Damian R. Aris

STRUCTURAL CHEMISTRY OF SC(III) : AN OVERVIEW

Abstract Structural aspects of the chemistry of organometallic/coordination compounds of scandium(III) are reviewed. Individual compounds are classified and discussed in terms of coordination number and associated metal geometry through the range CN=3–9. The present review provides an exhaustive literature coverage 1926–1998 (April).

Ge(IV)–citrate complex formation: synthesis and structural characterisation of GeCl4(bipy) and GeCl(bipy)(Hcit) (bipy=2,2′-bipyridine, H4cit=citric acid)

Abstract The adduct [GeCl4(bipy)] (I), obtained by direct treatment of the parent halide with 2,2′-bipyridine (bipy), reacts with citric acid (H4cit) in acetonitrile solution to provide the chelate derivative [GeCl(bipy)(Hcit)] (II). The structures of compounds I and II have been determined by single crystal X-ray diffraction. For I the central germanium shows octahedral geometry with two mutually cis-chlorine atoms, GeCl (mean) 2.244(1) A, and the bidentate ligand, GeN (mean) 2.065(4) A occupying equatorial positions and two mutually trans-chlorine atoms, GeCl (mean) 2.267(1) A in axial locations. For II the citrate ligand is terdentate and bound to the central germanium via its hydroxyl, α-carboxylate and one of the β-carboxylate groups in a fac-octahedral arrangement. GeOhydroxyl 1.800(3) A, GeOcarboxylate (mean) 1.904(3) A, GeCl 2.209(1) A, GeN (mean) 2.012(3) A. The uncoordinated β-carboxylate group remains intact as a ‘dangling arm’. The structure also contains poorly defined and disordered acetonitrile (solvent) molecules trapped in the lattice.

Adducts of indium(III) bromide: synthesis and structural characterisation of [InBr3(THF)2], [InBr3(DMF)3], [InBr3(Me3[9]aneN3)] and [InBr3({–N(Me)–CH2–}3)]

Abstract Treatment of InBr3 with THF gives InBr3(THF)2. A crystal structure determination (X-ray diffraction) reveals that the five co-ordinate metal centre adopts a trigonal bipyramidal geometry with the three halogen atoms in the equatorial plane and the two THF ligands in axial positions. Cremer–Pople ring puckering analysis reveals one THF ligand in a twist conformation and the other in an envelope arrangement in each molecule. The reaction of InBr3 with DMF in hexane gives InBr3(DMF)3 identified (spectroscopic and X-ray diffraction) as the six co-ordinate fac-octahedral isomer. Treatment (1:1 in acetonitrile) of InBr3 with 1,4,7-trimethyl-1,4,7-triazacyclononane gives InBr3(Me3[9]aneN3) in which the anticipated facial co-ordination of the terdentate ligand results in a distorted octahedral geometry at the metal centre as confirmed by X-ray diffraction. Similar treatment of InBr3 with 1,3,5-trimethyl-1,3,5-triazacyclohexane gives InBr3({–N(Me)–CH2–}3) as verified by spectroscopic analyses and an X-ray diffraction study.

Crown ether complexation of p-block metal halides: synthesis and structural characterisation of [InI2(dibenzo-24-crown-8)(H2O)][InI4], [(SnBr4)2(dibenzo-24-crown-8)]·MeCN, [(SbCl3)2(dibenzo-24-crown-8)]·MeCN, [(BiCl3)2(dibenzo-24-crown-8)]·MeCN and [(SbBr3)2(dibenzo-24-crown-8)]

Abstract The reactions of the large crown ether 6,7,9,10,12,13,20,21,23,24,26,27-dodecahydrodibenzo[b,n][1,4,7,10,13,16,19,22]octaoxycyclotetracosine (dibenzo-24-crown-8) with p-block metal halides have been studied, leading to the isolation and structural characterisation of [InI2(dibenzo-24-crown-8)(H2O)][InI4] (I), [(SnBr4)2(dibenzo-24-crown-8)]·MeCN (II), [(SbCl3)2(dibenzo-24-crown-8)] (III), [(BiCl3)2(dibenzo-24-crown-8)]·MeCN (IV) and [(SbBr3)2(dibenzo-24-crown-8)]·MeCN (V). Compound I was isolated as colourless block crystals; crystals are triclinic, space group P1, Z=2, R=0.0372. The structure consists of [InI2(dibenzo-24-crown-8)(H2O)]+ cations and [InI4]− anions. For the cation, the threaded near-linear InI2+ unit (InI 2.6977(5), 2.6919(5) A) is located off-centre within the cavity and is bonded to four ring oxygen atoms (InOcrown 2.344(4)–2.560(4) A) and a single water molecule (InOwater 2.271(4) A). The latter forms intracavity hydrogen bonds of the type MOH2⋯Ocrown to two more of the oxygen atoms of the crown (Owater⋯Ocrown 2.89, 2.94 A). Compound II was isolated as orange block crystals; crystals are monoclinic, space group I2/m, Z=2, R=0.0391. The structure features the two metal centres in exocyclic locations each bound to two oxygens of the ring (SnOcrown 2.262(3) A). The metal geometry is distorted octahedral (SnBr 2.5235(7), 2.5187(6) A). Compound III was isolated as colourless block crystals; crystals are monoclinic, space group C2/c, Z=4, R=0.0311. The two SbCl3 moieties (SbCl 2.3807(8), 2.3874(8), 2.4015(9) A) are coordinated to opposite sides of the crown which adopts a sigmoidal conformation to create two O5 donor cavities. Each Sb(III) centre is bound to five oxygens of the ring (SbOcrown 2.852(2)–3.153(2) A). Crystals of IV are monoclinic, space group C2/c, Z=4, R=0.0325. The structure is directly similar to that of III with two BiCl3 units (BiCl 2.5034(12), 2.5054(13), 2.5389(12) A) coordinated to opposite sides of the ring which exhibits a sigmoidal conformation. Each Bi(III) centre is bonded to five crown oxygen atoms (BiOcrown 2.733(3)–3.221(4) A). Compound V crystallises in the triclinic space group P1, Z=2, R=0.0693. The two SbBr3 groups are located on opposite sides of the ring (SbBr 2.5268(15), 2.5478(15), 2.5558(14) A) and each one is bound to four of the ring oxygen atoms (SbOcrown 2.893(7)–3.183(8) A).

N,N′-Unsubstituted amidinato metallacycle complexes of Group 13 metal alkyls: the crystal structure of trimeric [{Me2Al(μ-HNCPhNH)}3]

Abstract The amidinato complexes [Me 2 ML] (L=HNCPhNH, M=Al, Ga, In; L=HNCBu t NH, M=Ga) result from the reaction of the trialkylmetal with an equimolar amount of the amidine. MS data indicate that the complexes exist as dimers or trimers in the gas phase. X-ray crystallographic studies on [{Me 2 Al(μ-HNCPhNH)} 3 ] ( 1 ) reveal a novel trimeric structure in the solid state, with bridging benzamidinato ligands, and a 12-membered metallacycle. Reaction of InMe 3 with two moles of benzamidine yields a cyclic imidoylamidinato derivative with a six-membered [InNCNCN] ring.

Halide abstraction from Pr(III) chloride by Sn(IV): formation and crystal structures of [Pr(MeCN)9][SnCl5(THF)]2.5[SnCl5(MeCN)]0.5, [Pr(MeCN)9][SnCl5(MeCN)]3 and [PrCl2(THF)5][SnCl5(THF)]: identification of structural isomers of the nine co-ordinate [Pr(MeCN)9]3+ cation

Abstract Treatment of PrCl3 with SnCl4 and dibenzo-24-crown-8 in MeCN/THF (60/40) afforded [Pr(MeCN)9][SnCl5(THF)]2.5[SnCl5(MeCN)]0.5 (I) as the only isolated product. From the crystal structure determination (X-ray diffraction) the nine co-ordinate Pr atom adopts a tricapped trigonal prismatic geometry with PrN bond distances in the range (2.577(4)–2.615(5) A), whilst one of the three Sn(IV) counteranions has half-occupancy between THF and MeCN at the solvent position. Subsequent investigation of the PrCl3/SnCl4/S (solvent) system reveals that with S=MeCN complete halide abstraction leads to the formation of [Pr(MeCN)9][SnCl5(MeCN)]3 (II), regardless of the stoichiometry employed. In this case the cationic Pr metal centre adopts a slightly distorted mono-capped square prismatic geometry with PrNprism bond distances (2.583(9), 2.502(9) A) and PrNcapping (2.645(17) A). Conversion of the (idealised) monocapped square prismatic isomer (II) to the tricapped trigonal prismatic isomer (I) is discussed. Treatment of PrCl3 with SnCl4 with S=THF leads to the formation of [trans-PrCl2(THF)5][SnCl5(THF)] (III) in which the cation is seven co-ordinate and features a trans-PrCl2 unit (axial) PrCl (2.6767(9) A) with five THF molecules in an equatorial girdle to give a pentagonal bipyramidal metal geometry PrO (2.467(4)–2.489(3) A).

Ligand oxidation of small-ring aza- and thia-macrocycles involving CH activation: crystal structures of [MeN(CH2NMe)2CH]2[MX6]·MeCN (M=Te, X=Cl, Br; M=Sn, X=Br and [C6H11S3]2[TeBr6]·MeCN)

Abstract Reactions of M(IV) halides with the six-membered triazacyclohexane (MeNCH 2 ) 3 provide the ionic salts [MeN(CH 2 NMe) 2 CH] 2 [MX 6 ]·MeCN where M=Te, X=Cl ( I ); M=Te, X=Br ( II ) and M=Sn, X=Br ( III ), as confirmed by spectroscopic and single crystal X-ray diffraction studies. The individual [MeN(CH 2 NMe) 2 CH] + cations contain a planar (Me)NCHN(Me) segment reminiscent of amidinium formation (mean): NC, 1.31(1) A; NCN, 123.3(1)°. A plausible reaction pathway involving an incipient release of a hydride ion from a CH 2 unit of the bound ligand and a subsequent attack (nucleophilic) at the β-carbon of a coordinated acetonitrile (solvent) molecule is discussed. Supporting evidence for activation of the acetonitrile via a nucleophilic attack comes from the reaction system GeBr 4 / i C 3 H 7 NHCOCH 2 CONH i C 3 H 7 /CH 3 CN, which provides the cationic organohydrobromide salt [CH 3 C(CH(CONH i C 3 H 7 ) 2 ) 2 NH 3 ]Br ( IV ). The structure of IV reveals two malonamide fragments attached to the acetonitrile residue. The reaction of TeBr 4 and [9]aneS 3 provides orange crystals of a product identified spectroscopically and by X-ray diffraction studies as the bicyclic sulphonium salt [C 6 H 11 S 3 ] 2 [TeBr 6 ]·MeCN ( V ). A plausible reaction pathway, namely molecular oxidation with CH activation resulting in hydride ion expulsion, is suggested. The structure of the bicyclic cation reveals a five-membered ring and a six-membered ring fused along a common SC linkage, 1.825(6) A. The peripheral SC bond distances lie in the range 1.800(5)–1.822(5) A. The reaction of TeCl 4 and Me 3 [9]aneN 3 in toluene gives orange crystals of the doubly-protonated ligand salt [(Me 3 [9]aneN 3 )H 2 ][TeCl 6 ]·C 6 H 5 CH 3 ( VI ). An extensive pattern of intra- and inter-molecular hydrogen bonding is observed.

Metallacycles of the imidoylamidinato compounds HNC(R)NC(R)NH and Group13 elements. Crystal structure of the complex [GaMe2{HNC(CF3)NC(CF3)NH}]

Reaction of trimethylgallium with trifluoroacetamidine [H 2 NC(CF 3 )NH] resulted in an unusual elimination reaction, and yielded the air-stable volatile metallacycle [GaMe 2 {HNC(CF 3 )NC(CF 3 )NH}] which shows a planar six-membered (GaNCNCN) ring; a related aluminium system [AlMe 2 {HNC(Ph)NC(Ph)NH}] was formed using benzamidine [H 2 NC(Ph)NH].

Identification of the cobalt(II) chloride ‘mixed’ solvate Co4Cl8(H2O)4(MeCN)6: the ionic structure trans-[Co(H2O)2(MeCN)4] trans-[Co(H2O)2(MeCN)2(CoCl4)2]

The structure of the title compound features mononuclear octahedral CoII cations, trans-[Co(H2O)2(MeCN)4]2+, and trinuclear anions, trans-[Co(H2O)2(MeCN)2(CoCl4)2]2−; the latter centrosymmetric units contain a central octahedral Co(H2O)2(MeCN)2 moiety with two tetrahedral [CoCl4]2− ligands. These two large ions are held in a network of intra- and inter-molecular hydrogen bonding.

Bis(N,N′-di­phenyl­acetamidinato)­ethyl­indium(III)

The title compound, [In(C2H5)(C14H13N2)2], contains an InIII atom in a square-pyramidal geometry. The phenyl rings are almost coplanar in one of the amidinate ligands but significantly twisted with respect to each other in the other ligand.