ,~yridine).,~Each of the pyrimidine rings is planar, but the sulfur atoms lieout of the plane of pyrimidine to which they are bound [by 0.03 18, for S( 1) and 0.104 8, for S( 1 1 )].The interplanar angle betweenthe pyrimidine ring of ligands bound to the same metal is only9” whereas the rings of ligands bonded to adjacent cadmiumhave interplanar angles in the range 73-82’. The solventacetonitrile molecules do not interact with the cadmiumcomplex in any significant manner and there are no noteworthyintermolecular contacts.Comparison of this structure with those of cadmium withpyridine-2-thione and 3-trimethylsilylpyridine-2-thioneshows that an increase of the steric constraint produced by thesubstituents on the ligand modifies drastically the structure ofthe isolated complex.So, the cadmium complex with pyridine-2-thione has a polymeric structure with a cadmium bonded tofour bridging sulfur and two nitrogen atoms. In this case theFig. 3 Space-filling representation of the crystal structure ofCPWmpymt), 163ligands act as double bridges, type F, and the pyridine ringsbonded to the adjacent cadmium atoms are almost perpen-dicular to each other. The increased steric constraint introducedby the methyl groups in the case of 4,6-dimethylpyrimidine-2-thione reduces the polymerization and the compound is ahexamer. When the case of 3-trimethylsilylpyridine-2-thione,which has a more voluminous substituent, is considered, it isfound that the complex is a dimer, where each cadmium atomhas a five-co-ordinate environment, being bonded to a terminalthree-electron-donor ligand (D) and to two bridging sulfuratoms and one nitrogen of two five-electron-donor bridgingligands (F).This steric property shows well that the extent ofaggregation can be tuned by careful control of the stericdemand imposed on the thiolate ligands. Naturally, otherfactors, such as reaction conditions, solvent nature, etc., canalso play a role.It is noteworthy that the hexamer is positioned on acrystallographic 3 site, which generates a triangular, sulfur-richcalixarene-like well on either side of the molecule.Disorderedacetonitrile guest molecules are clearly associated with theabove cavities (see Fig. 3), which are also sufficiently large toaccommodate alternative guest molecules such as acetylene,carbon monoxide and molecular iodine.Vibrational Spectra.-The IR spectrum of Hdmpymt exhibitsa band in the range 3200-3060 cm-’, attributed to v(N-H).,~This band is absent in the spectra of the nickel and cadmiumcomplexes, indicating that the ligand is in the thiolate form. Avery strong band around 1620 cm -’ for the ligands, assigned tov ( W ) and v(C=N) of a non-aromatic ring, is shifted to lowerwavenumbers, in the range 1570-1 580 cm-’, for the complexes;this is further confirmation of the thiolate form of the ligands.Besides these bands, the mixed-ligand complexes show bandstypical of co-ordinated 2,2’-bipyridine (ca.770 and 740 cm-’) 26and 1,lO-phenanthroline 2 6 3 2 7 (ca. 151 0, 850 and 725 cm-’).NMR Spectra.-The ‘H NMR spectrum of 4,6-dimethyl-pyrimidine-2-thione in (CD,),SO shows a broad singlet at6 13.49 assignable to NH. This signal is absent in the NMRspectra of the cadmium compounds, further conformation ofdeprotonation of the ligand during the electrolysis process. Thespectra of the complexes (Table 5 ) show a singlet at 6 6.60 dueto the H5 proton and a singlet at 6 2.21-2.10 due to the methylgroup; this shows that at room temperature both methylgroups are chemically equivalent.This equivalency is observeJ. CHEM. SOC. DALTON TRANS. 1994 1119Table 5 Proton and carbon-13 NMR data for cadmium(1r) complexes *H'H 3cCompoundHdmpymt* Relative to tetramethylsilane.r~dmpynit -6.62 (s) H52.24 (s) N4'g6'6.60 (s) H52.14 (s) H4'*6'6.60 (s:) HS2.11 (s) H4'96'6.60 (s) Hs2.20 (s) H4'*6'8.72 (d) H6s6'8.43 (d) H393'8.00 (m) H4,4'7.52 (m)H5*5'9.16 (d) H2v98.79 (d) H4*78.20 (s) H5v68.03 (m) H3*'dmpymt -181.2 C2109.8 C5181.6 C2165.4 C4*6112.5 C5181.8 c2165.5 C4.6112.6 C522.6 C4's6'22.6 C4'v6'165.5 C4v6112.7 C522.6 C4'g6'Phen(biPY)153.2 C2149.2 C6138.5 C5125.0 C3121.2 c4149.8 C2139.1 C4b139.1 C4129.0 C4a127.2 C5125.2 C3Table 6complexesElectronic spectroscopic and magnetic data for nickel(I1)Compound ?/cm-' PlPB[Ni(dmpymt),]-2.75H2O 9950, 11 100, 16 130 3.6[Ni(dmpymt)2(bipy)].1.5H20 10 000, 11 360 (sh), 16 950 3.8[Ni(dmpymt),(phen)]-1.5H2O 10 530, 11 500 (sh), 16 130 3.1in the '"C NMR spectra where only a signal assigned to bothmethyl groups is seen around 6 22.5.However, the structure of [(Cd(dmpymt),),] shows thatthe methyl groups should be non-equivalent.It is tentativelyproposed that the observed equivalency at room temperatureis due to a fluxional behaviour. Such behaviour could bedemonstrated by using variable-temperature NMR experi-ments in the case of complexes of p~rirnidine-2-thione.'~Unfortunately, the poor solubility of our complexes inchloroform and similar solvents precludes such studies.The NMR spectra of the mixed-ligand complexes[Cd(dmpymt),L] show additional signals due to co-ordinated2,2'-bipyridine and 1,l O-phenanthroline.28 Consequently anoctahedral monomeric structure can be suggested for them.Similar structures have been found by X-ray diffraction analysisfor [Zn( pyt),( phen)] or [Cd(pymt),( phen)] . 'Mugnetic Moments und Electronic Spectra.-The diffusereflectance spectra of the nickel complexes (Table 6) show bandsin the ranges 9900-10 550 (vl) and 16 100-16 950 cnir' (v,).These are very similar to the ranges found for other nickelcomplexes with similar ligands, the structures of which havebeen shown to be octahedral by X-ray diffraction ana1ysis.l8Consequently, these bands can be attributed to 3T2, t- 3A2g(vl) and 3Tlg(F) - 3A,, (vJ transitions in an octahedralfield.,' The clearly discernible shoulder observed for vl, at11 000-1 1 500 cm-', reflects the distorted-octahedral geometryof these complexes.No band attributable to the 3T1,(P) - 3A2g (v,) transition is observed, probably because it is very* We thank a referee for bringing this point to our attention.weak and obscured by a strong charge-transfer band in theregion 25 000-32 000 cm-'.The magnetic moments of the nickel complexes lie in therange 3.1-3.8 pB at room temperature. 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