8 Zinc, cadmium and mercury John Malito Department of Chemistry, Cork Institute of Technology, Rossa Avenue, Bishopstown, Cork, Ireland 1 Introduction This review highlights the 1998 literature for the zinc triad. Emphasis is placed on co-ordination and organometallic chemistry. For the purposes of this review, cluster complexes are defined as those which contain at least three transition metal atoms, connected by metal–metal bonds and/or bridging ligands. 2 Co-ordination chemistry A review of some zinc-fluorophores developed since 1996 has been published,1 in which basic principles, properties and limitations are discussed with extension to real and potential biological and environmental applications. An extensive summary of solution- and solid-state chemistry for triakylsilyl-substituted dimeric phosphanides of the alkaline earth metals has included discussion of zinc compounds.2 Linear polymeric chlorocadamates(II) have been reviewed,3 and a review of solid-state 199Hg NMR spectrometry, relevant to the present review, appeared late in 1997.4 Group 15 donor ligands The X-ray crystal structure for [ZnCl 2 (quin-N 2 ] reveals a tetrahedral geometry with identical Zn–Cl bond lengths [2.241(1) and 2.244(1) Å] but significantly di§erent Zn–N bond lengths [2.050(3) and 2.074(3) Å].5 The complex, [Zn(4,4@- bipy)(H 2 O)(SO 4 )]·0.5H 2 O, exists in the solid state as a pseudo-three-dimensional co-ordination polymer,6 while the related compound, [Zn(4,4@-bipy)(H 2 O) 3 (ClO 4 )]- (ClO 4 )·(4,4@-bipy) 1.5 ·H 2 O, is composed of extended linear polymeric chains held through H-bond crosslinkages to form a two-dimensional rhombic network.7 Heating of a suspension of zinc dust in 1-methylimidazole under a carbon dioxide atmosphere a§ords [Zn(1-Me-2-Im) 2 (1-MeIm)].The crystal structure reveals bonding to the metal through both N and O atoms.8 Synthesis and detailed characterisation, including 113Cd NMR, for forty-five new Zn and Cd compounds of N-substituted Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 93–104 93imidazoles have been reported.9 The new ligand bimOH has been reported along with the X-ray crystal structure for [Zn(bimOH) 2 ][BF 4 ] 2 .10 Crystal structures have also been reported for [Zn(L)Cl](ClO 4 ) (L\a-Metpa, a-Mebqpa or a-Phtpa).11 The structure for [ZnCl 2 (4,2@-6@,4A-terpy)] shows an overall network of non-interacting chains in which the Zn atom is in a highly distorted tetrahedral environment.12 In the monomeric complex of the tetradentate (N 4 ) ligand, tris(benzimidazolylmethyl)amine, [Zn(N 4 )(PhCO 2 )](BF 4 )·MeOH, the zinc is in a close to trigonal bipyramidal environment, with the benzoate acting as a monodentate ligand.13 Structures have also been determined for the diphenylamido complexes, [MZn(NPh 2 ) 2N2 ] and [Zn(NPh 2 ) 2 - (thf) 2 ].14 In [ZnLCl 2 ], the ligand, L\phenyl 2-pyridylketoneazine 1, acts as a tridentate chelate, leading to a trigonal bipyramidal geometry.15 The crystal structure for [Zn(tepa)](ClO 4 ) 2 reveals that the zinc is tetra-co-ordinated rather than penta-co-ordinated as is observed with similar tripodal ligands, including tmpa.This is ascribed to weak co-ordination of the perchlorate ligands, but also to di§ering sizes of the ligand–metal chelate rings.16 Zinc compounds of two new tripodal N,O ligands, bis(2-pyridylmethyl)(o-hydroxybenzyl)amine and bis(2-pyridylmethyl)( 2-carboxymethyl)amine, have also been synthesised.17 X-Ray crystallography has verified that the zinc centre is penta-co-ordinated in the complex [ZnS 4 (pmdeta)] prepared from [ZnS 6 (tmeda)].This new complex reacts with elemental sulfur to produce [ZnS 5 (pmdeta)], and shows enhanced nucleophilicity in simple reactions with CS 2 , C 2 (S 2 CO) 2 and with dmad.18 Schi§-base complexes of the type [ZnL] and [Zn(HL@)2] have been prepared by reactions of [Zn(O 2 CMe) 2 ] with azomethines obtained from p-phenylenediamine and 3-methoxy-4-hydroxybenzaldehyde (H 2 L) or 3-hydroxybenzaldehyde (H 2 L@).19 A triple-helical structure, as a result of a spontaneous self-assembly process, was proposed for dinuclear Zn(II) and Cd(II) complexes of the chiragen ligand 2.20 X-Ray crystal structures have been reported for mixed Zn(II)–Cr(III) chloride complexes with urea described as [Cr(CON 2 H 4 ) 6 ][ZnCl 4 ]Cl·H 2 O and [Cr(CON 2 H 4 ) 6 ]- [ZnCl 4 ][ZnCl 3 (CON 2 H 4 )].21 Other X-ray crystal structures reported include those for [Zn(NCS) 2 (dien)] which shows trigonal bipyramidal geometry with Zn–N bond lengths in the range 1.984(7)–2.252(8)Å,22 [ZnCl 2 (N 6 C 8 H 14 )] [N 6 C 8 H 14 \3(5)- amino-5(3) methylpyrazole],23 the 4-pyridone complex [ZnCl 2 (C 5 H 5 NO) 2 ]24 and the zinc dicyanamide, [ZnMN(CN) 2N2 ].25 The structural properties of self-assembled poly[bis(quinolato)zinc] have also been investigated.26 Extensive thermal and structural studies have been carried out for some bis(pyridyl) cadmium(II) iodide complexes.27 Thermal studies have also been reported [Cd(medien)X 2 ] (X\Cl, Br, I, NCS or NO 3 )28 and the molecular structure deter- Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 93–104 942 Me Me Me Me N N N N mined for the X\NO 3 complex reveals hepta-co-ordination with the cadmium bound to three nitrogen atoms of the medien moiety and four oxygen atoms of the two bidentate nitro groups.29 The complexes [Cd(NCO) 2 L 2 (H 2 O)] 2 , [Cd(NCS) 2 L 2 ], [CdCl 2 L 2 ], [Cd(SO 4 )L 2 ]·H 2 O, and [Cd(O 2 CMe) 2 L 3 ]·H 2 O for L\3-amino-5- methylpyrazole have been synthesised and then subjected to thermal analyses.30 The crystal structure has been reported for [Cd(aepn)(NCS) 2 ].31 Mercury-199 NMR spectra and X-ray crystal structure determinations have been reported for the mercury complexes, [Hg(bmpa) 2 ](ClO 4 ) 2 and [Hg(bmpa)(NCMe)]- (ClO 4 ) 2 .These have distorted trigonal prismatic and distorted square planar structures respectively, owing to the close associations to the perchlorate moieties.32 Reactions of HgCl 2 with the potentially tetradentate ligand, tla, lead to the penta-coordinate compounds [Hg(tla)Cl 2 ] and [Hg(tla)Cl] 2 (Hg 2 Cl 6 ). In the crystal state, however, the ligand does act as a tetradentate chelate for dimer-like orientations.33 X-Ray crystallography has revealed a rutile-like three-dimensional structure for [Cd(tcm)(hmt)(H 2 O)](tcm).34 Other structures determined include the complexes, Li 4 [Hg 2 (edta) 2 ]·8H 2 O and Ba 2 [Hg 2 (teta) 2 ]·9H 2 O,35 [Me 2 NH 2 HgBr 3 ],36 and [HgCl 2 (dppf)]·MeOH for which the central mercury atom is in a tetrahedral environment. 37 Stable complexes of mercuriophosphaalkenes from the addition of organomercury halides to the Ru–P bond in [Ru(P––CH––Bu5)Cl(CA)(PPh 3 ) 2 ] (A\Oor S) have been reported with the crystal structure determined for the species shown as 3.38 P Ru Cl Cl OC PPh3 Ph3P But Hg (C5H4)Fe(C5H5) HC 3 Group 16 donor ligands As part of a continuing study of zinc carboxylates, vibrational spectra measured for anhydrous zinc acetate and zinc stearate led to the observation that stearate can also behave as a bridging bidentate ligand.39 A monomeric complex formed with 5- aminoprotic acid, [Zn(H 3 L) 2 (H 2 O) 4 ], and its related polymeric compound, Annu. Rep.Prog. Chem., Sect. A, 1999, 95, 93–104 95MZn(H 2 L)(H 2 O) 2Nn (H 4 L\5-amino-2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid), have been reported.This potentially bis(bidentate) ligand can act as both a nitrogen- and oxygen-donor ligand. Slow crystallisation from dmso solution of either the monomeric or polymeric species, however, a§ords the isolable complex [Zn(H 3 L) 2 (dmso) 2 (H 2 O) 2 ] for which the ligand bonds to the metal through one carboxylate oxygen atom exclusively.40 Each of the four ligands in the distorted tetrahedral complex, [Zn(dips) 2 (dmso) 2 ], acts in a monodentate fashion binding to the metal centre through an oxygen atom.This complex proves to be more e§ective than the free dips ligand as an anti-convulsant and/or inhibitor of seizures.41 Syntheses, spectral studies and structural characterisations have been reported for [ZnL 2 (MeIm) 2 ] (L\2-quinolinecarboxylate),42 and the first zinc(II) ferrocenedicarboxylate, [Zn(1,1@-ferdc)(MeIm) 2 ] 2 .43 Some new metal chelated species, including those of zinc, with salicyladoxime (salo) have been synthesised and characterised by absorption spectroscopy.The salo ligand is bidentate, bonding through both the phenolic oxygen and the oxime nitrogen atoms.44 Crystal structures have been determined for the aryloxide compounds, Na[Zn(OC 6 H 3 Ph 2 -2,6) 3 (H 2 O)] and Na[Zn 2 (OC 6 H 3 Pr* 2 -2,6) 4 Cl]·3thf.45 Solution and solid-state structural studies have been reported for phosphine adducts of monomeric zinc bis(phenoxides) of the type, ZnQ 2 L (HQ\2,6-di-tert-butylphenol; L\PMePh 2 , PCy 3 ).46 The synthesis and structure have been reported for pseudo-octahedral Na 2 [Zn(ida) 2 ]·7H 2 Oand pseudobicapped octahedral Na 4 [Hg(nta) 2 ]·7H 2 O complexes.47 The dimeric dithiolate complex, [MZn(bme-daco)N2 ], and its cadmium analogue have been studied as models for the active site of zinc-dependent methylation proteins. 48 The new ligand, 2,6-(Ph 2 PCH 2 CH 2 SCH 2 ) 2 C 5 H 3 N, has been prepared and the complexes [ML(O 3 SCF 3 ) 2 ] (M\Zn or Cd) obtained.Details of the X-ray crystal structure have been given for the CD species which shows an unusual distorted pentagonal-bipyramidal geometry, in which the cadmium centre bonds to all five donor atoms of the ligand as well as to oxygen atoms of the two monodentate CF 3 SO 3 ~ anions.49 The thiolate complexes, (Me 4 N) 2 [M 4 (o-SC 6 H 4 Me) 10 ] (M\Zn or Cd), have been synthesised, characterised by various methods, and observed to have selectively scavenging e§ects on hydroxyl radicals.50 Zinc thiolate compounds of the type [Zn(bima)(SR)][X] (R\Ph or CH 2 Ph; X\BPh 4 or ClO 4 ), have also been prepared.X-Ray crystallography shows that the zinc centre is in a pseudo-tetrahedral environment.51 Some novel dimeric carbamato species of cadmium, [CdL 2 (O 2 CNEt 2 )] 2 [L\Me 2 N(CH 2 ) 2 NMe 2 , py or (MeNCH 2 ) 3 ] as well as the monomeric complex [Cd(O 2 CNEt 2 ) 2 ] have been reported.52 A family of monomeric cadmium(II) bis(phenoxides) of general formula, [Cd(OC 6 H 3 R 2 -2,6) 2 ](base) 2–3 (R\Ph, Bu5 or Me; base\thf, tht, py or propylene carbonate), have been synthesised.Their reactivities with the small molecules CO 2 , COS and CS 2 have been studied.No reaction was observed with carbon dioxide but the others do undergo insertion reactions. It was found that the parent compounds show reduced activity for the copolymerisation of CO 2 with epoxides, a reaction for which the analogous zinc(II) bis(phenoxides) are highly active.53 The X-ray crystal structure for [CdCl 2 (imt) 2 ] has been re-determined.The Cd–S bonds [2.525(2) and 2.535(2)Å] are appreciably longer than those measured for the analogous gold(I) and copper(II) complexes while the intraligand C–S bonds are the Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 93–104 96same.54 Crystal structures have also been reported for the bis(thiourea) cadmium halide complexes, [CdX 2MSC(NH 2 ) 2N2 ] (X\Cl, Br or I).These pseudo-tetrahedral complexes are isostructural although the iodide complex crystallises in a di§erent space group.55 Thiosulfate acts as a polydentate ligand in the complex, [Cd(S 2 O 3 )(phen)(H 2 O)]·H 2 O, for which the crystal structure reveals a polymeric chain structure with each cadmium atom sitting in a distorted octahedral environment. 56 The complexes [CdHL(pn) 2 ]`and [CdL(pn) 2 ] for H 2 L\2-thiouracil or 6-methyl-2-thiouracil have been reported.57 Polytopal isomerism of the thiobenzoate complex (PPh 4 )[CdMS(O)CPhN3 ] has been revealed by an X-ray crystallographic study.58 The X-ray crystal structure has also been reported for the analogous triethylammonium salt.59 Multinuclear NMR (13C, 113Cd and 199Hg) and X-ray crystallographic studies for the related species (Ph 4 As) 2 [MCl 4 HgMS(O)CPhN2 ] (M\Cd or Hg), formed from Ph 4 AsCl·H 2 O, [HgMS(O)CPhN2 ] and MCl 2 (M\Cd or Hg), have also been reported.60 The complex [CdMCy 2 P(Se)C(S)NPhN2 ] has been synthesised and characterised by X-ray crystallography which shows the CdSe 2 S 2 core to be in a tetrahedral arrangement. 61 The selenato complexes, containing a chelating oxazoline ligand, [MMSe(ox@)N2 ] (M\Zn, Cd or Hg) each have a helical structure in the solid state that is maintained in solution.62 Solid- and solution-state 113Cd and 77Se NMR spectra have been reported for complexes of the general formula, [Cd(SeR) 2 L 2 ] (L\N-donor ligand), and the X-ray crystal structure was determined for the complex, [Cd(SeC 6 H 2 Pr* 3 -2,4,6) 2 (bipy)].These complexes serve as models for biologically occurring species of general formula, [M(S-Cys) 2 (His) 2 ].63 Another study found that cysteine and histidine both behave as bidentate ligands with Zn.64 Addition of E–– C––NR (E\S, R\Bu5; E\Se, R\Cy) to [CdMN(SiMe 3 ) 2N2 ] in the presence of tetramethylethylenediamine yields [Cd(ESiMe 3 )] or (tmeda)[CdMN(SiMe 3 ) 2N(SiSiMe 3 )]n.Upon protolysis, the latter complex yields MCd[XR](SiSiMe 3 )Nn (X\Oor S, R\SiPh 3 ; X\O, R\2,6-di-tert-butyl-4-methylphenyl). 65 Lewis acid adduct formation of [PhHgS(S)POGO] [G\–CH 2 CH(Me)–, –(CH 2 ) 5 – or –CMe 2 CMe 2 –) with mercury(II), cadmium(II) and silver(I) salts gave 24 bimetallic derivatives, generally formed through co-ordination of the thiono sulfur to the soft metal centre.66 The thioethereal complexes, [HgMN(CH 2 CH 2 SCHMe 2 ) 3N] 2 - [Hg 2 X 6 ] (X\Cl, Br) were prepared directly by reaction of the appropriate mercuric halide with ligand.The crystal structure is reported for the chloro-species.67 X-Ray crystallography shows [Hg(dmit)(phosphine)] (phosphine\dppe, dppf) to be a onedimensional co-ordination polymer held together by bridging diphosphine ligands.This structure is ascribed to the marked preference of the Hg to be in a tetrahedral configuration.68 The synthesis and structure for the first heavy metal complex of an x-thiocaprolactam, [HgCl 2 (C 6 H 11 NS-S) 2 ] 4 (C 6 H 11 NS\1-azacycloheptane-2-thione), has been reported. Bonding distances are 2.480(2) and 2.613(2)Å for Hg–Cl, and 2.496(2)Å for Hg–S.69 The dimeric complexes, [MHg(C 5 H 4 S 5 )X 2N2 ] (X\Cl or Br) for C 5 H 4 S 5 \4,5-ethylenedithio-1,3-dithiole-2-thione, have been characterised, including an X-ray structure determination for the chloro species.70 The crystal structure, with corroborating spectroscopic data, has been reported for a mercury dimer, [MHgCl 2 LN2 ] 5 formed from HgCl 2 and benzothiazole. The resulting 2-aminoben- Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 93–104 97N N S Hg Cl S Cl H H 4 zenethiol ligand (L) exists in the zwitterionic form. Significant bond distances include Hg–Cl 2.383(1), Hg–S 2.340(2), Hg–l-Cl 2.720(1) and 2.976(1)Å.71 +NH3 S Hg Cl – Cl – Cl Hg Cl S +NH3 5 Halide and pseudo-halide donor ligands A novel blue luminescent complex, [Zn(Hdpa)(CN) 2 ], shows potential as a material for blue-light emitting diodes.Self-assembly is observed for this compound in the crystal state via intermolecular hydrogen bonding [N–H· · ·NC 2.965(7)Å], and faceto- face p–p aromatic stacking to form two-dimensional sheets.72 A detailed lowtemperature multinuclear (13C, 15N, 113Cd)NMRstudy of the complexing of divalent zinc and cadmium with isothiocyanates in solution has been reported.73 Formation of the layered co-ordination polymer, (4-cyanopyridine)cadmium iodide diiodine is assisted by two types of iodide bonding, involving co-ordinated iodine atoms of the layers and iodine molecules that bridge adjacent layers.74 The use of methyl acetate as the guest molecule has provided a novel mineralomimetic Cd(CN) 2 framework, and the novel clathrate species, [Cd(CN) 2 ]·MeCO 2 Me.The X-ray structure was reported for the latter material.75 Solid state NMR studies have been reported for the series, [Hg(X)(O 2 CMe)] (X\Cl, Br, I, CN or SCN), and the X-ray crystal structure of the cyano species has been determined.76 The 199Hg MAS NMR spectra were also measured for [Hg(SCN) 2 ], [Hg(SeCN) 2 ], M[Hg(SCN) 3 ], M 2 [Hg(SCN) 4 ] (M\K or Cs) and K 2 [Hg 3 (NCO) 8 ], along with the crystal structure for the selenocyanato species.77 In the course of an investigation, employing Raman spectroscopy and factor analysis, into the equilibria displayed by Hg(SCN) 2 /NaSCN in dmf solution, the following species were tentatively assigned, [Hg(SCN)]`, [Hg(SCN) 2 ], [Hg(SCN) 3 ]~ and [Hg(SCN) 4 ]2~.78 Other ligands Phase transition studies by the DSC method for crystalline [M(H 2 O) 6 ][ClO 4 ] 2 Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 93–104 98(M\Zn, Cd or Hg) have been reported.79 The complex [Zn 2 L 2 (OH) 2 ] for L\N- [(benzoylamino)thioxomethyl]glycine proves to be an e§ective anti-oxidant because it demonstrates scavenging e§ects on dioxygen radicals.80 The synthesis, 11B NMR spectra and X-ray crystal structure have been reported for [NBu/ 4 ] 2 [Cd(g3-B 6 H 6 ) 2 ]· 2CH 2 Cl 2 .81 The amine-carboxylate adduct, bis(morpholine borane carboxylate)zinc(II) dihydrate has been shown to have antitumor activity.82 Insertion of CO 2 into one the B–H bonds of the bis(pyrazolyl)hydroborato ligand in [ZnCl(HBp5.B6,*.P3)] yields the complex, [ZnClMg3-(HCO 2 )Bp5.B6,*.P3N]ZnCl, characterised by single crystal X-ray di§raction.83 The trigonal fragment, [Au(dpnapy) 3 ]`, acts as a metalloligand with a strong a¶nity for Cd(II) in [AuCd(dpnapy) 3 ][ClO 4 ] 3 .84 The synthesis and X-ray crystal structure of the fulleride, [Cd(NH 3 ) 6 ]C 60 ·6NH 3 , have been reported.85 3 Macrocyclic compounds The structure for [ZnCl(Me 3 [12]aneN 3 )](PF 6 ) has been assessed as a model for zinc-containing active sites on hydrolytic metalloenzymes such as carbonic anhydrase.The parent ligand, [12]aneN 3 , has previously been found to be an appropriate ligand for this purpose.86 Crystal structures have been reported for [ZnCl([15]aneN 4 )] (ClO 4 )87 and for the zinc complex of the new ligand, 5,10,15,20-tetra[4(n-butylphenyl) ethynyl]porphyrin.88 Both 1D and 2D 1H NMR were used to study the dinuclear complex [Zn(TTP-m-O(CH 2 ))] 2 (CH 2 ).In solution, this compound axially co-ordinates both pyrazine and pyrimidine. The crystal structure for the former species shows a 1:1 adduct formation but with the pyrazine acting as a bridging ligand.89 A zinc porphyrin bound to fullerene has shown some interesting luminescence and photophysical properties,90 and the opto-electronic properties for several other conjugated porphyrin oligomers have also been studied.91 The preparation and X-ray crystal structure have been reported for a unique 2: 1 complex of mercuric chloride with 5-oxa-2,8-dithiabicyclo[7.4.1]tetradeca-9,11,13- trien-14-one.92 Cadmium and mercury complexes of the semi-rigid diimine ligand, OpyNpy 2 6, were prepared from a [1]2] Schi§ base condensation of 2,6-bis(2- aminophenoxymethyl)pyridine and 2-pyridinecarbaldehyde in the presence of MX 2 (M\Cd or Hg; X\NO 3 or ClO 4 ). X-Ray di§raction revealed a mono-helical structure for the Cd complex, [Cd(OpyNpy 2 )](NO 3 ) 2 ·2H 2 O.93 4 Cluster chemistry The crystal structure has been reported for [Zn 3 (bdc) 3 ]·6MeOH,94 and the cluster [Zn 8 L 4 (OH) 2 ](ClO 4 ) [H3 L\1,3-bis(salicylamino)propan-2-ol] which has been shown to have a unique cage structure composed of eight zinc atoms, four alkoxo O atoms and eight ligand phenoxoObridges.95 The synthesis and molecular structure of a new type of zinc sulfide cluster, [Zn 10 S 7 (py) 9 (SO 4 ) 3 ]·3H 2 O, has been reported,96 and also for the zinc selenide and telluride clusters, [NEt 4 ] 2 [ZnCl 4 (SePh) 6 ], [NEt 4 ] 2 - [Zn 8 Cl 4 Se(SePh) 12 ], [Zn 8 Se(SePh) 14 (PPr/ 3 ) 2 ], [HPPr/ 2 R] 2 [Zn 8 Cl 4 Te(TePh) 12 ] (R\Pr/ or Ph), and [Zn 10 Te 4 (TePh) 12 (PR 3 ) 4 ] (R\Pr/ or Ph).97 Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 93–104 996 N N N O O N N In the solid state, [Cd 7 (tren) 12 ][ClO 4 ] 14 is made up of flat star-shaped disks composed of Cd(tren) moieties linked by other tren ligands.98 Other crystal structure determinations have included those for [Cd 3 (py) 8 (O 2 CMe) 4 ](ClO 4 ) 2 ,99 [Cd 10 Se 4 (SePh) 12 (PPh 3 ) 4 ] and [Cd 16 (SePh) 32 (PPh 3 ) 2 ],100 and the tri-heteropolymetallic species, [(dppf)Pt(l-L) 2 CdX 2 ] (X\Cl, Br or I) and [M(dppf)Pt(l- L) 2N2 Cd][X] 2 (X\BF 4 or ClO 4 ) for HL\Hpz, Hdmpz or Mepz.101 The crystal structure for [Hg 3 (H 2 pdm) 2 (Hpdm)(l-Cl) 2 Cl 3 ] shows that the metal environment is pseudo-octahedral for the central Hg atom but distorted squarepyramidal for the two end Hg atoms.102 Synthesis and crystal structures have been reported for [Hg 6 (SePh) 12 (PBu5 3 ) 2 ] and (HPBu5 3 ) 2 [Hg 6 (SePh) 14 ],103 the three new Hg–Fe cluster complexes: [Hg 7MFe(CO) 4N5 (SBu5) 3 Cl], [Hg 14 Fe 12MFe(CO) 4N6 - S 6 (SBu5) 8 Br 18 ] and [Hg 39 Fe 8MFe(CO) 4N18 S 8 (SBu5) 14 Br 28 ],104 as well as for several related phosphinido-and phosphinidene-bridged cluster complexes: [Hg 3MFe(CO) 4N2 - X 2 ] (X\Cl, Br), [Hg 10MFe(CO) 4N4 (PBu5) 4 Cl 4 ], [Hg 14MFe(CO) 4N5 (PBu5) 8 Cl 2 ], [SiMe 3 OPPr* 3 ][Hg 12MFe(CO) 4N7 (PBu5) 4 (PBu5SiMe 3 )Br 2 ], [Hg 5MFe(CO) 4N3 (PBu5) 2 - Br 2 ], [Hg 8MFe(CO) 4N4 (P 2 Ph 2 ) 2 (PPr/ 3 )Cl 4 ], [Hg 8MFe(CO) 4N4 (P 2 Ph 2 ) 2 (PEtPh 2 )Cl 4 ], and [Hg 10MFe(CO) 4N6 (P 2 Ph 2 ) 2 (PPr/ 3 )Br 4 ].105 The synthesis of the first polymetallic mesocycle containing the first example of an attractive Hg–Cu interaction has been reported, and the molecular structure 7 for this compound has been determined by X-ray crystallography.The observed Cu–Hg separation of 2.689(2)Å is only slightly longer than the sum of the Pauling covalent radii (2.61Å).106 5 Organometallic chemistry IR and Raman spectroscopic studies for both solution and solid-state samples indicate that in solution zincocene has the slip-sandwich structure, [Zn(g5-C 5 H 5 )(g1-C 5 - H 5 )].107 The synthesis and the crystal structure determination have been reported for [Zn(C 6 F 5 ) 2 ].108 The homoleptic organometallic species [MMRN2 ] or [MR 2 ] (M\Zn, Cd or Hg) have been prepared for a series of ligands derived from LiC 6 H 4 (CH 2 NEt 2 )-2, LiC 6 H 3 (CH 2 NMe 2 )-2,6, LiC 6 H 3 (CH 2 NEt 2 ) 2 -2,6, Li(CH 2 ) 3 NC 5 H 10 and [Li(CH 2 ) 3 ] 2 NMe.Whether the dimer or monomer forms depends upon the nature of R.109 The X-ray crystal structure was determined for [Li(tmeda) 2 ][Zn(C 6 H 2 Pr* 3 -2,4,6)].110 Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 93–104 100A boron–zinc transmetallation methodology has been employed to prepare [ZnCH 2 CHRCH 2 ZnCH 2 CHRCH 2 ] and [Zn(CH 2 ) 3 Hg(CH 2 ) 3 ] (R\H or Bu).Based on NMR spectra, the structures have been assigned as eight-membered rings. Under appropriate conditions these species are reactive with electrophiles such as allyl bromides or propargyl bromide and benzoyl chloride.111 The compound [(Z)- PhCH 2 CH 2 CH––CMeHgBr], prepared from the Grignard reaction of (Z)-2-bromo-5- phenylpent-2-ene with HgBr 2 in thf,112 reacts with silver acetate in thf to give [(Z)- PhCH 2 CH––CMeHg(O 2 CMe)]113 or can undergo an SnCl 2 -mediated coupling in the presence of NaOH in either ethanol or water to give [(PhCH 2 CH 2 CH––CMe) 2 Hg].114 The bifunctional ligand Hdpb and its oxide, dpbo, react with mercury to form [HgMe(L)] (L\dpb or dpbo).The X-ray crystal structures have been reported.115 Organometallic pyrimidine derivatives of the type [RHgL] (R\o-, p-HOC 6 H 4 ; L\uracil or thymine) have been synthesised.116 The cationic species [HgR]` (R\Me, Et, Pr, Pr*, Ph, C 6 H 4 Me-p, CH 2 Ph, 5-methylthienyl or ferrocenyl) have been reacted to form complexes with hydridotris(3,5-diphenyl-1H-pyrazol-1-yl)borato and hydridotris(4-bromo-1H-pyrazol-1-yl)borato ligands.The former appears to be the better donor ligand.117 Reactions of [Hg(O 2 CR) 2 ] (R\Et, Pr, Pr* or Bu) with methylphenylacetylene in appropriate acidic solvents yield mixtures of cis and trans 8 Me O O O O O Hg Br Annu.Rep. Prog. Chem., Sect. A, 1999, 95, 93–104 101adducts of the type, [RC(O)CP––CMeHgCl].118 Syntheses and reactions of HgCl 2 , HgO and Hg(O 2 CCF 3 ) 2 with the fluorophenyl ligands, C 6 H 4 F-2, C 6 H 3 F 2 -2,6, and C 6 H 2 F 3 -2,4,6, have been reported along with some analogous chemistry for cadmium starting materials.119 The reaction of HgCl 2 with LiC 5 Me 4 SiMe 2 CMe 3 (\LiCp4) yields [Hg(g1-Cp4) 2 ] and the novel tetramer, [Hg(g1-Cp4)Cl] 4 .The crystal structures for these compounds were reported, and an NMR study (13C and 199Hg) indicated that neither compound is fluxional.120 The organometallic compound, 1-bromomercurio- 2-(2,5,8,11,14-pentaoxapentadecyl)benzene, [HgBr(C 16 H 25 O 5 )], has a nearly linear geometry at the Hg atom, and its structure in the solid state is best described as an open-chain polyether complex 8.121 References 1 E.Kimura and T. Koike, Chem. Soc. Rev., 1998, 27, 179. 2 M. Westerhausen, B. Rademacher, M.Hartmann, M. Wieneke and M. Digeser, in Organosilicon Chem. III (Muench Silicontage), ed. A. Norbet and J. Weis, Wiley-VCH Verlag GmbH, Weinheim, Germay, 3rd edn., 1996 (pub. 1998), p. 157; Chem. Abstr., 1998, 128, 238391a. 3 A.B. Corradi, A.M. Ferrari and C. C. Pellacani, Inorg. Chim. Acta, 1998, 272, 252. 4 G.A. Bowmaker, R. K. Harris and S.-W. Oh, Coord. Chem. Rev., 1997, 167, 49. 5 Y. Cui, D. Long, W. Chen and J. Huang, Acta Crystallogr., Sect. C, 1998, 54, 1605. 6 S.D. Huang, R.-G. Xiong and P. H. Sotero, J. Solid State Chem., 1998, 138, 361. 7 M.-L. Tong, J.-W. Cai, X.-L. Yu, X.-M. Chen, S. W. Ng and T. C. W. Mak, Aust. J. Chem., 1998, 51, 637. 8 T.A. Zevaco, R. Trotzki, H. Go� rls and E. Dinjus, Inorg. Chem. Commun., 1998, 1, 30. 9 C. Pettinari, F.Marchetti, A. Cingolani, S. I. Troyanov and A. Drozdov, Polyhedron, 1998, 17, 1677. 10 R. Bhalla, M. Helliwell, R. L. Beddoes, D. Collison and C. D. Garner, Inorg. Chim. Acta, 1998, 273, 225. 11 J. W. Canary, C. S. Allen, J. M. Castagnetto, Y.-H. Chiu, P. J. Toscano and Y. Wang. Inorg. Chem., 1998, 37, 6255. 12 M. Barqu� in, J. Cancela, M.J. Gonza� lez Garmendia, J. Quintanilla and U.Amador, Polyhedron, 1998, 17, 2373. 13 D. E. Fenton, H. Adams and Q.-Y. He, Acta Crystallogr., Sect. C, 1998, 54, 286. 14 M.A. Putzer, A. Dashti-Mommertz, B. Neumueller and K. Dehnicke, Z. Anorg. Allg. Chem., 1998, 624, 263. 15 E. Amadei, M. Carcelli, S. Ianelli, P. Cozzini, P. Pelagatti and C. Pelizzi, J. Chem. Soc., Dalton Trans., 1998, 1025. 16 X. Xu, C. S. Allen, C.-L. Chuang and J.W. Canary, Acta Crystallogr., Sect. C, 1998, 54, 600. 17 A. Troesch and H. Vahrenkamp, Eur. J. Inorg. Chem., 1998, 827. 18 R. J. Pa§ord and T. B. Rauchfuss, Inorg. Chem., 1998, 37, 1974. 19 S. A. Kuznetsova, A. V. Bicherov, N. I. Dorokhova, L. I. Kuznetsova, E. G. Amarskii, B. N. Kuznetsov, A. S. Burlov and A. D. Garnovskii, Russ. J. Coord. Chem., 1998, 24, 43. 20 H.Murner, A. von Zelewsky and G. Hopfgartner, Inorg. Chim. Acta, 1998, 271, 36. 21 N. G. Furmanova, V. B. Bergo, V. F. Resnyanskii, K. S. Sulaimankulov, Sh. Zh. Zhorobekova and D. K. Sulaimankulova, Kristallografiya, 1998, 43, 646. 22 T.-H. Lu, J.-M. Lo, B.-H. Chen, M.-Y. Yeh, S.-F. Tung, W.-T. Huang and H.-H. Yao, Acta Crystallogr., Sect. C, 1998, 54, 1067. 23 Z. K. Jacimovic, B. V.Prelesnik, G. A. Bogdanovic, E. Z. Iveges and V. M. Leovac, Z. Kristallogr. – New Cryst. Struct., 1998, 213, 35. 24 R. Masse and Y. Le Fur, Z. Kristallogr. – New Cryst. Struct., 1998, 213, 114. 25 J. L. Manson, D.W. Lee, A. L. Rheingold and J. S. Miller, Inorg. Chem., 1998, 37, 5966. 26 D. L. Thomsen III, T. Phely-Bobin and F. Papadimitrakopoulos, Mater. Res. Soc. Symp. Proc., 1998, 488, 759. 27 R. D. Bailey, L. L. Hook, A. K. Powers, T. W. Hanks and W.T. Pennington, Cryst. Eng., 1998, 1, 51; Chem. Abstr., 1998, 129, 117053t. 28 A. Mondal, S. Chaudhuri, A. Ghosh, I. R. Laskar and N. R. Chaudhuri, Acta Chem. Scand., 1998, 52, 1202. 29 A. Mondal, S. Chaudhuri, A. Ghosh, I. R. Laskar and N. R. Chaudhuri, Acta Chem. Scand., 1998, 52, 1064. 30 S. K. Meszaros, E. Z.Iveges, V. M. Leovac, Lj. S. Vojinovic, A. Kovacs, G. Pokol, J. Madarasz and Z. K. Jacimovic, Thermochim. Acta, 1998, 316, 79. 31 A. Mondal, G. Mostafa, A. Ghosh and N. R. Chaudhuri, J. Chem. Res., 1998, (S) 570. 32 D. C. Bebout, A. E. DeLanoy, D. E. Ehmann, M. E. Kastner, D. A. Parrish and R. J. Butcher, Inorg. Chem., 1998, 37, 2952. Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 93–104 10233 D.C. Bebout, J. F. Bush II, K. K. Crahan, M. E. Kastner and D. A. Parrish, Inorg. Chem., 1998, 37, 4641. 34 S. R. Batten, B. F. Hoskins and R. Robson, Inorg. Chem., 1998, 37, 3432. 35 A. Albinati, V. Gramlich, G. Anderegg, F. Lianza, W. Petter and H. Bommeli, Inorg. Chim. Acta, 1998, 274, 219. 36 H. Terao, M. Hashimoto, T. Okuda and A. Weiss, Z. Naturforsch., Teil A, 1998, 53, 559. 37 J. McGinley, V. McKee and C. J. McKenzie, Acta Crystallogr., Sect. C, 1998, 54, 345. 38 A. F. Hill, C. Jones, A. J. P. White, D. J. Williams and J. D. E. T. Wilton-Ely, J. Chem. Soc., Dalton Trans., 1998, 1419. 39 T. Ishioka, Y. Shibata, M. Takahashi and I. Kanesaka, Spectrochim. Acta, Part A, 1998, 54, 1811. 40 N. Lalioti, C. P. Raptopoulou, A. Terzis, A. Panagiotopoulos, S.P. Perlepes and E. Manessi-Zoupa, J. Chem. Soc., Dalton Trans., 1998, 1327. 41 G. Morgant, B. Viossat, J.-C. Daran, M. Roch-Arveiller, J.-P. Giroud, N.-H. Dung and R. J. Sorenson, J. Inorg. Biochem., 1998, 70, 137. 42 T. A. Zevaco, H. Go� rls and E. Dinjus, Inorg. Chim. Acta, 1998, 269, 283. 43 T. A. Zevaco, H. Go� rls and E. Dinjus, Polyhedron, 1998, 17, 613. 44 V. Ramesh, P.Umasundari and K. K. Das, Spectrochim. Acta, Part A, 1998, 52, 285. 45 D. J. Darensbourg, J. C. Yoder, G. E. Struck, M.W. Holtcamp, J. D. Draper and J. H. Reibenspies, Inorg. Chim. Acta, 1998, 274, 115. 46 D. J. Darensbourg, M. S. Zimmer, P. Rainey and D. L. Larkins, Inorg. Chem., 1998, 37, 2852. 47 J. Wang, W.-Q. Zhang, X.-D. Zhang, Y. Xing, Y.-H. Lin and H.-Q. Jia, Gaodeng Xuexiao Huaxue Xuebao, 1998, 19, 517; Chem.Abstr., 1998, 129, 22524h. 48 C. A. Grapperhaus, T. Tuntulani, J. H. Reibenspies and M. Y. Darensbourg, Inorg. Chem., 1998, 37, 4052. 49 S.-M. Kuang, Z.-Z. Zhang and T. C.W. Mak, J. Chem. Soc., Dalton Trans., 1998, 317. 50 S. Guo, E. Ding, S. Liu and Y. Yin, J. Inorg. Biochem., 1998, 70, 7. 51 R. Burth and H. Vahrenkamp, Z. Anorg. Allg.Chem., 1998, 624, 381. 52 M.A. Malik and P. O’Brien, Inorg. Chim. Acta, 1998, 274, 239. 53 J. Darensbourg, S. A. Niezgoda, J. D. Draper and J. H. Reibenspies, J. Am. Chem. Soc., 1998, 120, 4690. 54 A. R. Al-Arfaj, J. H. Reibenspies, A. A. Isab and M. Sakhawat Hussain, Acta Crystallogr., Sect. C, 1998, 54, 51. 55 C. Marcos, J. M. Alia, V. Adovasio, M. Prieto and S. Garcia-Granda, Acta Crystallogr., Sect. C, 1998, 54, 1225. 56 S. Baggio, R. Baggio and M. T. Garland, Acta Crystallogr., Sect. C, 1998, 54, 1099. 57 A. R. Sarkar and M. Sarkar, Synth. React. Inorg. Met.-Org. Chem., 1998, 28, 51. 58 P. A. W. Dean, J. J. Vittal, D. C. Craig and M. L. Scudder, Inorg. Chem., 1998, 37, 1661. 59 J. J. Vittal and P. A. W. Dean, Acta Crystallogr., Sect. C, 1998, 54, 319. 60 J.J. Vittal and P. A. W. Dean, Polyhedron, 1998, 17, 1937. 61 R. Kramolowsky, J. Sawluk, G. Siasios and E. R. T. Tiekink, Inorg. Chim. Acta, 1998, 269, 317. 62 G. Mugesh, H. B. Singh, R. P. Patel and R. J. Butcher, Inorg. Chem., 1998, 37, 2663. 63 R. Subramanian, N. Govindaswamy, R. A. Santos, S. A. Koch and G. S. Harbison, Inorg. Chem., 1998, 37, 4929. 64 P. R. Rabindra, A. M. Reddy and M.Radhika, Indian J. Chem., Sect. A, 1998, 37, 775. 65 J. R. Babcock, R. W. Zehner and L. R. Sita, Chem. Mater., 1998, 10, 2027. 66 S. K. Srivastava, S. Jain and S. B. Saxena, Synth. React. Inorg. Met.-Org. Chem., 1998, 28, 1431. 67 F. Cecconi, C. A. Ghilardi, S. Midollini and A. Orlandini, Inorg. Chim. Acta, 1998, 269, 274. 68 T. R. Jensen, J. McGinley, V. McKee and C. J.McKenzie, Acta Chem. Scand., 1998, 52, 622. 6ez Gaytan, S. Bernes, E. R. de San Miguel Guerrero, J. P. Bernal and J. De Gyves, Acta Crystallogr., Sect. C, 1998, 54, 49. 70 J. Dai, M. Munakata, G.-Q. Bian, Q.-F. Xu, T. Kuroda-Sowa and M. Maekawa, Polyhedron, 1998, 17, 2267. 71 N. Davidovic, D. Matkovic-Calogovic, Z. Popovic and I. Vedrina-Dragojevic, Acta Crystallogr., Sect.C, 1998, 54, 574. 72 K.-Y. Ho, W.-Y. Yu, K.-K. Cheung and C.-M. Che, Chem. Commun., 1998, 2101. 73 A. Fratiello, V. Kubo-Anderson, D. J. Lee, T. Mao, K. Ng, S. Nickolaisen, R. D. Parrigan, V. San Lucas, W. Tikkanen, A. Wong and K. Wong, J. Solution Chem., 1998, 27, 331. 74 R. D. Bailey and W.T. Pennington, Chem. Commun., 1998, 1181. 75 T. Kitazawa, J. Mater. Chem., 1998, 8, 671. 76 G. A. Bowmaker, A. V. Churakov, R. K. Harris and S.-W. Oh, J. Organomet. Chem., 1998, 550, 89. 77 G. A. Bowmaker, A. V. Churakov, R. K. Harris, J. A. K. Howard and D. C. Apperley, Inorg. Chem., 1998, 37, 1734. 78 S. Sasic, A. Antic-Jovanovic and M. Jeremic, J. Chem. Soc., Faraday Trans., 1998, 94, 3255. 79 A. Migdal-Mikuli, E. Mikuli and J. Mayer, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect.C, 1998, 9, 205. 80 M. Junfeng, W. Jigui, W. Liufang, R. Yanping and Z. Yingnian, Synth. Inorg. Met.-Org. Chem., 1998, 28, 917. 81 T. Schaper and W. Preetz, Inorg. Chem., 1998, 37, 363. 82 M.C. Miller III, A. Sood, B. F. Spielvogel and I. H. Hall, Appl. Organomet. Chem., 1998, 12, 87. 83 P. Ghosh and G. Parkin, J. Chem. Soc., Dalton Trans., 1998, 2281. Annu. Rep. Prog.Chem., Sect. A, 1999, 95, 93–104 10384 W.-H. Chan, K.-K. Cheung, T. C. W. Mak and C.-M. Che, J. Chem. Soc., Dalton Trans., 1998, 873. 85 K. Himmel and M. Jansen, Eur. J. Inorg. Chem., 1998, 1183. 86 N.W. Alcock, H. J. Clase, S. Siltchenko, E. Rybak-Akimova and D. H. Busch, Acta Crystallogr., Sect. C, 1998, 54, 338. 87 K. Panneerselvam, T.-H. Lu, T. Y. Chi, C. Pariya, F.-L.Liao and C.-S. Chung, Acta Crystallogr., Sect. C, 1998, 54, 712. 88 H. L. Anderson, A. P. Wylie and K. Prout, J. Chem. Soc., Perkin Trans. 1, 1998, 1607. 89 S. Wolowiec, Polyhedron, 1998, 17, 1295. 90 E. Dietel, A. Hirsch, E. Eichhorn, A. Rieker, S. Hackbarth and B. Ro� der, Chem. Commun., 1998, 1981. 91 P. N. Taylor, J. Huuskonen, R. T. Aplin, G. Rumbles, E. Williams and H. L. Anderson, Chem.Commun., 1998, 909. 92 A. Mori, K. Kubo, N. Kato, H. Takeshita, M. Shiono and N. Achiwa, Heterocycles, 1998, 47, 149. 93 N. Beynek, M. McPartlin, B. P. Murphy and I. J. Scowen, Polyhedron, 1998, 17, 2137. 94 H. Li, C. E. Davis, T. L. Groy, D. G. Kelley and O.M. Yaghi, J. Am. Chem. Soc., 1998, 120, 2186. 95 M. Mikuriya N. Tsuru, S. Ikemi and S. Ikenoue, Chem. Lett., 1998, 879. 96 B. Ali, I. G. Dance, D. C. Craig and M.L. Scudder, J. Chem. Soc., Dalton Trans., 1998, 1661. 97 A. Eichhoefer, D. Fenske, H. Pfistner and M. Wunder, Z. Anorg. Allg. Chem., 1998, 624, 1909. 98 P. Klufers and P. Mayer, Acta Crystallogr., Sect. C, 1998, 54, 722. 99 W.-X. Zhang, C.-Q. Ma, J. Li, X.-N. Wang, Z.-G. Yu and D.-H. Jiang, Jiegou Huaxue, 1998, 17, 57; Chem. Abstr., 1998, 128, 18675r. 100 S. Behrens, M. Bettenhausen, A. Eichho� fer and D. Fenske, Angew. Chem., Int. Ed. Engl., 1997 (pub. 1998) 36, 2797. 101 C. Pettinari, F. Marchetti, A. Cingolini, S. I. Tryanov and A. Drozdov, J. Chem. Soc., Dalton Trans., 1998, 3335. 102 N. Farfan and H. Hopfl, Heteroat. Chem., 1998, 9, 377. 103 M. Bettenhausen and D. Fenske, Z. Anorg. Allg. Chem., 1998, 624, 1245. 104 D. Fenske and M. Bettenhausen, Angew. Chem., Int. Ed., 1998, 37, 1291. 105 J. Eisenmann, D. Fenske and F. Hezel. Z. Anorg. Allg. Chem., 1998, 624, 1095. 106 M. Be� nard, U. Bodensieck, P. Braunstein, M. Knorr, M. Strampfer and C. Strohmann, Angew. Chem., Int. Ed. Engl., 1997 (pub. 1998), 36, 2758. 107 O. G. Garkusha, B. V. Lokshin and G. K. Borisov, J. Organomet. Chem., 1998, 553, 59. 108 Y. Sun, W. E. Piers and M. Parvez, Can. J. Chem., 1998, 76, 513. 109 H. Schumann, S. Freitag, F. Girgsdies, H. Hemling and G. Kociok-Koehn, Eur. J. Inorg. Chem., 1998, 245. 110 K. Thiele, H. Go� rls and W. Seidel, Z. Anorg. Allg. Chem., 1998, 624, 555. 111 A. S. Bhanu Prasad, H. Eick and P. Knochel, J. Organomet. Chem., 1998, 562, 133. 112 M. J. Stoermer and J. T. Pinhey, Molecules, 1998, 3, M68 (online computer file); Chem. Abstr., 1998, 128, 308561w. 113 M. J. Stoermer and J. T. Pinhey, Molecules, 1998, 3, M69 (online computer file); Chem. Abstr., 1998, 128, 308562x. 114 M. J. Stoermer and J. T. Pinhey, Molecules, 1998, 3, M70 (online computer file); Chem. Abstr., 1998, 128, 308563y. 115 P. Barbaro, C. A. Ghilardi, S. Midollini, A. Orlandini, J. A. Ramirez and G. Scapacci, J. Organomet. Chem., 1998, 555, 255. 116 K. Samby, J. Kaur, G. Singh and G. S. Sodhi, Indian J. Chem., Sect. A, 1998, 37, 355. 117 L. G. Gioia, C. Santini, F. Giordano, P. Cecchi and K. Coacci, J. Organomet. Chem., 1998, 552, 31. 118 V. R. Kartashov, T. N. Sokolova, Yu. K. Grishin, N. V. Malisova and N. S. Zetirov, Russ. Chem. Bull., 1998, 47, 1574. 119 H. Layeghi, W. Tyrra and D. Naumann, Z. Anorg. Allg. Chem., 1998, 624, 1601. 120 P. B. Hitchcock, J. M. Keates and G. A. Lawless, J. Am. Chem. Soc., 1998, 120, 599. 121 M. Lutz, A. L. Spek, P. R. Markies, O. S. Akkerman and F. Bickelhaupt, Acta Crystallogr., Sect. C, 1998, 54, 1091. Annu. Rep. Prog. Chem., Sect. A, 1999, 95, 93&ndash