The Typical Elements This chapter is primarily concerned with the chemistry of the s-block and the p-block elements. For convenience it is divided up into four Parts which are dealt with by different Reporters. By F. A. HART Depaflment of Chemistry Queen Mary College Mile End Rd London El 4NS A. G. MASSEY Department of Chemistry University of Technology Loughborough Leicestershire LEI 13TU P. G. HARRISON Department of Chemistry University of Nottingham University Park Nottingham NG7 2RD J. H. HOLLOWAY Department of Chemistry Leicester University University Rd. Leicester LEI 7RH PART I Groups I IIA and IIB By F. A. HART 1 Group1 Soft-sphere ionic radii give internuclear distances in Group I and I1 halides which agree with experiment to 0.003 A.This is a considerable improvement over the conventional hard-sphere model. The internuclear Idistaye 4 is related to the cationic (M) and anionic (X)soft-sphere radii by d' =M3+X3.The soft-sphere radii for Group I and I1 metal ions are identical with metallic radii for 12-co- ordination.' The infrared spectra of Na K Rb and Cs halides condensed together with H,O or NH3 in an Ar matrix are consistent with C3,M...NH and with pyramidal Me -.OH,. In the latter case only there is H bonding to the The He(r) photoelectron spectra have been obtained of K Rb and Cs nitrates as high-temperature vapour~.~ An X-ray structure of an interesting oxide Rb7CsI1O3 shows it to contain CsI1O3 clusters (Cs as all-face-capped trigonal prism with three 0 atoms in side-face- centering positions) arranged in columns with Rb in close-packed wavy sheets * J.B.Holbrook F. M. Khaled and B. C. Smith J.C.S. Dalton 1978 1631. * B. S. Ault J. Amer. Chem. SOC.,1978 100,2426. 'B. S. Ault J. Amer. Chem. SOC.,1978 100 5773. J. D. Allen and G. K. Schweitzer Inorg. Chem. 1978,17 3418. 157 F. A. Hart A. G. Massey P. G. Harrison and J. H. Holloway between them. Within the clusters the interatomic distances are ionic but elsewhere the distances are metallic.' LizNCN crystallizes from molten lithium after the latter has been treated with N2 and Li2C2 under an Ar atmosphere at 500 'C for 150 hours. The structure (X-ray) of the resulting product shows linear NCNZ- ions approximately tetrahedrally disposed about Li' The phenyl-bridged dimer Li2Phz(MezNCHzCH2NMez)2 has been prepared and the structure (X-ray) shows that each Li is approximately tetrahedrally co-ordinated to a bidentate amine and to one carbon atom from each of two bridging phenyl groups (Li-C-Li = 67.4'; Li-C = 2.208,2.278 A).Each phenyl group lies with its plane approximately perpendicular to the Li-Li direction.8 The majority of papers dealing with Group I metals this year are concerned with their complexes with polyethers and the rest of the report deals with this topic. These ligands may be cyclic polyethers (crown ethers) non-cyclic polyethers often contain- ing other functional groups or polycyclic polyamine-polyethers which encapsulate the metal ion (cryptate ligands). Two short reviews of cryptate ligands and their complexes with Group I (and other metal ions) have appeared.'.'' Several papers deal with X-ray crystal structures of these complexes.The metal ion may or may not lie in the plane of a crown ether usually depending on the size of the metal ion compared with the ring size. In the case of the NH4+ ion (hereby made an honorary member of Group I) it lies 1.0 8 above the ring mean plane in [NH4Br( 18-crown-6)],2Hz0. Three N-H. -0 hydrogen bonds are directed downwards to three ring oxygen atoms (N to 0= 2.884,2.857 A). A Br at 2.438 8 makes up the hexagonal pyramidal co-ordination." In two Rb crown ether complexes the metal ion is also above the mean plane. In Rb2(NCS)2 (monobenzo- 18-crown-6)z each Rb is 1.24 8 above the mean plane (mean Rb-0,3.02 A) and is also bonded to two bridging N atoms from the thiocyanate ions (Rb-N=3.04 3.05 A) giving eight-co-ordination.'2 However in Rbz(NCS)z (4-nitrobenzo-18- cr0wn-6)~ where the Rb is also above the mean plane the bridging is performed by 0 atoms from the nitro groups the NCS groups being bonded (by N) to only one Rb.13 The crystal structures of the NaNCS and KNCS complexes of an open-chain polyether diol L where L = (HOC2H40-o -C6H40CH2)2 show seven-co-ordination (60+N) for the sodium complex [Na(NCS)L] but ten co-ordination (to ten 0)for the 2 :1complex of the larger potassium ion [KL2](NCS) $CHC13.14 In the dipicrate of the ion [K2L2I2+ where L = (HOOCCH20-o-C6H40CzH4)z0, each potassium ion is co-ordinated to seven 0from the unionized polyether acid and one carbonyl oxygen bridges to the other potassium ion giving a dimer with both K eight-co-ordinated (K-0 = 2.729-2.903 A).'' Lasalocid A C34Hs308 contains three ' A.Simon W. Bramer and H.-J. Deiseroth 1978 17 875. M. G. Down M. J. Haley P. Hubberstey R. J. Pulham and A. E. Thunder J.C.S. Chem. Comm. 1978 52. 'M. G. Down M. J. Haley P. Hubberstey R. J. Pulham and A. E. Thunder J.C.S. Dalton 1978 1407. D. Thoennes and E. Weiss Chem. Ber. 1978,111,3157. J.-M. Lehn Accounts Chem. Res. 1978 11,49. lo J.-M. Lehn Pure and Applied Chem. 1978,50 871. 0.Nagano A Kobayashi and Y. Sasaki Bull. Chem. Soc. Japan 1978,51,791. '* J. HaSek and K. Huml Acta Cryst. 1978 B34 1812. l3 J. HaSek K. Huml and D. Hlavata Acta Cryst.1978 B34 416. l4 D. L. Hughes and J. N. Wingfield J.C.S. Chem. Comm. 1978 1001. I' D.L.Hughes C. L. Mortimer and M. R. Truter Inorg. Chim. Acta 1978,28 83. The Typical Elements 159 hydroxyl two ether one carbonyl and one carboxylate function and can transport ions across natural and synthetic membranes. Its complex with sodium Na2- lasalocid A),(H20), has now been submitted to X-ray examination. The two organic molecules provide cavities for the two Na' ions and the two H20 molecules where one Na' is co-ordinated to six 0and one water and the other Na' ion is co-ordinated to four 0 and two water molecules.'6 The determination of stability constants and other thermodynamic parameters has formed the subject of a number of papers. Thus K AH and AS have been determined for complexation of Na' with the polyether diamide (MeCONH- 1,2- C6H40C2H4),0 in pyridine solvent with perchlorate as anion.The method used was 23Na n.m.r. studies at 5-50 "C.The values found were AH = -71 kJ mol-'; AS = 201 J mol-' K-'; K varied from lo3to 10 1mol-' depending on temperature. The complexation is thus enthaipy-driven under these conditions." The stability constants of complexes between the 2,1,1- 2,2,1- and 2,2,2-cryptates (the numbers refer to the number of 0 atoms in each chain e.g. N(C2H40C2H40C2H4)3N is 2,2,2-cryptate) and the Group I ions have been measured in methanol by competi- tion with Ag' ion. Thus for the 2,2,1-cryptate log K values are 5.4(Li); 9.6(Na); 8.5(K); 6.7(Rb) and 4.3(Cs) 1 mol-'. This specificity for Na and K arises from the rates of dissociation rather than the rates of association.The former were measured in acid solution by stopped flow or conventional conductimetry.'* The con- formation of crown ethers and diaza crowns when complexed with Group I cations has been investigated in deuteriomethanol solution by analysis of the 'H n.m.r. coupling constants. l9 Finally as a token of the continuing interest of these systems to synthetic organic chemists it is reported that Li Na and K enolates of cyclohexanone when complexed with cryptates in ether solution are powerful bases. Thus the K-2,2,2- cryptate system converts cyclohexyl chloride into cyclohexene instantly.,' 2 GroupIIA The diatomic species Mg, CaMg SrMg and SrCa which are formed by diffusion in a solid Ar matrix have been studied by electronic absorption and (with laser excitation) emission.The observations are consistent with a van der Waals ground state but a chemically bonded excited The X-ray emission X-ray photoelectron and Auger spectra of Mg(OH)2 have been obtained and are discussed in relation to a Huckel molecular orbital treatment of the bonding in this The kinetics have been studied of the second order ligand exchange reaction of the [M(edta)]'- (M =Mg Ca or Sr) complexes which exchange with edta4-. The method used was analysis of the 'H n.m.r. line shape. AH=!=,AS+ and rate constants were obtained. In the case of the Sr2' complex a first order dissociation competes with the route which follows second order kinetics.24 l6 G.D. Smith W. L. Duax and S. Fortier J. Amer. Chem. SOC.,1978,100 6725. 17 J. Grandjean P. Laszlo F. Vogtle and H. Sieger Angew. Chem. Internat. Edn. 1978.17 856. '* B. G. Cox H. Schneider and J. Stroka J. Amer. Chem. SOC.,1978,100,4747. l9 J. C. Lockhart and A. C. Robson J.C.S. Dalton 1978,611. 2o J.-L. Pierre R. le Goaller and H. Handel J. Amer. Chem. SOC.,1978 100 8021. 21 J. C. Miller and L. Andrews J. Amer. Chem. SOC.,1978,100,2966. 22 J. C. Miller and L. Andrews J. Amer. Chem. Soc. 1978,100,6956. 23 D. E. Haycock M. Kasrai C. J. Nicholls and D. S. Urch J.C.S. Dalton 1978 1791. 24 P. Mirti J. Inorg. Nuclear Chem. 1978 40 833. 160 F. A. Hart A. G. Massey P. G. Harrison and J. H. Holloway Many compounds of the new type HMgNR (R=alkyl or aryl) have been synthesised by three routes e.g.the reaction between active MgH (from MgEt,+ LiAlH4 in ether) and Mg(NR2) in THF. Infrared and molecular weight measure- ments indicate dimeric and higher association in THF with both N and H bridgesz5 Grignard analogues RSrI and RBaI can be prepared in good yields in THF at -78 ‘C. Solids can be obtained of composition RM1,n (THF) (R = Me Et Pr” Bun; n = 2 or 3). The dicyclopentadienyls of Ca Sr or Ba can be obtained in 90-100% yield by cocondensation of metal and cyclopentadiene vapour at -196 “C followed by careful warming to room temperature.26 A number of new mixed hydrido-alkyl compounds of Li and Mg have been prepared and characterised. These include LiMgHMe and LiMgH,Me.” MgH undergoes an addition reaction with alkenes in THF under the catalytic influence of cp2TiC12 giving RCH(H)-CH(MgH)R’.The products were not isolated but were detected by reaction with D20 or MgPh2(tmed) (tmed = Me,NC2H4NMe,) forms an approximately tetrahedral mole- cule where NMgN = 82.5’; CMgC = 119.4’; Mg-C = 2.167 A; Mg-N = 2.199 2.205 The structure has been determined of an interesting related complex Li2MgzPh6(tmed), which consists of linear LiMgMgLi each pair of metal atoms being bridged by a pair of Ph groups. Each Li atom is also co-ordinated by two N from tmed to complete an approximately tetrahedral co-ordination about each metal. This compound is prepared by reaction between LiPh MgPh2 and tmed.30 In X-ray crystal structure determinations co-ordination numbers of 5 and 6 have been observed for Mg” and 6 7 and 8 for Ca”.In [Mg(Me3PO)5HzO](C104)2 there is conventional octahedral co-~rdination~~ but in [Mg(Me,PO),](ClO,) the co-ordination is square pyramidal.32 In CaC12,4H20 there are two types of Ca” ion one showing octahedral co-ordination to six C1 while the other is eight-co-ordinated to seven HzO and Cl.33 CaC1N03,2H20 again has eight-co-ordinated Ca2’ to two H20 C1 two bidentate NO3 and one monodentate A number of papers have appeared on polyether complexes of the Group I1 ions including some interesting template reactions. Thus 2,6-diacetyl-pyridine conden- ses with ethylenediamine in the presence of Ca Sr or Ba salts to give complexes of the macrocyclic hexamine (1;L). The structure of [SrCl,L],2H20 has been deter- mined and shows eight-co-ordinated Sr (six Sr-N = 2.71 1to 2.744 A; two Sr-C1 = 2.915 2.927 A somewhat similar condensation of ~yridine-2~6-dialdehyde with 1,l l-diamino-3,6,9-trioxaundecane in the presence of Ca Sr or Ba(SCN) gives complexes of the macrocyclic triaminetriether (2; L’).The structure of [Ca(NCS)2L] and [Sr(NCS),L’H20] have been determined.The eight-co-ordinated Ca is in the plane of the macrocycle with Ca-0 = 2.64 8 and Ca-N = 2.64. The larger nine- *’ E. C. Ashby and A. B. Goel Znorg. Chem. 1978 17 1862. 26 B. G. Gowenlock W. E. Lindsell and B. Singh J.C.S. Dalton 1978 657. 27 E. C. Ashby and A. B. Goel Znorg. Chem. 1978,17,322. 2a E. C. Ashby and T. Smith J.C.S. Chem. Comm. 1978,30. 29 D. Thoennes and E.Weiss Chem. Ber. 1978 111 3381. 30 D. Thoennes and E. Weiss Chem. Ber. 1978 111 3726. 31 Y. S. Ng G. A. Rodley and W. T. Robinson Actu Cryst. 1978 B34 2835. 32 Y.S. Ng G. A. Rodley and W. T. Robinson Actu Cryst. 1978 B34 2837. 33 A. Leclaire and M. M. Borel Actu Cryst. 1978 B34 900. 34 A. Leclaire and M. M. Borel Actu Cryst. 1978 B34 902. 35 J. de 0.Cabral,M. F. Cabral,W. J. Cummins M. G. B. Drew A. Rodgers and S. M. Nelson Znorg. Chim. Actu 1978 30 L313. The Typical Elements co-ordinated Sr is 0.53 8 above the ring plane with Sr-0 = 2.78 8 and Sr-N = 2.78 The identity of the mean Ca or Sr interatomic distances to N and to 0is of interest; since oxygen is the smaller atom this presumably suggests that the metal-nitrogen interaction may be at least as great as the metal-oxygen interaction.A number of X-ray structures have appeared which concern crown ether complexes. Thus in [Ba(C104)2(dibenzo-24-crown-8)], the metal ion has a co- ordination number of lo$ interatomic distances Ba-0 for the ether oxygen atoms ranging from 2.76 to 3.048, while the Ba is also co-ordinated to a unidentate C104 (2.728,) and a sesquidentate C104 (2.79 and 3.30A).37 The sexidentate benzo- 18-crown-6 also complexes with Sr and Ba perchlorates giving nine-co- ordinate [Sr(benzo-18-crown-6)(H20)3](C104)2 and ten-co-ordinate [Ba(C104)2(benzo-18-crown-6)(H20)2]. In the latter complex two water molecules and one unidentate perchlorate ion are co-ordinated on one side of the crown while the other monodentate perchlorate is co-ordinated on the other side.38 The smaller cavity of benzo-15-crown-5 allows it to form a complex [Mg(NCS)2(benzo-15- crown-5)] in which the metal ion lies in the ring mean plane giving a seven-co- ordinate pentagonal bipyramid (Mg-0 = 2.171 to 2.205 A).However in the complex [Ca(NCS)2(benzo-15-crown-5)H20] the larger Ca ion lies above the crown (Ca-0 = 2.382-2.614) with two N-co-ordinated thiocyanate ions and one water molecule situated above the metal A large number of complexes of Mg Ca Sr and Ba thiocyanates with polyethylene glycols and polyethylene glycol methyl ethers have also been de~cribed.~' 3 GroupIIB More than half the papers on zinc cadmium or mercury which were published this year contain as their sole or principal feature X-ray crystal structure deter- minations.Despite this work no really novel principles have emerged but a great deal of valuable background and illustrative information has been obtained. There have been a moderate number of publications on other aspects of these three metals particularly on studies of complexation in solution. 36 D. E. Fenton D. H. Cook I. W. Nowell and P. E. Walker J.C.S. Chem. Comm. 1978 279. 37 D. L. Hughes C. L. Mortimer and M. R. Truter Actu Cryst. 1978 B34,800. D. L. Hughes C. L. Mortirner and M. R. Truter Znorg. Chim. Actu 1978 29 43. 39 J. D. Owen J.C.S. Dalton 1978 1418. 40 S. Yanagida K. Takahashi and M. Okahara Bull. Chem. SOC.Japan 1978 51,3111. 162 E A. Hart A. G. Massey P. G. Harrison and J.H. Holloway Reviews have appeared on the aqueous solution chemistry of methylmercury and its complexes4' (72 references) and on organocadmium reagents (258 reference^).^^ When ZnC12 is prepared under strictly mhydrous conditions it has an ortho- rhombic structure different from that previously reported in that although still composed of hexagonal close packed anions with zinc in tetrahedral holes the stacking sequence is altered. The original structure reappears on exposure to air." Vacuum-dehydrated Zeolite A which has been encharged with Cd2+ ions contains zero-co-ordinated Cd2+ the nearest Cd-0 contacts being shown by an X-ray structure determination to be 3.55 A."" The phase diagram of Hg12 has been rationalised by infrared and Raman evidence that the high temperature and the high pressure forms both yellow are in fact different phases."' Solution X-ray Raman and infrared studies of Zn2+ Cd2+ and Hg2+ ions in dimethylsulphoxide have shown them all to be octahedrally co-~rdinated~~ as is the case for Cd2+ and Hg2+ in the solid The stability constants of Ph3P and Ph3As towards Hg2+ in dimethylsulphoxide favour the phosphorus donor.Thus for PPh3 log K1= 11.06 log K2= 6.55; -AH = 57 -AH; = 51 kJ mol-' while for AsPh, log K1= 6.77 log K2= 2.20; -AH = 34 -AH; = 27 kJ mol-'."' With the oxygen donor Ph3P0 the standard enthalpy change AH? for the reaction MCl,(s) +2Ph3PO(s) + [MCl,(Ph3PO)J(s) has been determined by solution calorimetry to be -51.1 (Zn) -16.3 (Cd) and -12.3 kJ (Hg). The standard enthalpies of formation AH? are -587 (Zn) -528 (Cd) and -358 kJ mol-' (Hg).It is concluded that the M-0 bond enthalpies follow the sequence Zn =Cd >Hg,48 illustrating again the comparatively weak affinity of Hg2+ for oxygen donors. Complexes of the types Hg(OOCCH3)2Ln where n = 1 and 2 and L = e.g. PPh3 PPhEt, P(p-tolyl), have been described. They are non-electrolytes in nitromethane and the bisphosphine complexes dissociate in dichl~romethane"~*~~ (see also ref. 70). A number of papers have appeared on complexes of macrocyclic ligands and cryptates. Zinc tetrabenzporphyrin has been obtained in 17% yield by an easy one-step template reaction between zinc acetate aqueous ammonia and 2-acetyl- benzoic acid in the presence of molecular sieve." The X-ray structure of a related complex chloro-N-methyl-a,P,r,S-tetraphenylporphinatozinc shows irregular five-co-ordination with the N(Me)-Zn bond very weak (2.53 A) compared with the other Zn-N bonds (2.018-2.081 A); Zn-C1 is 2.232 A.52The cyclic pent- amine CH2NHC2H4NC(Me),2,6-CSH3NC(Me)NC2H4NHkH2 (L) forms the com- 41 D.L. Rabenstein Accounts Chem. Res. 1978 11 100. 42 P. R. Jones and P. J. Desio Chem. Rev. 1978,78,491. 43 H. L. Yakel and J. Brynestad Inorg. Chem. 1978 17 3294. 44 L. B. McCusker and K. Seff J. Amer. Chem. Soc. 1978,100 5052. 45 D. M. Adams and R. Appleby Znorg. Chim. Acta 1978 26 L43. 46 M. Sandstrom I. Persson and S. Ahrland Acta Chem. Scand. 1978 A32 607. 47 S. Ahrland T. Berg and P. Blauenstein Acta Chetn. Scand. 1978 A32 933. 48 R.A. Jorge C. Airoldi and A. P. Chagas J.C.S. Dalton 1978 1102. 49 E. C. Alyea and S. A. Dias Canad. J. Chem. 1978 56 83. 50 T. Allman R. G. Goel and P. Pilon Canad. J. Chem. 1978 56,91. A. Vogler and H. Kunkely Angew. Chem. Znternat. Edn. 1978 17 760. 52 D. K. Lavallee A. B. Kopelove and 0.P. Anderson J. Amer. Chem. Soc. 1978 100 3025. The Typical Elements 163 -plex Cd(C104)2L which contains chains * * (CdL)C104(CdL)C104 -. Each C104- ion bridges two Cd by two of its 0 atoms one to each Cd. The co-ordination is thus pentagonal bi~yramidal.'~ In contrast to this cyclic quinquedentate ligand the acyclic potentially quinquedentate 2,6-C5H,N{C(Me)N.o-C6H4SMe}2 (L') forms a complex Cd12L' which is five-co-ordinated the two S atoms being free.The co-ordination is trigonal bipyramidal distorted because N-Cd-N is constrained to -68" (Cd-N = 2.33-2.41; Cd-I = 2.713 2.726 The complexes [ZnXL"]' where X = C1 Br I NCS C104 and L = ( -CH2NMeCH2CH2NMeCH2-)2 have been examined by variable-temperature 13C n.m.r. in CH3N02 and by X-ray determination (solid; X = Cl). In the latter case the co-ordination is square pyra- midal but the n.m.r. results are interpreted in terms of interconversion between two equivalent trigonal bipyramidal forms two N atoms from the cyclic tetramine being In a wide-ranging survey of stability constants between metal ions and the cryptate ligand N(CZH40C2H40C2H4)3N and related ligands where up to four oxygen atoms are replaced by NMe groups it was found that these ligands are very selective particularly for Hg2+ (log K = 18-27) but also for Cd2+ (7-12) and Zn2' (3-1 l),compared with for example K' (2-5) or Ca2' (2-5).56 In the organometallic area 'H n.m.r.has shown that the compounds ZnR2 (R = allyl 2 or 3-methylallyl 3,3-dimethylallyl) are dynamic mixtures of all isomeric ?'-ally1 forms at room temperature. Interconversion ceases below -115 OC." The triad M(CH2SiMe3)* (M= Zn Cd or Hg) has been completed by the synthesis of the Cd member by a Grignard reaction. It is thermally stable complexes with 2,2'- dipyridyl and 1 10-phenanthroline and reacts immediately with oxygen or water.58 Complex formation between CH3Hg+ and C1- Br- or NO3- in water has been studied by radiometry using 203Hg in a waterlo-xylene system and K values were obtained e.g.log Kc,-= 5.64.59 In the very popular field of X-ray crystallographic studies those of mercury predominate. We give here a selection following the sequence zinc cadmium and mercury. Zinc iodide whose structure has not been previously determined is tetragonal and shows nearly regular tetrahedral co-ordination of zinc with Zn-I = 2.58 to 2.68 Most zinc structures reported this year involve near-tetrahedral co- ordination with sulphur ligands e.g. [Zn(thiourea),](N03) (Zn-S = 2.324-2.361 and (Ph4P)2[Zn(SPh)]4 where the tetrahedron is distorted by up to 12" owing to compression along a twofold axis the analogous cadmium compound being closely similar.62 (PPh4)2[Zn(WS4)2] has [S2WS2ZnS2WS2I2- ions where the co- ordination of both Zn and W is near-tetrahedral (S-Zn-S = 96.7" and 116.2°).63 53 M.G. B. Drew S. Hollis S. G. McFall and S. M. Nelson J. Znorg. Nuclear Chem. 1978,40 1595. 54 M. G.B. Drew and S. Hollis Actu Cryst. 1978 B34 2853. 55 N. W. Alcock N. Herron and P. Moore J.C.S. Dalton 1978 1282. 56 J.-M. Lehn and F. Montavon Helv. Chim. Actu 1978,61 67. " R. Benn E. G. Hoffrnann H. Lehrnkuhl and H. Nehl J. Orgunometullic Chem. 1978,146 103. '' D. M. Heinekey and S. R. Stobart Znorg. Chem. 1978,17 1463. 59 M. Jawaid F. Ingrnan D. H. Liem and T. Wallin Acta Chem. Scand. 1978 A32 7. 6o P.H.Fourcroy D. CarrC and J. Rivet Actu Crysr. 1978 B34 3160. 61 R. Vega A. Lbpez-Castro and R. Marquez Actu Cryst. 1978 B34 2297. 62 D. Swenson N. C. Baenziger and D. Coucouvais J.Amer. Chem. Soc. 1978,100 1932. 63 I. Paulat-Boschen B. Krebs A. Miiller E. Koniger-Ahlborn H. Dornfeld and H. Schulz Znorg. Chem. 1978,17 1440. 164 F. A. Hart A. G. Massey P. G. Harrison and J. H. Holloway Cadmium structure determinations are rather few but include CdBr2(H20)4 where the Cd2+ ion in -CdBr2CdBr2. -chains is co-ordinated trans-octahedrally to four Br and two H20 (Cd-Br = 2.746;Cd-0 = 2.349A),64and [Cd(Me2SO),]- (C1O,J2which shows nearly octahedral co-ordination (0-Cd-0 = 84.5"-95.3"; Cd-0 = 2.257-2.278 A).65 Mercury(I1) is known to display a range of co-ordination numbers and geometries. It particularly favours 2,4,and 6,and in the last case shows a tendency to form two short colinear and four longer bonds (2+4co-ordination).These tendencies are well illustrated in the year's structures. Taking the simpler compounds first NEt4HgC13 shows 3+2 co-ordination. Triangular HgC13 entities (Hg-Cl= 2.426-2.444 A) are so arranged that two further long (3.054 3.017 A) bonds complete a trigonal bipyramid.66 When K2X and HgX (X = Sor Se) are heated to 360-780 "C yellow to reddish-orange K6HgX4 is obtained. The sulphur compound has nearly tetrahedral Hg (Hg-S = 2.542or 2.591A).67 Nearly octahedral co-ordination is shown by both [Hg(H20)6](C104)2 (Hg-0 = 2.341A; 0-Hg-0 = 85.8' 94.2°)68and by [Hg(Me2SO)6](ClO4)2 (Hg-0 = 2.317-2.376 which thus resembles its cadmium analogue mentioned above. However the tendency to the 'x short +y long' type of co-ordination is shown again in two other structures.[Hg(CH,COO),(P'Bu,)] has irregular five-co-ordination between Hg and P (2.371A) two nearer 0 (2.25,2.27A) and two further 0 (2.58 2.66A) from the unsymmetrically bidentate acetate gro~ps.'~ In Hg(CF,COO) (~yridine)~ we get pentagonal bipyramidal (2+5) co-ordination. Here there is a N-Hg-N axis (170.2'; 2.11 2.13A) with five 0from two bidentate and one (bridging) unidentate acetate groups (Hg-0 = 2.56-2.87 A) within at most 0.1638,of the best equatorial plane.71 In some organo-mercury complexes the tendency to '2+y ' co-ordination is quite marked. In CH,Hg(NO3)(3,3'-dimethyl-2,2'-bipyridyl) the diamine is unidentate only giving a C-Hg-N backbone (172.7";Hg-C = 2.01,Hg-N =2.11 A) which interacts with four nitrate 0 atoms (2.84-3.09 A) and may also interact with the second aromatic ring of the diamine (Hg-C = 3.11 A).72In [PhHgCN(1,10- phenanthro!ine)] there is a nearly linear (167.5') Ph-Hg-CN group (Car-Hg = 2.067A CcN-Hg = 2.063A) to which is co-ordinated the diamine (Hg-N = 2.660 2.680 A) such that the triangle HgN2 is approximately perpendicular to C-Hg-C to give a curious unsymmetrical structure where the C-Hg-C angle has resisted distortion to a pseudo-tetrahedral angle.73 Lastly in [MeHg(pyridine)]N03 the secondary bonds have become non-existent (Hg-0 = 3.16and greater) leaving two-cordinate Hg in the Me-Hg-py grouping (179.7";Hg-C = 2.04,Hg-N = 2.12 64 H.Leligny and J. C. Monier Acta Cryst. 1978 B34 5. 6s M. Sandstrom Acta Chem. Scand. 1978 A32 519. 66 M. Sandstrom and D.H. Liem Acta Chem. Scand. 1978 A32 509. 67 H. Sommer and R. Hoppe 2.anorg. Chem. 1978,443,201. 68 G. Johanson and M. Sandstrom Acta Chem. Scand. 1978 A32 109. 69 M. Sandstrom and 1. Persson Acta Chem. Scand. 1978 A32,95. 70 P. J. Roberts G. Ferguson R. G. Goel W. 0.Ogini and R. J. Restivo J.C.S. Dalton 1978 253. 71 J. Halfpenny R. W. H. Small and F. G. Thorpe Acta Cryst. 1978 B34 3075. 72 A. J. Canty N. Chaichit B. M. Gatehouse and A. Marker Acta Cryst.,1978 B34 3229. 73 A. Ruiz-Amil S. Martinez-Cartera and S. Garcia-Blanco Acta Cryst. 1978 B34 2711. 74 R. T. C. Brownlee A. J. Canty and M. F. Mackay Austral. J. Chem. 1978,31 1933.