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Transport properties of (DT-TTF)2[ Cu(mnt)2] show a semiconducting behaviour comparable to the one of the isostructural Au analogue but with a sharp 2ndorder phase transition at Tc=235 K. Under pressure, Tcdecreases and the compound becomes metallic above Tcfor pressures higher than 15 kbar. The X-ray scattering study shows that the transition at Tccorresponds to a dimerisation of the molecules along the stacking direction. Key words.Electrical conductivity – X-ray scattering – Pressure studies – Spin-ladder compounds.

New half-sandwich molybdenum complexes [Mo(CpBz)Cl2(O)] (1), [{Mo(CpBz)(O)2}2(μ-Ο)] (5), and [Mo(CpBz)Cl2]2 (6) (CpBz = C5(CH2Ph)5), the tungsten derivative [W(CpBz)Cl(O)2] (3), and a high yield synthesis of [Mo(CpBz)Cl(O)2] (2) are described. The molecular structures and cyclic voltammetry measurements of 1 and 2 and a comparative study of various molybdenum dioxo complexes as olefin epoxidation catalyst precursors are also presented. The performance of [Mo(CpPrⁱ4)Cl(O)2] (9) as cyclooctene epoxidation catalyst using TBHP as oxidant was determined and compared with other [MoCp‘Cl(O)2] complexes (Cp‘ = C5H5 (7), C5Me5 (8), CpBz (2)) to assess the activity dependence on the ring substituents. Under the same experimental conditions, bimetallic compounds [{MoCp‘(O)2}2(μ-Ο)] (Cp‘ = CpBz (5), Cp* (10), CpBu^t3 (11), CpPrⁱ4 (12)) have been tested and [CpMoO2]2O was checked in aqueous solution, with H2O2 and TBHP as oxidant. Finally, [Mo(CpBz)(CO)3CH3] (4) was used as a catalyst precursor for cyclooctene epoxidation in the presence of TBHP. The analogy between the behaviors displayed by this complex and complex 2 is discussed.

The reactions of [Ti(η⁵-Ind)(NMe2)2Me], [Ti(η⁵-Ind)(NMe2)Cl2], and [Zr(η⁵-Ind)(NMe2)2Cl] with 2,6-dimethylphenyl isocyanide (CN(2,6-Me2Ph)) and tert-butyl isocyanide (CN-t-Bu) have been investigated. For the first complex, insertion occurs exclusively into the Ti−C bond to give [Ti(η⁵-Ind)(NMe2)2{C(Me)&dbd;N-t-Bu}] (1), which, according to DFT results, is due to the weakness of the Ti−CH3 bond when compared to Ti−NR2. [Ti(η⁵-Ind)(NMe2)Cl2] was found to react with 1 equiv of CN(2,6-Me2Ph) to yield [Ti(η⁵-Ind){C(NMe2)&dbd;N(2,6-Me2Ph)}Cl2] (2). Two equivalents of 2,6-dimethylphenyl isocyanide reacts with [Zr(η⁵-Ind)(NMe2)2Cl] to give the double insertion compound [Zr(η⁵-Ind){C(NMe2)&dbd;N(2,6-Me2Ph)}2Cl] (3). The same reaction performed with CN-t-Bu proceeds slowly and enabled the characterization, by NMR, of [Zr(η⁵-Ind)(NMe2){C(NMe2)&dbd;N-t-Bu}Cl] (4) and [Zr(η⁵-Ind){C(NMe2)&dbd;N-t-Bu}2Cl] (5). The molecular structures of 2 and 3 have been determined by X-ray diffraction. DFT calculations of the insertion of CNH in the zirconium nitrogen bonds of [Zr(η⁵-Ind)(NR2)2Cl] (R = H, Me) have been performed and show that the progressive stability of the insertion products accounts for the experimentally found double insertion product.

A series of new acetylide complexes of the type [Fe(η⁵-C5H5)(P&arcraise;P)(p-C&tbd1;CC6H4R)] (P&arcraise;P = DPPE (=1,2-bis(diphenylphosphino)ethane), (R)-PROPHOS (=(R)-(+)-1,2-bis(diphenylphosphino)propane), R = NO2, C6H4NO2, (Z)-C(H)&dbd;C(H)C6H4NO2, (E)-C(H)&dbd;C(H)C6H4NO2) have been synthesized by halide abstraction from the precursors [Fe(η⁵-C5H5)(P&arcraise;P)(I)] and fully characterized. Quadratic hyperpolarizabilities (β) for the complexes have been determined by hyper-Rayleigh scattering at 1064 nm. The influence on the nonlinear response of acetylide chain length in proceeding from 4-nitrophenylethynyl to 4-nitrobiphenylethynyl and 4-nitro-(E)-stibenylethynyl has been studied, revealing values of the first hyperpolarizabilities among the highest reported for organometallic molecular materials. Comparisons on the nonlinear efficiencies are drawn with the related well-known families of compounds [Ru(η⁵-C5H5)(PR3)2(p-C&tbd1;C−(aryl)−NO2)] and [Fe(η⁵-C5H5)(P&arcraise;P)(p-N&tbd1;C−(aryl)−NO2)]⁺. Cubic hyperpolarizabilities (γ) determined by Z-scan at 800 nm are consistent with an increase in γ upon replacing Ru by the more easily oxidizable Fe and upon chain-lengthening the delocalizable π-bridging unit (proceeding from 4-C6H4 to (E)-4,4‘-C6H4CH&dbd;CHC6H4). X-ray crystallographic structures of complexes [Fe(η⁵-C5H5)(DPPE)(p-C&tbd1;CC6H4NO2)] and [Fe(η⁵-C5H5)(DPPE)((E)-p-C&tbd1;CC6H4C(H)&dbd;C(H)C6H4NO2)] were studied in order to investigate the existence of π-back-donation suggested by spectroscopic and electrochemical data. Crystal packing was analyzed with the aim of assessing the alignment of the molecules in the lattice and hence suggesting the magnitude of NLO properties at the macroscopic level.