David G. Evans

Platinum metal complexes of potentially chelating alkene–sulphur and alkene–selenium ligands. The synthesis by chalcogen dealkylation and X-ray structures of the dimeric complexes [{PtI(SCH2CH2CMeCH2)}2] and [{PtI(PPh3)(SCH2CH2CMeCH2)}2], and a dynamic nuclear magnetic resonance study of [{PtI(L)(SCH2CH2CMeCH2)}2][L = PPh3, PPh2Me, or As(CH2SiMe3)3]

The chelating ligands 2,8-dimethyl- 5-thianona-1,8-diene and 2,8-dimethyl-5-selenanona-1,8-diene have been found to undergo unusually facile chalcogen dealkylation on treatment with halide when co-ordinated to platinum(II). The resulting dimeric complexes contain chelating bridging alkenyl thiolato and alkenyl selenato ligands and have been fully characterised. An X-ray diffraction study of [{PtI(SCH2CH2CMeCH2)}2] is reported: the crystals are orthorhombic, space group Pbca with Z= 1 in a unit cell of dimensions a= 12.733(3), b= 15.288(2), and c= 16.904(3)A. The molecular structure involves a non-planar Pt2S2 ring, with square-planar co-ordination at each platinum being completed by the chelating alkene and iodide ligands. The principal internuclear distances are Pt(1)–I(1) 2.624(2), Pt(2)–I(2) 2.621(2), Pt(1)–S(1) 2.295(6), Pt(1)–S(2) 2.330(6), Pt(2)–S(1) 2.334(6), Pt(2)–S(2) 2.304(6), Pt(1)–C 2.216(25) and 2.21 (3), Pt(2)–C 2.207(24) and 2.155(23)A. The co-ordinated alkene functions are displaced by ligands containing Group 5A donor atoms yielding dimeric complexes which contain non-chelating bridging alkenyl thiolato and alkenyl selenato ligands and which have been fully characterised. Inversion of configuration at the bridging chalcogen atom is observed at moderate temperatures and has been studied by dynamic n.m.r. spectroscopy. An X-ray diffraction study of [{PtI(PPh3)-(SCH2CH2CMeCH2)}2] is reported: the crystals are triclinic, of space group P, with Z = 1 in a unit cell of dimensions a= 10.396(1), b= 11.250(5), and c= 13.348(2)A with α= 91.63(3)β= 94.53(1), and γ= 116.02(3)°. The molecular structure involves a planar Pt2S2 ring, with square-planar co-ordination at each platinum being completed by triphenylphosphine and iodide ligands. The molecule has a centre of inversion. The principal internuclear distances are Pt–I 2.621 (1), Pt–S 2.367(3), and Pt–P 2.267(3)A.

Molecular orbital analysis of the bonding in some triangular platinum clusters with 42 to 48 valence electrons

Abstract The electronic and structural features of triangular platinum clusters have been analysed by Extended Huckel molecular orbital calculations. The prevalence of planar triangular clusters with a 42 electron count is rationalised, and the way in which the cluster bonding orbitals are markedly stabilised by edge-bridging ligands is discussed in terms of a general model. In such such clusters, the metal p orbitals play a minor role, but the calculations indicate how incorporation of out of plane capping carbonyl ligands induces a greater role for these p orbitals and facilitates the formation of clusters with electron counts of between 42 and 48. The calculations lead to a rationalisation of the way in which the synergism between ligand orbitals on opposite sides of the metal triangle determines the detailed structural features observed in a series of clusters based on the [Pt 3 (dppm) 3 ] core, recently reported by Puddephatt.

Platinum metal complexes of potentially chelating alkene-thioether and -selenoether ligands: Synthesis of the trimeric complexes [RhCl{E(CH2CH2CHCH2)2}]3 (E S, Se) and the crystal structure of [RhCl{Se(CH2CH2CHCH2)2}]3

Reaction of [{RhCl(C 2 H 4 ) 2 } 2 ] with E(CH 2 CH 2 CHCH 2 ) 2 (E = S, affords the trimeric complexes [RhCl{E(CH 2 CH 2 CHCH 2 ) 2 }] 3 . The structure of the product with E = Se was established by X-ray diffraction. The coordination sphere at each rhodium atom consists of a distorted trigonal bipyramid with two alkene groups from the same selenoether in equatorial positions, one bridging selenium in the third equatorial position and the other in an axial site with a terminal chloride in the other axial site. One- and two-dimensional NMR studies of the compounds suggest that the solid state structure is retained in solution.

Dimethylplatinum complexes of polydentate alkene–sulfur and –selenium ligands

Interaction of [PtMe2(SMe2)2] with 1 equivalent of 5-selenanona-1,8-diene produces a monomeric complex containing the ligand chelating through one alkene moiety and the selenium atom. The unco-ordinated alkene moiety undergoes exchange with the co-ordinated alkene moiety which has been studied by dynamic NMR spectroscopy. Interaction of the same platinum(II) precursor with 0.5 mol equivalent of the dialkenyl chalcogenoether ligands E(CH2CH2CHCH2)2(E = S or Se) produced the novel dinuclear complexes [Pt2Me4{µ-E(CH2CH2CHCH2)2}] both of which have been characterised by X-ray crystallography and shown to be isostructural. The unit cells are of dimensions a= 10.850(2), b= 11.289(7) and c= 12.415(1)(E = S) and a= 11.056(1), b= 11.251(1) and c= 12.546(2)A, (E = Se). In each case the two metals are bridged by a tetrahedrally co-ordinated chalcogen atom, with one alkenyl group chelating to each platinum atom. The platinum–chalcogen distances are Pt–S 2.354(8) and Pt–Se 2.457(5)A.

Molecular orbital analysis of the bondig in platinum phosphine hydride clusters

The electronic and structural features of platinum clusters containing tertiary phosphine and hydride ligands have been analysed using Extended Huckel molecular orbital calculations. The calculations illustrate how the non-conical nature of the constituent PtL2 fragments leads to their having a marked conformational preference in the clusters. The introduction of PtL fragments into some of the clusters leads to a further flexibility in electron count which may also be rationalised on the basis of the analysis presented here.

Molecular structure of gaseous titanium tris(tetrahydroborate), Ti(BH4)3: experimental determination by electron diffraction and molecular orbital analysis of some Ti(BH4)3 derivatives

The structure of gaseous titanium tris(tetrahydroborate) has been determined by analysis of the electron diffraction patterns due to the molecules Ti(BH4)3 and Ti(BD4)3. The molecule has thus been shown to possess three tridentate BH4 groups generating a structure with C3h symmetry overall, implying nine-fold co-ordination of the titanium atom and a planar TiB3 skeleton. With the assumption of local C3v symmetry for each Ti(BD4) fragment, salient structural parameters (ra) are as follows: r(Ti ⋯ B) 217.5(0.4), r(Ti–Db) 198.4(0.5), r(B–Db) 127.6(0.5) and r(B–Dt) 116.6(1.3) pm; and within each Ti(BD4) fragment Db–Ti–Db 60.1(0.7) and Db–B–Db 102.4(0.6)°. Such a structure is consistent with the IR and UV photoelectron spectra of the molecule in the gaseous or matrix-isolated states, but aggregation occurs in the condensed phases (e.g. in solution in a non-polar solvent or in the solid state). The structural properties of the Ti(BH4)3 molecule are compared with those of related tetrahydroborate derivatives, and the factors influencing these properties are assessed in terms of elementary symmetry and perturbation-theory arguments, supported by extended Huckel molecular orbital calculations.

Language development in Down's Syndrome retardates: A factorial study

Abstract One hundred and one Downs Syndrome retardates were given a battery of language and cognitive tests. The resulting intercorrelations were factor analyzed using Principal Components, Varimax Rotation, and Promax procedures. Chronological age was included as one of the variables in the analysis. The resultant factors are described and discussed.