Trevor R. Spalding

Novel rhodathiaborane complexes derived from [(PPh3)2RhSB9H10]

The compound [8,8-(PPh3)2-8,7-RhSB9H10], (1), has a formal closo electron count but a nido structure, exhibits unusual fluxional behaviour in solution and reacts to give both closo and nido compounds, e.g., closo-[2,3-(PPh3)2-3-(Cl)-µ-2; 3-(Cl)-2-(Ph2P[graphic omitted]H8], (2), and nido-[8,8-(PPh3)2-µ-8;9-(S2CH)-8,7-RhSB9H9], (3); the structures of (1), (2), and (3) were determined by X-ray crystallographic methods.

Sterically-induced low temperatur polyhedral rearrangements of carbaplatinaboranes: Synthesis and crystal structures of 1-Ph-3,3-(PMe2Ph)2-3,1,2-PtC2B9H10, 1-Ph-3,3-(PMe2Ph)2-3,1,11-PtC2B9H10, 11-Ph-3,3-(PMe2Ph)2-3,1,11-PtC2B9H10 and 1,11-Ph2-3,3-(PMe2Ph)2-3,1,11-PtC2B9H9

Abstract Reaction of cis-Pt(PMe2Ph)2Cl2 with Tl2[7-Ph-7,8-nido-C2B9H10] affords 1-Ph-3,3-(PMe2Ph)2-3,1,2-PtC2B9H10, mild thermolysis (55°C) of which yields 1-Ph-3,3-(PMe2Ph)2-3,1,11-PtC2B9H10 and 11-Ph-3,3-(PMe2Ph)2-3,1,11-PtC2B9H10. Both of the latter compounds are produced by the microwave irradiation of a mixture of cis-Pt(PMe2Ph)2Cl2 and [HNMe3][7-Ph-7,8-nido-C2B9H11]. When cis-Pt(PMe2Ph)2Cl2 is allowed to react with Tl2[7,8-Ph2-7,8-nido-C2B9H9] at room temperature the only isolable species is 1,11-Ph2-3,3-(PMe2Ph)2-3,1,11-PtC2B9H9. The generation of rearranged products with 3,1,11-PtC2B9 architectures is inconsistent with a diamond-square-diamond mechanism for the isomerisation of icosahedral heteroboranes.

Analysis of Nanocrystalline ZnS Thin Films by XPS

Nanocrystalline ZnS thin films were synthesized by chemical vapor deposition (CVD) using Zn(O-iPrXan)2 [O-iPrXan =S2COCH(CH3)2] as a single-source precursor compound. The coatings were deposited on silica substrates in N2 atmosphere at temperatures between 200 and 450 °C and subsequently characterized by glancing-incidence x-ray diffraction (GIXRD), secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM), UV-Vis absorption spectroscopy, x-ray photoelectron (XPS), and x-ray excited auger electron (XE-AES) spectroscopies. This work is dedicated to the XPS and XE-AES characterization of a representative zinc sulfide thin film. Besides the wide scan spectrum, detailed spectra for the Zn 2p3/2, Zn 3p, Zn LMM, S 2p,O 1 s, and C 1s regions and related data are presented and discussed. Both the S/Zn atomic ratio and the evaluation of the Auger parameter point out to the formation of stoichiometric zinc sulfide. Moreover, oxygen and carbon contamination were merely limited to the outermost sample layers.

Metallaheteroborane chemistry: Part 14. Synthesis of the {MS2B7}-cluster compounds [9,9-(PX3)2-9,6,8-PtS2B7H7] (where X=Ph or OMe), [9,9-(PPh3)2-9,6,8-RhS2B7H8] and [5,5-(PPh3)2-5,6,10-RhS2B7H8], and the {M2S2B7}-cluster compound [(PPh3)2HRh(PPh3)ClRhS2B7H7]

Abstract The ten-vertex {MS 2 B 7 } cluster compounds [9,9-(PPh 3 ) 2 -9,6,8-PtS 2 B 7 H 7 ] 1a , [9,9-{P(OMe) 3 } 2 -9,6,8-PtS 2 B 7 H 7 ] 1c , and [9,9-(PPh 3 ) 2 -9,6,8-RhS 2 B 7 H 8 ] 2 were synthesised in reactions between arachno -4,6-S 2 B 7 H 9 and the metal phosphine complexes [Pt(PPh 3 ) 4 ], [PtCl 2 {P(OMe) 3 } 2 ] and [RhCl(PPh 3 ) 3 ], respectively. Heating a solution of [9,9-(PPh 3 ) 2 -9,6,8-RhS 2 B 7 H 8 ] in benzene afforded its isomer [5,5-(PPh 3 ) 2 -5,6,10-RhS 2 B 7 H 8 ] 3 . The eleven-vertex {M 2 S 2 B 7 } cluster compound, [(PPh 3 ) 2 HRh(PPh 3 )ClRhS 2 B 7 H 7 ] 4 was synthesised in the reaction between S 2 B 7 H 9 and [RhCl(PPh 3 ) 3 ] in 1:2 molar ratio, and exhibits a novel cluster structure with the metal and sulphur atoms assembled in a sequential M–S–M–S manner on the borane sub-cluster matrix. All compounds 1 to 4 were characterised by spectroscopic methods and, in the cases of 1a and 4 , by single-crystal X-ray diffraction analysis. These observations are discussed in the light of the electronic and structural requirements of the metal units involved in metallathiaborane cluster compounds.

The formation of dimensionally ordered germanium nanowires within mesoporous silica

Herein is described a supercritical fluid solution-phase method for the synthesis of high aspect ratio nanowires of true nanometre diameter within the pores of an ordered mesoporous material. Using powder X-ray diffraction (PXRD), 29Si MAS–NMR and transmission electron microscopy (TEM), it is possible to show that the quantum confined nanowires formed partially fill the pores of the mesoporous solid and are orientated so that the 〈100〉 plane of the wires runs parallel to the pore direction. We also show that the wires have an expected diamond-like structure although there is a measurable lattice expansion compared to bulk forms of germanium.

A Gaussian 80 (6-21G) study of the species SiHn (n = 1–4) and SiHm+(m = 1–5): Some comments on the electron impact mass spectrum of silane

Abstract Gaussian 80 (6-21G) calculations were performed in both HF and CI modes on the species SiHn (n = 1–4) and SiHm+ (m = 1–5). In general the agreement between calculated and experimentally determined properties such as the structures of SiHn molecules and the ionisation potentials of SiH4 were very good. The present results were compared with those previously published. The production of the ions SiH3+ and SiH2+ in the electron impact mass spectrum of silane was also analysed.

The redox behaviour of the cluster anion [Fe4N(CO)12]−. Electron transfer chain catalytic substitution reactions. Crystal structure of [Fe4N(CO)11PPh3)]−

Abstract The electrochemical investigation of the redox properties of the monoanion [Fe4N(CO)12]− points out its ability to undergo sequentially two one-electron reductions. The first step leads to the quite stable dianion [Fe4N(CO)12]:2−; the EPR results indicate that in frozen solution an equilibrium exists between two different molecular geometries of such a dianion. The second electron addition produces the relatively short-lived trianion [Fe4N(CO)12]3−. In the presence of monodentate phosphines, the redox change [Fe4N(CO)12]−/2− triggers the electrocatalytic substitution of one CO group to afford the substituted monoanions [Fe4N(CO)11(PR3)]−. As a matter of fact, sub-stoichiometric amounts of Ph2CO − produce [Fe4N(CO)11(PPh3)]−, the crystal structure of which has been solved. Crystal data for [N(PPh3)2][Fe4N(CO)11(PPh3)]: triclinic, space group P 1 (No. 2), a=11.009(6), b=17.285(4), c=17.380(2) A, α=103.11(3), β=91.18(2), γ=105.26(3)°, Z=2, Dc=1.444 g cm−3, Mo Kα radiation (λ=0.71073 A), μ(Mo Kα)=10.5 cm−1, R=0.048 (Rw=0.054) for 5010 independent reflections having I > 3σ(I). Preliminary evidence is given that in the presence of bidentate phosphines one CO ligand substitution occurs at room temperature, whereas two CO groups are replaced at higher temperatures.

Conformational polymorphism and fluxional behaviour of M(PR3)2 units in closo-twelve-atom metallaheteroboranes with MX2B9(X = C or As) and MZB10 cages (Z = S, Se or Te)

The compounds [3,3-(PEt3)2-closo-3,1,2-PtAs2B9H9]1 and [2,2-(PMe2Ph)2-closo-2,1-PtSB10H10]2 were synthesised and characterised by NMR spectroscopy and X-ray crystallography. Crystals of 1 exhibit conformational polymorphism with five conformers of the Pt(PEt3)2 unit above the As2B3 face; those of 2 contain single conformers. The free energy of the barrier to rotation of the Pt(PMe2Ph)2 unit above the SB10 cage ligand in 2 has been determined in chloroform solution and is compared with data from other platinum and palladium metallaheteroboranes containing C2B9H11, As2B9H9, SeB10H10 and TeB10H10 ligands. A mechanism for the rotation of M(PR3)2 units above heteroborane ligand faces is suggested. It involves shifting the M(PR3)2 unit viaηn-bonded species (n < 5) with a concomitant twisting of the M(PR3)2 unit about an axis passing approximately through the metal atom and the antipodal B atom.

Metallaheteroborane chemistry. Part 10. Synthesis and characterisation of closo-structured rhodathiaborane complexes [1-(CO)-1-L-3-L′-1,2-RhSB9H8](L = L′= PPh3; L = PMe2Ph, L′= PMe2Ph or PPh3)

The reaction of CO with [8,8-(PPh3)2-8,7-RhSB9H10]1 in benzene yields [8-(CO)-8,8-(PPh3)2-nido-8,7-RhSB9H10]3 in 98% yield. Refluxing a benzene solution of 3 produces [1-(CO)-1,3-(PPh3)2-closo-1,2-RhSB9H8]4 in 46% yield. The reaction between 4 and excess of PMe2Ph in refluxing benzene affords [1-(CO)-1-(PMe2Ph)-3-L-closo-1,2-RhSB9H8][L = PMe2Ph 5(25%) or PPh36(46%)]. NMR data (1H, 11B and 31P) confirm the nido nature of 3 and the closo structures of compounds 4–6. X-Ray diffraction studies of 4, 4′(=4·1.5C6H5Me), and 5 showed that there was conformational disorder in all three cases. The structure of 5 was solved in space group P21/n with unit cell dimensions of a= 9.626(2), b= 23.714(5), c= 11.595(2)A, β= 109.00(2)°, and Z= 4. The final R factor was 0.027 for 4472 observed reflections. Principal interatomic distances are Rh(1)–S(2) 2.3736(7), Rh(1)–P(1) 2.3090(7), Rh(1)–C(1) 1.855(3), Rh(1)–B(3) 2.101(3), Rh(1)–B (4, 5, 6, 7) 2.380(3)–2.444(3), S(2)–B 1.923(3)–1.989(4), B–B 1.719(4)–1.897(4) and B(3)–P(2) 1.895(3)A. The geometry of the RhSB9 cage in 5 was used as a template in the final refinement of the structures of 4 and 4′ which were more disordered: 4, space group C2/c, a= 37.529(11), b= 10.749(5), c= 19.536(5)A, β= 101.96(2)°, Z= 8, R 0.051 for 3970 observed reflections; 4′, space group P, a= 11.933(2), b= 14.157(2), c= 14.190(2)A, α= 79.25(1), β= 83.27(1), γ= 87.32(1)°, Z= 2, R 0.041 for 6959 observed reflections.

Bonding in clusters. Part 3. Protonation of nido-pentaborane(9), nido-hexaborane(10), and closo-hexaborate(6)(2–)

The bonding and structures of B5H9, B6H10, and B6H62– and the protonated species B5H10+, B6H11+, B6H7–, and B6H8 are analysed with MNDO, Gaussian-80, and self-consistent charge calculations. The known isomer of B6H10 is shown to be more stable than other isomers for which metalloborane analogues are known. The bonding in B5H10+ can be regarded as a B5H8+⋯ H2 complex but B6H11+ prefers a structure with six B–H terminal and five B–H–B bridged bonds. Protonation of B6H62– gives a face-capped B6H7– structure. Diprotonation of B6H62– produces a molecule in which the B6 octahedral skeleton is entirely disrupted and the molecule is predicted to be highly unstable. Attention is drawn to some of the observed differences in the chemistries of related borane, metalloborane, and metallo-clusters.