George A. Forsyth

A near-planar pentadentate silver(I) complex; the crystal and molecular structure of (2,2′ : 6′,2″ : 6″,2‴ : 6‴,2â—-quinquepyridine)silver(I) hexafluorophosphate

The complex [AgL1][PF6](L1= 2,2′ :6′,2″ :6″,2‴ : 6‴,2â�—-quinquepyridine) has been prepared and structurally characterised; in contrast to the double helical binuclear complexes formed with first row transition metal ions, the title complex is mononuclear, with a near-planar arrangement of the ligand about the metal, and the cation exhibits weak π-interactions with adjacent cations, but there is no direct Ag–Ag interaction.

Determination of the molecular structure of tris(trimethylsilyl)phosphine in the gas phase by electron diffraction, supported by molecular mechanics calculations

Abstract The molecular structure of tris(trimethylsilyl)phosphine in the gas phase has been determined by electron diffraction. Results of three refinements are reported. In the first refinement, overall C 3 symmetry and local C 3 symmetry for the SiMe 3 groups were assumed, but these groups were allowed to tilt away from one another so that their C 3 local axes no longer coincided with the PSi bonds. The major geometrical parameters were r a (PSi) 225.9 (1), r (SiC) 188.2(1) pm, ∠ SiPSi 105.1(2) and ∠ CSiC 107.9(1)°. The tilt angle was 5.9(3)°, and the SiMe 3 groups were twisted 17.2(2)° away from the staggered position, at which the overall molecular symmetry was C 3v ; the PSiC angles were therefore 106.8, 109.3 and 116.7°. In the other two refinements the restriction of C 3 symmetry within the SiMe 3 groups was removed, and the differences between SiC distances and between CSiC angles were first fixed at values calculated by molecular mechanics (MM2), and then these new restrictions were partially relaxed. Neither of these refinements fitted the experimental data quite as well as the first one.

Correlation of the redox properties and stereochemical features of copper complexes of [18]aneN2S4(1,4,10,13-tetrathia-7,16-diazacyclooctadecane) and its N,N′-dimethyl derivative Me2[18]aneN2S4. Crystal structures of [CuII([18]aneN2S4)][ClO4]2·H2O, [CuII(Me2[18]aneN2S4)][PF6]2, [CuI2([18]aneN2S4)]BPh4, [CuI(Me2[18]aneN2S4)]PF6 and [CuI2(Me2[18]aneN2S4)(NCMe)2][PF6]2

Reaction of copper(II) salts with L =[18]aneN2S4(1,4,10,13-tetrathia-7,16-diazacyclooctadecane) or its 7,16-dimethyl derivative Me2[18]aneN2S4 affords the cations [CuL]2+ in high yields. The complex [Cu([18]aneN2S4)][ClO4]2·H2O crysatallises in the orthorhombic space group Pcab with a= 12.020(8), b= 17.733(17), c= 21.999(23)A and Z= 8. A single-crystal structure determination has shown the CuII to be bound via all six macrocyclic donors atoms to give a tetragonally compressed octahedral stereochemistry, Cu–S(1) 2.577(5), Cu–S(4) 2.487(5), Cu–S(10) 2.528(5), Cu–S(13) 2.578(5), Cu–N(7) 2.007(13) and Cu–N(16) 2.036(12)A, with the macrocycle in a rac configuration. The complex [Cu(Me2[18]aneN2S4)][PF6]2 crystallises in the trigonal space group Pm1, a= 10.5140(4), c= 6.6604(5)A and Z= 1. The CuII occupies a site of D3d symmetry, bound to the six macrocyclic donor atoms to give a tetragonally elongated octahedral stereochemistry in a meso configuration, Cu–S 2.496(5) and Cu–N 2.191(17)A. The ion [Cu([18]aneN2S4)]2+ shows a reversible CuII–CuI redox couple at E½=–0.31 V vs. ferrocene–ferrocenium, while that for [Cu(Me2[18]aneN2S4)]2+ occurs at a more anodic potential, E½=+0.06 V. The diamagnetic copper(I) species [CuL]+ can be generated electochemically from the copper(II) precursors by controlled-potential electrolysis, although the direct route via reaction of [Cu(NCMe)4]+ with 1 molar equivalent of L in refluxing MeOH under N2 is better. The complex [Cu(Me2[18]aneN2S4)]PF6 crystallises in the triclinic space group P, a= 10.3386(23), b= 10.7643(25), c= 12.054(3)A, α= 102.450(9), β= 113.951(11), γ= 102.692(10)° and Z= 2. The CuI is bound via three macrocyclic S- and one macrocyclic N-donor atom, Cu–S 2.2516(16), 2.2612(16), 2.3342(17), Cu–N 2.175(5)A, giving a distorted-tetrahedral stereochemistry. The complex [Cu([18]aneN2S4)]BPh4 crystallises in the orthorhombic space group P212121, with a= 12.270(4), b= 14.314(8), c= 19.914(5)A and Z= 4. The structure is very similar to that of [Cu(Me2[18]aneN2S4)]+ with the CuI bound via three S- and one N-donor atom, Cu–S 2.250(3), 2.245(3), 2.357(4), Cu–N 2.121(9)A, giving a distorted-tetrahedral stereochemistry. The differences in potentials for the CuII–CuI couples in [Cu([18]aneN2S4)]2+/+ and [Cu(Me2[18]aneN2S4)]2+/+ are therefore due to the different configurations, meso and rac, in the parent copper(II) species rather than to differences in the copper(I) structure. Reaction of Me2[18]aneN2S4 with 2 molar equivalents of [Cu(NCMe)4]+ affords the binculear copper(I) species [Cu2(Me2[18]aneN2S4)(NCMe)2]2+ the PF6– salt of which crystallises in the triclinic space group P, a= 7.3435(18), b= 11.0562(3), c= 11.824(3)A, α= 62.298(10), β= 81.904(15), γ= 82.764(16)° and Z= 1. The cation lies across an inversion centre, with each CuI bound via two macrocyclic S- and one macrocyclic N-donor atom, Cu–S 2.317(4), 2.286(4), Cu–N 2.165(7)A, with an NCMe solvent molecule completing the distorted-tetrahedral stereochemistry, Cu–N 1.924(9)A.

Stereochemical and electronic control of the copper(II)/(I) couple by N2S4-donor macrocycles

The N2S4 donor complex [Cu(L1)]2+(L1= 1,4,10,13-tetrathia-7,16-diazacyclo-octadecane) shows a chemically reversible copper (II)/(I) couple at E½–0.31 V vs. Fc/Fc+(ferrocene/ferrocenium), whereas the methylated analogue, [Cu(L2)]2+(L2= 7,16-dimethyl-1,4,10,13-tetrathia-7,16-diazacyclo-octadecane) shows a more anodic copper(II)/(I) couple at E½+ 0.06 V vs. Fc/Fc+˙; these differences in redox potential can be related to the stereochemical features of the copper(II) complexes, the crystal structures of which have been determined for [Cu(L1)]2+ and [Cu2(L2)(NCMe)2]2+.

Determination of the gas-phase molecular structures of di-t-butyldichlorosilane and di-t-butylchlorosilane by electron diffraction and molecular mechanics calculations

Abstract The molecular structures of SiBu t 2 Cl 2 and SiBu t 2 ClH in the gas phase have been determined by a combination of electron diffraction and molecular mechanics. The advantage of using molecular mechanics as a guide to the structures is shown. In both structures the butyl groups adopt nearly staggered conformations with respect to opposite SiC bonds. In SiBu t 2 Cl 2 , assuming C 2 symmetry, the parameters ( r a ) are: r (SiCl)=206.9(1), r (SiC)=189.1(4), r [C(1)–C(2)]=154.8(2), r (CH)=113.5(2) pm, ∠ SiC(1)C(2)=108.7(2), ∠ CCH=112.6(9), ∠ CSiC=125.3(6), ∠ ClSiCl=102.7(5), o[C(14)SiC(1)C(2)]=167.1(1), o[SiC(1)C(2)H(3)]=145.9(18)°. In SiBu t 2 ClH, the geometric parameters are: r (SiCl)=208.7(2), r (SiC)=190.3(4), r [C(1)–C(2)]=154.1(1), r (CH)=113.1(3), r (SiH)=148.7 pm, ∠ SiC(1)C(2)=106.5(2), ∠ CCH=113.2(11), ∠ CSiC=125.2(5), ∠ ClSiH= 102.7(13), o[C(14)SiC(1)C(2)]=167.8(8), o[SiC(1)C(2)H(3)]=157.4(17)°.

Determination of the gas-phase molecular structure of bis(trimethylsilyl)sulphide by electron diffraction and molecular mechanics calculations

Abstract The molecular structure of S(SiMe3)2 in the gas phase has been determined by electron diffraction, aided by molecular mechanics (MM2) calculations. The results of two refinements are reported. In the first, the SiMe3 groups were assumed to have local C3 symmetry, while in the second all the SSi distances, SiC distances, and SSiC and CSiC angles were allowed to differ from one another, with the differences fixed at the values calculated by molecular mechanics. Allowing for the asymmetry of the SiMe3 groups had a significant effect on some of the refined parameters, most notably the mean SSiC angle, which increased from 105.6(7) to 109.2(3)°, and the angle SiSSi, which increased from 104.0(5)° to 105.8(7)°. Other major parameters (ra) obtained in the refinement with asymmetric SiMe3 groups are r(SiS)=215.4(1) pm and r(SiC) (mean)=187.1(1) pm. The two SiMe3 groups are twisted by 17.1(13) and 29.6(14)° from the position in which one SiC bond of each group lies anti with respect to the further SSi bond.

Self-assembly of polyoxometalate conjugates: novel models for catalytic surfaces from crystal data

Self-assembly of new organic conjugates of the pentamolybdodiphosphonato cage with cyclic aminomethylphosphonates has been achieved. The crystal structures of two of the conjugates have been determined and all of them characterised by IR spectroscopy. Intramolecular hydrogen bonding of the aminomethyl moiety to cage oxygen and close intermolecular C–H ⋯ O–Mo contacts (between 2.3 and 2.5 A for the H ⋯ O distance) are observed, providing a new model for the interaction of substrates with a polyoxometalate catalytic surface. A scheme for modelling the pentamolybdodiphosphonato cage with a distance-restraint-based model is presented.

Determination of the molecular structure of ethylphosphonothioic dichloride by gas-phase electron diffraction and ab initio calculations

Abstract The molecular structure of ethylphosphonothioic dichloride, CH 3 CH 2 P (S)Cl 2 , in the gas phase has been determined from an electron diffraction study. The gas consists of an equilibrium mixture of two conformers, in which the methyl group is trans or gauche with respect to the sulfur atom, but it is not possible to measure the proportions of the two forms because of the similarity of the sulfur and chlorine scattering powers, and of the PS and PCl bond lengths. Ab initio calculations at the 3-21G* level, were therefore performed, and these indicate that the conformation should be 82% gauche and 18% trans . These proportions were then used in the electron diffraction refinements, and the calculated differences between geometric parameters, most notably in the PCC angles, are also incorporated. Refined parameters ( r a ) for the major conformer include r (PCl) 203.0(1), r (PS) 189. ∠ClPC (mean) 103.1 (5), ∠CPS 116.1 (12) and ∠ClPCl 102.0(4)°.

Determination of the molecular structure of tert- butyldimethylsilane in the gas phase by electron diffraction

Abstract The molecular structure and conformation of SiHBu t Me 2 in the gas phase have been determined by electron diffraction. Assuming local C 3 symmetry within tert -butyl and methyl groups the principal refined parameters are r [SiC(Bu)] 188.6(2), r [SiC(Me)] 188.2(2), r (CC) 154.6(1) pm, ∠CCC 108.5(3), ∠C(Bu)SiC(Me) 111.1(4) and ∠C(Me)SiC(Me) 105.5(10)°. A small steric effect is apparent, with the threefold axis of the tert -butyl group tilted 3.6(10)° away from the Si—methyl groups, so that the three SiCC angles are 114.1 (9), 109.0(6) and 108.3(8)°. The conformation adopted about the SiC (butyl) bond is almost fully staggered with the HSiCC dihedral angle 174.3 (48)°.

Macrocyclic thioether design by molecular modelling

Abstract Two trithiamacrocycles have been designed by molecular modelling to have preorganised endodentate sulfur donor atoms. These new macrocycles have five- and six-membered saturated heterocycles inserted into 2,5,8-trithia[9]-m-benzenophane; molecular dynamics simulations suggest that the endo forms will be rigid on a nanosecond timescale. Optimum metal-sulfur distances which the new ligands will accommodate lie between 2.76 A and 2.95 A, suggesting they will be particularly suitable for a large soft metal ion such as silver(I).