9 Zinc Cadmium and Mercury By I.6. GORRELL School of Chemistry and Molecular Sciences University of Sussex Falmer Brighton BNlgQJ UK 1 Introduction This chapter summarizes results published in the literature during 1995. Porphyrins and phthalocyanines are not included. Zinc cadmium and mercury have been covered in reviews on intermolecular co-ordination in organometallic compounds,' developments in the chemistry of derivatives containing NC,H,(CH(SiMe,)}-2 NC,H,(C(SiMe,),)-2 and related ligands, and precursor chemistry for the deposition of 11-VI semiconductor^.^ A major reference work which covers the organometallic chemistry of these elements has also appeared. 2 Zinc X-Ray diffraction studies of nearly 40 organozinc compounds have been re~iewed.~ The co-ordination geometry of divalent zinc cations has been investigated using the crystal structures of small molecules containing this cation found in the Cambridge Structural Database and by ab initio calculations on [Zn(H,0),]2'*rnH,0 (n = 1-6 rn = 0-2).The results were compared to those obtained for beryllium and magnesium.6 Carbon-donor ligands A 13C solid-state NMR study of I3CO in zeolite Zn-Y and on ZnO led to the observation of a zinc carbonyl species.' Electrolysis of CF,Br in dmf using zinc or cadmium anodes yielded MBr(CF,) and M(CF,) (M = Zn Cd); the mechanism of these reactions was discussed.8 Matrix-isolated MH(Me) (M = Zn Cd Hg) obtained in reactions of excited metal atoms with methane have been studied using IR ~pectroscopy.~ Density-functional methods and force-field calculations have indicated regular helical structures for a series of gaseous cyanide anions [M,(CN),,+ '1-(M = Zn Cd; x = 1-27) formed by laser ablation of M(CN),." An ab initio study of the mechanism of the aminoalcohol-promoted reaction of dialkylzinc compounds with aldehydes has appeared.' Nitrogen- and phosphorus-donor ligands A series of monomeric four-co-ordinate zinc complexes [ZnR(HB(bpz),)] and 113 114 I.B. GorrelI Fig. 1 Crystal structure of K[ZnMe(Bu'NCH=CHNBu')]-thf (Reproduced by permission from J. Chem. Soc. Chem. Commun. 1995 1839) [ZnR( HB(dmpz),)] (R = Me Et) has been prepared from thallium hydroborates and ZnR,. The three-co-ordinate derivatives [ZnR{ H,B(bpz),)] (R = Me Et But) and the hydride [ZnH( HB(bpz),)] were similarly prepared.Reactivity studies led to the isolation of [ZnX{HB(bpz),)] (X = O,CH O,CMe C,Ph SH OSiMe, CN N, NCS C1 Br I) C(zn(~-oH)CH2B(bpz>,l),l CZn(?2-0,CMe)(H,B(bpz)2)] and [ZnR(HB(OR')(bpz),)] (R' = Me Et Pri). Several compounds including [Zn(HB(dmpz),),] were crystallographically characterized.' The reaction of [MeZn(Bu'N=CHCH(NBu')CH(NBu')CH=NBu')ZnMe]with potassium in thf afforded K[ZnMe(Bu'NCH=CHNBu')]*thf a linear polymer of alternating cations and anions (Fig. l).' A series of phosphaallyl complexes [M(RNPNR'),] (M = Zn Cd; R = SiMe, R' = C6H2BU',-2,4,6; M = Zn R = R' = C6H,Pri,-2,6 Bu'; R = C6H4Pri-4 R' = C6H,Bu',-2,4,6; R = c6H,Bu',-2,4,6 R' = Bu' adamantyl) and [in((2,4,6-Bu',C6H,)NPPj(C,H,But3-2,4,6))Me] have been prepared and character- ized.' A mixture of CuI and ZnI in pyridine gave crystals of [Cuo~,,Zno~081,(py),]~2py which contained a square-planar arrangement of pyridines with axial iodides.' A quasi-octahedral co-ordination sphere of two trans imidazolium nitrogen atoms and four square-planar water molecules has been found in a zinc complex of 3-(imidazol-5- yl)prop-2-enoic acid molecules were linked by hydrogen bonding.I6 The structure of [Zn(bipy),][ClO,] has been determined.17 A distorted-tetrahedral environment was found for the metal centres in [MCl,L,] (M = Zn Cd; L = creatinine;18 M = Zn L = anta~oline'~), [ZnCl,(C,H,N,),] in which the zinc centres were bonded to N(7) of the purine ligands,,' and [Zn(C,,H 1N20,),(NH3)2]~0.5H,0 zinc being co- ordinated to two deprotonated diphenylimidazolidine-2,4-dionatoligands and two ammines.,' The preparations of ZnX,L [L = N,N'-ethylenebis(pyrrolidin-2-one); Zinc Cadmium and Mercury X = NO, C1 Br I] ZnX,L (X = ClO, BF,) Cd2(N03),L3 and Cd(NO,),L,-H,O have been reported and several were characterized by X-ray crystallography.22 A series of zinc complexes containing the dithiosquarate ligand and a bidentate nitrogen base have been prepared and characterized and some photophysical properties reported., Reaction of Zn(NO,) with (EtO,C),CC(SK) (K,L) and en gave [Zn(L)en] which has been studied using spectroscopic conductivity and magnetic measurement~.~~ A polymeric chain was present in [Zn(C,H,NCO,),] in which trans L-prolinato ligands bonded through nitrogen and one carboxylate oxygen with a fifth site occupied by the other oxygen of a neighbouring molecule.25 Reaction of lY2,4-1H-triazole (HL) with ZnC1 in EtOH gave [ZnCl(L)] in which each metal ion was surrounded by three nitrogen atoms from different ligands and a chloride.Each ligand was simultaneously bonded to three different zinc atoms through its three nitrogen atoms leading to the formation of polymeric chains.26 Reaction of K[Zn(CN),] ZnC1 and py in aqueous solution yielded [Zn(py),][Zn(CN),] with a polymeric structure of alternate arrays of tetrahedrally and octahedrally co-ordinated zinc atoms bridged by cyanide ligand~.,~ A quartz-like net structure was observed for [ZnAu,(CN),] in which each silicon atom was replaced by zinc and each Si-0-Si link by Zn-NC-Au-CN-Zn.28 The crystal structure of [Zn(4,4'-bipy),(SiF6)]n*xdmfshowed squares with zinc at the corners and 4,4'-bipy along the sides.These two-dimensional networks were connected along the c axis by bridging anions.29 The crystal structure of [Zn(CN)(NO,)L,,,] [L = 2,4,6-tris(4-pyridyl)-1,3,5-triazine] revealed two identical interpenetrating three-dimen-sional nets each composed of cages made up from six [Zn(CN)(NO,)] squares linked by eight L units.30 The reaction of [M{N(SiMe,),},] (M = Zn Cd) with Bu',P(E)NHR (E = Se Te; R = Pri C6Hl1) gave the monomeric and sublimable complexes [M{ Bu',P(E)NR),]; the mixed-ligand compounds [Zn{ N(SiMe,),}(Bu',P(E)NR}] were also prepared.,' Metallation of Ph,PH with ZnEt (5:3) in thf produced [{Zn(p-PPh,)(Et)},(HPPh,),(thf)] which contained a Zn,P ring.32 The 1:1 reaction of ZnR (R = Me Et Pri Bun Bu' CH,SiMe,) with (Me,Si),PH yielded [ZnR{P(SiMe,),}].The compounds were dimeric or trimeric depending upon the size of R in the solid state and in solution; [Zn{ C(SiMe,),}{ P(SiMe,),}] was monomeric.33 Likewise reaction of ZnR (R = Me Et CH,SiMe,) with AsH(SiMe,) yielded [ZnR{ As(SiMe,),}] which crystallized as dimers or trimers again depending upon the size of R., Reaction of ZnC1 with Ph,PSiMe and PR'R2 (R' = Ph R2 = Et; R' = Me R2 = Pr"; R' = R2 = Bun) gave [Zn,Cl,(PPh,),(PR'R2,),] and of ZnC1 with PhP(SiMe,) or Bu',PSiMe in thf yielded [Zn,Cl,(PhPSiMe,),(thf),l or [{ZnCl(PBu',)},] respectively. All were crystallographically characterized.35 Oxygen-donor ligands Electrochemical oxidation of zinc in a solution of 1-methylimidazoline-2-thione(HL) in MeCN gave [Zn,OL,] containing a central oxygen bonded to a tetrahedral array of zinc atoms with six bridging thionato ligand~.,~ The alkyl carbamates [M,R,(0,CNEt,)6] (M = Zn R = Me Et; M = Cd R = Me) have been prepared and characterized. The crystal structure of [Zn,Me,(O,CNEt,),] [Fig. 2(a)] revealed a planar array of zinc atoms whereas [Zn,Me,(O,CNEt,),] [Fig. 2(b)] formed by its reaction with ZnMe, contained a tetrahedral arrangement of zinc atoms.37 The magnetic and spectroscopic properties of a series of complexes [M3L6(H20)6]- 116 I.B. Gorrell t Fig. 2 Crystal structures of (a)[Zn,Me,(O,CNEt,),] and (b)[Zn,Me,(O,CNEt,),] (Reproduced by permission from J.Chem. SOC. Dalton Trans. 1995 1043) X,*xH,O (L = 3-methyl-4-phenyl-l,2,4-triazole, X = CIO, M = Zn x = 0; M = Cd x = 5; X = BF, M = Zn Cd x = 0) have been in~estigated.~~ The zinc centres were trigonal bipyramidal in the dimer [Zn2(C3H50,),(C6H6N20),] with two bidentate bridging and one monoden tate propionate ligands and two apical nicotinamide ligand~.~' The crystal structure of [Zn(C,0,)(OH,),(dmso)2] revealed extended chains of zinc squarate linked by hydrogen bonds to form a layer structure. At 25-100 "C in aqueous solution conversion to the known three-dimensional cage network Zn(C,O,)(OH,) o~curred.~'An X-ray crystallographic study has shown that the pyridone oxygen atom bridges pairs of zinc atoms to form Zn,O units which in turn Zinc,Cadmium and Mercury are linked by N,N’-p-phenylenebis(rnethylenepyridin-4-one)(L) bridges forming com- plex arrays of 34- and 38-membered rings in [Zn,L4][BF,]4-4H,0.41 The crystal structure of NaA,[Zn,{ H(CO,),)(CO,),(H,O),] (A = K Rb) revealed two-dimen- sional Zn,(H(C0,),}(C03),(H20)2 layers with zinc in a distorted trigonal-bi-pyramidal geometry.42 The syntheses and structures of two new carbamates of zinc [Zn(O,CNEt,),(tmen)] and [Zn,Me(O,CNEt,),(py)] have been reported.43 The 4-cyanopyridine complex of zinc crotonate was dimeric with square-pyramidal zinc whereas the vinylpyridine complex was polymeric with five-co-ordinate zinc.44 The zinc centres in [Zn(PhCO,),(tu),] and [Zn(OAc),(OC(NH,),),] adopted a distorted tetrahedral ge~metry.~’.~~ The crystal structure4’ of the nitroacetophenonato com- plex [Zn{(ON(0)CHC(Ph)O},(py)2] and the synthesis48 of [ZnCl (EtO2CCH,N(H)CH,CO2}(H20)]have been reported.Aerosil (colloidal silica) has been shown to react with ZnMe to give Zn(0Si)Me and SiMe surface structure^.,^ The geometrical structures of Zn(NO,) aqueous solutions over a wide range of concentrations have been determined using EXAFS spectros- copyso and hydrolysis of Zn” in OSm~ldm-~ NaX (X = NO, C1 ClO,) gave [Zn(OH)] in all three media but Zn(OH),(aq.) only in perchlorate solution^.'^ + Sulfur-and selenium-donor ligands A severely distorted square-pyramidal geometry was adopted by the zinc centre in [{ Zn(c,H,S,)(bipym)),].One sulfur atom of the benzenedithiolate ligand bridged the metals while the second was terminally bound.’ The organic conductors Let],- [MM’(SCN),] (M = K Rb Cs; M’ = Co Zn Cd) have been prepared and some crystallographically characterized. Resistivities were also rep~rted.’~ Reaction of KCS with Zn(acac) or CdC1 followed by addition of [PPh,]Cl gave [PPh4]- [M(CS,),] (M = Zn Cd).54 The crystal structures of [Zn(SPh),( 1-mim),] and “Me,] -[Zn(SPh),(l-mim)] and their reactivity with (MeO),PO has been reported. The relevance of these results to the DNA methylphosphotriester repair site in Escherichia coli Ada was disc~ssed.~~ The structures of [(Zn(SBu‘)Me),] and its py and tmta adducts have been reported and their potential as precursors to ZnS disc~ssed.’~ The use of ZnMe and propylene sulfide to grow ZnS layers has been reported.57 Zinc powder was found to react with sulfur in donor solvents solv to give [ZnS,(solv),] [solv = tmen lmim 4-(dimethylamino)pyridine].The structure and reactivity of the tmen complex were rep~rted;’~ ZnS,-tmen has been used as a polysulfide-transfer reagent in the preparation of 1,2-Se,S,.59 The reaction of [Zn(N(SiMe,),),] with 2,6-(2,4,6-Me,H,C6),c6H,seH in hexane yielded the diselenolate with a linear geometry at zinc; recrystallization from thf gave the adduct which contained planar three-co-ordinate zinc.,’ Treating [Zn-{N(SiMe,),) ,] with [TeH(C,H Me,-2,4,6)] yielded [{ Zn[Te(C,H Me,-2,4,6)] )n] which on reaction with 1 equivalent of PMe gave the 1 1 adduct while an excess of Lewis base (PMe, 1-mim py dmpe) gave tetrahedral adducts.Heating these complexes led to the formation of cubic ZnTe.6’ Reactions of [MSe,12- with TePEt to give [MTe,Se,-,]’- (M = Zn Cd Hg; n = 0-4) have been investigated using 77Se and 125Te NMR and the crystal structure of [PPh,][Hg(Te,Se,),] has been deter- mined.62 The syntheses crystal structures and 125Te NMR spectra of [PPh,] [M(Te4)J (M = Zn Cd Hg) have been reported.63 A variety of bi- tetra- penta- and hexa-metallic compounds of general formula LnM(SePh),L (Ln = Eu Sm Yb; 118 I.B. Gorrell M = Zn Hg; L = py thf; x = 4 10 12; y = 3 4 6 7) have been prepared and structurally characteri~ed.~ Halogen-donor ligands Energies geometries force constants vibrational frequencies and dipole moments have been calculated for the free molecules MX MX and M,X and the solids M,X (M = Zn Cd Hg; X = F C1 Br I)using relativisticdensity-functional methods.65 The crystal structure66 of [NMe,][NEt,][ZnCl,] and the synthesis and structural chara~terization~~ of [H2L] [ZnCl,]*H,O (HL = 4,6-dimethyl-2-sulfanylpyrimidine) have been reported.Thermal decomposition of the latter yielded [ZnCl,(HL),] and [ZnL,]. The structure of [H,L][ZnBr,] (L = 4,6-diamino-2-methylsulfanyl-pyrimidine) showed anion tetrahedra hydrogen bonded to the cations.68 An X-ray powder diffraction and IR spectroscopic study of the hydrogen bonding in [Zn(NH,),]X (X = Br I) has been published6’ and reaction of PhP(S)(NMeNH,) with ZnC1 yielded the 1 1 adduct which gave polymetallic compounds on condensa- tion with aldehydes.70 3 Cadmium Carbon-donor ligands The zeolite-mimetic host clathrate [NMe,.xG][Cd,(CN),] showed highest inclusion selectivity for ethylbenzene from mixtures of ethylbenzene and xylene isomer^.^ The polymorphic behaviour of a series of Cd(CN) host clathrates has been discussed in terms of the geometry and functionality of the guest molecules.72 The clathrate Cd(CN),CCl has been studied using extended-Huckel tight-binding calculation^.^^ Donor-free Cd(CF,), which can act as a source of difluorocarbene has been obtained from CdEt and CF,I at -40°C.74 The crystal structures of [Cd(cp),L] (L = tmen pmdien) showed that the hapticity of the cyclopentadienyl ligand changed from q2 in the tmen complex to q1 in the pmdien complex.75 Nitrogen- and phosphorus-donor ligands X-Ray analysis of [CdMe,(dabco)] revealed a polymeric structure with cadmium in a distorted-tetrahedra1 en~ironment.~~A crystallographic study of [Cd(C,H,NO,S),(NH,),] revealed octahedral cadmium centres with square-planar ammines and axial saccharinato groups bonded through nitrogen.77 X-Ray crystallo- graphy showed that [Cd(en),][Ni(CN),] contained discrete ions whereas [CdNi(CN),].2H2N(CH,),NH,.rnH,O (n= 2-7 9; rn = 0-2) was constructed by catenation of ammine or [Ni(CN),] -units or both linking octahedral cadmium atoms.78 The [Ni(CN),12 -anions in [Cd(Hdabco)][Ni(CN),],-4NH2Ph acted as bidentate ligands between the cations along the a and c axes to form a two-dimensional network.Two monodentate (Hdabco) groups were axially co-ordinated to cadmium and the aniline molecules were hydrogen bonded to give an inclusion c~mpound.~’ Reaction of [Cd {N(SiMe,),) ,] with LiPPh yielded [Li( thf),] ,[Cd,(PPh,) J a crystallographic study of which showed an adamantane-like anion.80 Oxygen-donor ligands Reaction of Cd(BH,) with MOR (M = Li R = Et Bu‘ Ph mes; M = Na R = Bu‘) Zinc Cadmium and Mercury led to the formation of either addition products [Cd(BH,),(OR)] or ligand exchange to give [Cd(BH,)(OR)]. The model compound [CdMe(OBu')] was tetrameric in the solid state. With [Cd(OC6H,Me,-2,4,6),] Cd(BH,) gave [Cd(BH,)(OC,H,Me,- 2,4,6)].81 Reaction of Riecke cadmium with benzoquinone in thf yielded [Cd(C6H4O2'-)(thf),][C6H,O2'-] or ([Cd(C,H,O,'-)(thf),] + [C6H402'-]}.The radical anion was either symmetrically or asymmetrically co-ordinated to the The cadmium centres were pentagonal bipyramidal in [Cd(C,H,NCO,),(H,O)] which formed a polymeric network in which each nicotinate anion acted as a bidentate chelating carboxylate ligand to one cadmium and also bonded through nitrogen to a second cadmium.83 The crystal structure of polymeric tetraaquabis(ma1onato)di-cadmium showed six- and eight-co-ordinate cadmium atoms which were correlated with 'I3Cd NMR chemical shifts at 6 18 and -107 respe~tively.~~ Pyrazolylborate cadmium carboxylates were found to form 1 1 complexes with epoxides and subse- quent epoxide-carboxylate coupling provided epoxide oligomers with terminal ester groups.85 Cadmium complexes containing the betaine ligand triphenylphosphonio- propionate [{Cd[Ph,P(CH2)2C02],X}2]Y2 (X = NO, Y = NO, ClO,; X = C1 Y = ClO,) have been prepared and shown to possess a centrosymmetric tetrakis(p carboxylato-0,O')dimetal core.86 Sulfur- and selenium-donor ligands A new three-dimensional structure for a cadmium thiolate [Cd{ SCH,CH(OH)CH,OH},] has been publisheds7 and the structures of [Cd{ S,P(C,H 1)2}2]2CHC13 and its PBu' adduct and [{ Cd[S,P(OC,H ,),],),] have been determined.88.89 The preparation characterization and thermolysis of Cd(SR) (R = Pr' Bu' CH,Ph) Cd(SPr'),*l-mim and [(Cd(SCH,Ph),},].l-mim have been reported," as has a double-layer superlattice structure built up of [Cd3,S,,{SCH,CH(OH)CH3}36]~4H20 cl~sters.'~Layers of CdS have been grown from CdMe and propylene s~lfide.'~ Irradiation of CdS powder suspended in ethereal solutions of organolithium compounds LiR yielded cadmium and R via a radical mechanism.' Halogen-donor ligands The anions in 4,4-oxydianiliniumg4 and 4-nitroaniliniumg5 tetrachlorocadmates contained corner-sharing octahedra.The structure of 2-methylpentane-1,5-di-ammonium tetrachlorocadmate revealed layers of CdCl corner-sharing octahedra in a perovskite-like structure. Electronic and thermal properties were also reported.96 The crystal structures of [CuCl([ 14]aneN4)],[CdC1,] and [Cu([14]aneN4)]-[CdCl,(H,O),]Cl have been determined.97 The structures of [H2L][Cd,C1,(H,O),] and [HL'] [Cd3Cl,,(H,0)] (L = N,N'-dimethylpiperazine L' = N-methylpiperazine) both contained anion chains with cadmium atoms six-co-ordinate in the former and five- and six-co-ordinate in the latter.98 Reaction of 4,6-dimethyl-2-sulfanylpyrimidine (HL) with CdC1 yielded [CdL(OH)] and { [H,L][CdCl,]},; the latter contained face- sharing CdC1 ~ctahedra.~' The crystal structure of [C ,H7N,0][CdBr,].2H,0 indicated that the water was hydrogen bonded between the ions.'00 The structures of the tetramethylpyrazinium salts [C,H,,N,][CdI,]~nH,O (n = 0 3) revealed hydro- gen bonding involving either anions and cations (n = 0) or cations only (n = 3).'01 120 I.B. Gorrell 4 Mercury A theoretical study of mercury-photosensitized reactions has suggested the initial formation of exciplexes followed by insertion of Hg* into a reactive X-H bond (X = H CH, C,H, SiH,) giving ultimately X radicals and H atoms.'02 Carbon-donor ligands The structural data on more than 320 organomercury compounds has been reviewed.lo3 Weak Lewis acid-base interactions exist between the mercury centres and the halogen atoms in dimeric [{HgPh(CBrCl,)),].The angle at mercury is 179".'04 Reaction of HgC1 with o-lithio-(S)-( -)-dimethyl( 1-phenylethy1)amine gave (S)-[HgCl(C ,H,CH(Me)NMe,)] which contained a non-planar metal stereocentre. The bromide and iodide were isostructural. lo' The ylide Ph,PCHCOPh with HgX (X = C1 I) in MeOH yielded the centrosymmetric dimer [{HgX,[PhOCCHPPh,]},] (chloride as MeOH solvate). '06 The synthesis and thermal transformations of complexes of [Hg(Ge(CF,),},] with o-quinones have been reported."' A crystal structure revealed Hg-C 0 bonds in Hg(C,H,Bu',-1,2,4) prepared by sodium- amalgam reduction of the [BiC1(C5H,Bu',-1,2,4)] analogue.'" The formation of an exciplex 3[Hg(q2-C,H,)] has been proposed on the basis of experimental and theoretical studies to account for the unusual products in the mercury-photosensitized dehydrodimerization of a series of aromatic substrates.'09 The geometries and electronic structures of the complexes formed between halide anions and cyclic trimeric perfluoro-o-phenylenemercury and some of its analogues have been modelled using the MIND0 (modified intermediate neglect of differential overlap) method.' lo Nitrogen-donor ligands Both metal centres are approximately tetrahedral in [HgL,] [Hg(CF,CO,),]* 0.7CH2CI (L = 4-benzyl-1,7-diphenyl-2,4,6-triazahepta-2,5-diene).''' The crystal structure of [HgL2][CI0,],.6CI,HCCHC12[L = 2,4,6-tris(4-pyridyl)- 1,3,5-triazene] revealed a new three-dimensional framework. '' N-Acetylpyrrole and N-phenylsul- fonylpyrrole were each selectively mercurated in the 2-position with HgC1 and the products converted to the diorganomercury derivatives with sodium iodide. These compounds transferred the ligands to ruthenium and osmium.' l3 The crystal structure of [Hg(cryptand 222)][(Hg(SCN),},] showed a polymeric array of Hg-SCN-Hg chains with each mercury also linked to two terminal SCN ligands.' l4The structures of [HgI,(dabco)] and [Hg(SCN),(dabco)] revealed HgI units linked by dabco in a chain structure with tetrahedrally co-ordinated mercury and chains of Hg(SCN) units linked by dabco in a layer structure with octahedrally co-ordinated mercury atoms."' Polymeric chains were found in the structure of [HgI,(hmta)].' " Oxygen- and sulfur-donor ligands The Crystal structure of the betaine derivative [Hg,Cl,(C,H 18N202)2]revealed a centrosymmetric 16-membered ring fused with two six-membered rings and mercury in a distorted-tetrahedra1 environment.'" The structure of two two-dimensional double-betaine complexes [(2Hg,C16(L')*Hg2C14(L')),1 and [(Hg,CI,(L2)},] Zinc Cadmium and Mercury [O,CCH(NR,)CH,CH,CH(NR,)CO,; NR = NMe L1 py L2] have been re-ported.'" Mercury@) complexes containing flexible double betaines and chloride lkands C{ Hg2(L1)C14) "1 9 C( Hg,(L2)C1 )"I and [{ Hg,(L3)Cl >"I-[-O,CCH,N+Me,(CH,),N+Me,CH,CO,-; n = 2 L1 3 L2,4 L3] have been shown to possess similar polymeric structures by X-ray diffraction."' An octahedral HgO core was found in [Hg(dmso),][CF,S0,] which may be of use as a solid-state "'Hg NMR standard.',' A series of complexes has been obtained by electrochemical oxidation of mercury in an acetonitrile solution of neutral heterocyclic thione,I2' and a new structure of Hg(SEt) has appeared.122 The structures of [2H,-et],[Hg,C1,(SCN)4] and C2H,- et],[HgBr(SCN),] revealed a packing arrangement in the chlorine compound different from that in the proton ana10gue.I~~ N,N'-Dicyclohexyldithiooxamide(H,L) upon reaction with HgX (X = C1 SCN) formed [HgCl,(H,L)] [Hg(H,L)(SCN),J and [{ HgCl,(H,L)),]*EtOH; crystal structures of the latter two compounds were ob- tained.Halogen-donor ligands The first full crystallographic characterizations of the [Hg,C1812- anion have appeared and interestingly two different structures were observed; both contained a central mercury atom with a distorted-tetrahedral geometry. However in the NEt,' salt'25 the central HgCl unit bridged through two chlorine atoms to two trigonal- planar mercury centres whereas in the [(Bu'N),Mn(p-NBu'),Mn(NHBu')(NBu')] + salt', the HgCl unit bridged through all of its chlorine atoms to two mercurycentres each with a highly distorted-tetrahedral geometry. The structure of the ditetrahedral [Hg,CI6l2 -anion has been determined in the N-phenylpipera~inium'~' and [{ Mn(NBu'),(p-NBu'),),Mn] salts.Reaction of HgI with cryptand 222 gave + [Hg(cryptand 222)][Hg,I,] the structure of which provided the first example of a discrete [Hg,I,I2- anion (Fig. 3) and can be regarded as being built up from three [HgI,] tetrahedra sharing two common edges as well as one corner common to all three tetrahedra.', The crystal structures of [R,S][HgI,] (R = Me Et)showed chains of trigonal HgI units (R = Me) or Hg,I dimers (R = Et). The triiodide predominated in melts and in solutions and this was rationalized using ab initio calculation^.'^^ The crystal structure of [Et,S],[Hg2I,]*6I, prepared from HgI and Et,SiI, revealed centrosymmetric anions linked by iodine molecules.' ,' Mercury-transition-metal complexes Reactions of [M(cp),(SnPh,)]-(M = Mo W) with HgX (X = Br I) gave [M(cp),(SnPh,)][HgX] or [M(cp),(SnPh,)],Hg depending on the reactant ratio.Treatment of [M(cp),SnPh,)]- with ZnBr or CdCl gave only the trinuclear product.13' The carbanions derived from [M(CO),(dppm)] (M = Cr Mo W) on reaction with [HgCl(R)] [R = Me Et Ph Fe(C,H,)(C,H,)] gave [M(CO),{ Ph,PCH(HgR)PPh,)].' 32 The pentanuclear complexes C{ Rh(aet),),(HgCl,),I and C( M(aet),),Hg,(NO,),I"O,l (M = co Rh) have been prepared. X-Ray crystallography showed the mercury centre to be in a highly distorted-tetrahedral ge~metry.'~ The thiolatefac-(S)-[M(aet),] (M = Co Rh) upon addition of HgO in water produced the T-cage-type octanuclear complexes [{ M(aet),),Hg,016 +;spectroscopic properties were reported.' 34 Complexes of gen- 122 I.B. GorrelI Fig. 3 Crystal structure of the [Hg3I8I2- anion (Reproduced by permission from J. Chem. SOC.,Chem. Cornmun. 1995,451) era1 formula [Pt(HgR)(H,O)(dmphen)(Z-R'02CCH=CHC02R')]BF4 (R = R' = Me; R = Me R' = Bu'; R = Bu' R' = Me) have been i~olated.'~' The structure of [Hg,Pt(CH,P(S)Ph,},]X (X = BPh, PF,) has been determined and reactivity with halogen compounds investigated. Fenske-Hall calculations showed the HOMO to be ~*(pt-S).'~~ Reaction with mercury converted the 16-electron clusters [M(Au(PPh,)},]"+ (M = Pt Pd n = 2; M = Au n = 3) into the 20-electron clusters + + [H~,M(AU(PP~,)),]~(M = Pt Pd) and [H~,Au(Au(PP~,)},]~ whereas reaction with HgZ2+ salts gave the 18-electron clusters [H~(NO,),M(AU(PP~,)}~]~ + (M = Pt Pd).'37 With Hg,I [Pt,(p-CO),(PMe,Ph),] yielded the bicapped cluster [Pt4(p- CO),(PMe,Ph),(p3-HgI)2].'38 Reaction of HgTf, AgTf dppm and Hg yielded a cluster cation based on an AgHg triangle with dppm lying along each edge.139 In thf Eu-Hg and Ph,S gave a product which crystallized from pyridine as [(~y)~Eu(p- SPh),(p3-SPh)Hg(SPh)],*2pyand which upon treatment with cadmium in pyridine yielded the cadmium analogue and with zinc in thf gave the zinc(thf) anal~gue.'~' References 1 G.-J.M. Gruter G. P. M. van Klink O.S. Akkerman and F. Bickelhaupt Chem. Rev. 1995,95 2405. 2 T. R. van den Ancker and C. L. Raston J. Organomet. 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