Christian W. Lehmann

(N-methylthiocarbamoyl )tetrathiafulvalene derivatives and their radical cations : synthetic and X-ray structural studies

Lithiation of 4,5-bis(methylsulfanyl)-TTF 9, 4,5-(ethylenedisulfanyl)-TTF 10, 4,5-dimethyl-TTF 11 and 4,5,5′-trimethyl-TTF 12 (TTF=tetrathiafulvalene) followed by reaction with methyl isothiocyanate affords the corresponding (N-methylthio-carbamoyl)-TTF derivatives 14–17, respectively, in 54–70% yields. These new TTF derivatives display a broad intramolecular charge-transfer band in their UV–VIS spectra arising from conjugation between the donor TTF ring and the acceptor N-methylthiocarbamoyl moiety. Steric hindrance between the adjacent N-methylthiocarbamoyl and methyl substituents in 17 causes a marked hyposchromic shift in this band (λmax 395 nm) compared to compounds 14–16 (lambda;max 435–467 nm). Consistent with the electron-withdrawing properties of the N-methylthiocarbamoyl substituent, its attachment to the TTF ring raises slightly the oxidation potential of the system. Charge transfer complexes of these donors and (N-methylthiocarbamoyl)-TTF 2 with 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and salts with bromide anions are reported, some of which have high room temperature conductivity values. The X-ray crystal structures are presented for 16, 17 and the salts 2·Br, 14·TCNQ and (17)2·20. The structure of 16 comprises orthogonal dimers (kappa packing) while in the structure of 17 individual molecules are orthogonal to each other. There is weak intermolecular hydrogen bonding in both 16 and 17. In the structure of 2·Br, the radical cations 2+· are almost planar and they form an infinite stair-like stack of dimers, with bromide anions situated between the stacks, and linked with the cation by a strong N–H‥Br bond. The structure of 14·TCNQ comprises mixed ‥DDAADD‥ stacks; the N-methylthiocarbamoyl group engages in an interstack N–H‥N bond with a TCNQ anion. Analysis of the bond lengths in the structure suggests that there is partial charge transfer from 14 to TCNQ. In the structure of (17)2·20 molecules form mixed ‥DDADDA‥ stacks and analysis of bond lengths suggests that there is only a small degree of charge transfer from donor to acceptor. The geometries of compounds 2, 14, 16, 17 were optimised using the PM3 semi-empirical method and the results compare favourably with the X-ray structural data.

The Fddd four-circle diffractometer for single-crystal X-ray studies at temperatures down to 9 K

The Fddd four-circle diffractometer system has been developed to perform X-ray diffraction experiments at temperatures as low as 9u2005K. The diffractometer consists of: (i) a Siemens rotating-anode generator; (ii) a Huber goniometer with offset X circle; (iii) a Siemens Fast Scintillation Detector; and (iv) an APD `202 Displex cryogenic refrigerator. The belt-driven rotating anode gives an X-ray flux that is far in excess of that obtained from a sealed X-ray tube and leads to faster data collections and the opportunity to study smaller samples. X-ray beam alignment requires precise movements of the 300u2005kg goniometer and this is achieved using compressed air pads. Steel-braided gas lines that allow the transfer of helium gas between the Displex and the compressor are supported by a counterbalance system. The stress on these lines has been reduced by attaching them to the Displex via high-pressure rotating joints and by passing them through a metal ring that is attached to the χ circle. A compact vacuum gauge has been mounted through one of the four ports on the top of the cryostat and gives valuable information on the pressure within the Displex sample chamber during an experiment. Crystals are mounted on sharpened 0.3u2005mm graphite pencil leads that are held in a newly designed sample mount. The temperature reported from the second stage of the Displex has been assessed by consideration of temperature standards that include the solid-state phase transitions of benzil (1,2-diphenylethanedione) and terbium vanadate.

η1- and η2-benzene coordination in [Ag(C6D6)3BF4]

Abstract The title complex with one η2 and two η1 deuterobenzene and one monodentate BF4 ligands was isolated as a by-product in the reaction between [(dppe)RhCl]2 and EtCl in C6D6, in the presence of AgBF4 and its X-ray crystal structure determined.

Low temperature neutron and X-ray diffraction study of imino(triphenyl)phosphorane

The structure of imino(triphenyl)phosphorane, Ph 3 PNH 1 has been determined by low-temperature X-ray and neutron diffraction. This dual study is the first such for an iminophosphorane. From the neutron diffraction data, the P-N bond length is 1.582(2) A and the P-N-H angle is 115.0(2)°.

New tetrathiafulvalene derivatives bearing thioamide substituents

The synthesis of compounds 2b-e are described. The single crystal X-ray structures of compounds 2b and 2c are reported.

Half-sandwich imido complexes of niobium bearing alkyne, benzyne and benzylidene ligands: relatives of the zirconocene family

Reactions of [Nb(C5H5)(NC6H3Pri2-2,6)Cl2] 1a and [Nb(C5Me5)(NC6H3Pri2-2,6)Cl2] 1b with 1 and 2 equivalents of benzylpotassium respectively gave the niobium benzyl derivatives [Nb(C5H5)(NC6H3Pri2-2,6)Cl(CH2Ph)] 2 and [Nb(C5Me5)(NC6H3Pri2-2,6)(CH2Ph)2] 3. Treatment of 3 with trimethylphosphine afforded the benzylidene complex [Nb(C5Me5)(NC6H3Pri2-2,6)(PMe3)(CHPh)] 4. Complex 1a reacted with phenylmagnesium chloride in the presence of PMe3 to give [Nb(C5H5)(NC6H3Pri2-2,6)Ph2(PMe3)] 5 which upon heating at 70xa0°C in heptane, converts to the η2-benzyne complex [Nb(C5H5)(NC6H3Pri2-2,6)(η2-C6H4)(PMe3)] 6. The niobium(III) complexes [Nb(C5H5)(NC6H4But-2)(PMe3)2] 8a and [Nb(C5Me5)(NC6H3Pri2-2,6)(PMe3)2] 8b were obtained upon magnesium reduction of 1a and 1b respectively in the presence of an excess of PMe3. They were converted into [Nb(C5H5)(NC6H4But-2)(η2-R1CCR2)(PMe3) (R1xa0=xa0R2xa0=xa0Ph 9a; R1xa0=xa0Ph, R2xa0=xa0H 9b) and [Nb(C5Me5)(NC6H3Pri2-2,6)(η2-PhCCPh)(PMe3)] 9c upon treatment with the appropriate alkyne. The molecular structures of the 2-tert-butylimido complexes [Nb(C5H5)(NC6H4But-2)Cl2] 7 and 9a have been determined.

Synthesis and X-ray structures of tetralithium derivatives oftert-butylcalix[4]arene containing unique Li–O cores basedon a square-pyramidal geometry

Tetralithiation of tert-butylcalix[4]arene in the presence of nhmpa (hexamethylphosphoramide) results in the isolation of either a nmonomeric complex in which LiOH is incorporated into an nLi n 5 nO n 5 n core based on an isolated square pyramid of Li natoms, or a dimeric LiOH-free species containing an nLi n 8 nO n 8 n core in which the same structural motif is nmaintained by edge-sharing of two square pyramids of Li atoms.