Density functional description of the bonding in the m3-chalcogenido hexanuclear octahedral clusters [Co6(m3-X)8(Pet3)6 ] (X=S, Se, Te)

Density functional theory (DFT) in the local density approximation has been applied to describe the bonding in the μ3-chalcogenido hexanuclear cobalt clusters of formula [Co6(μ3-X)8(PR3)6] (X = S, Se, Te). The geometries of the clusters have been optimised and the bonding interactions in the sulfide derivative have been analysed using a fragment decomposition scheme. Direct metal-metal interactions are negligible. The electrochemical behaviour reported for the sulfide cluster has been rationalised

Dinuclear ruthenium bipyridine complexes with a bis(iminodioxolene)-meta-phenylene ligand: magnetic coupling and mixed valence character of the semiquinonato species

The dinuclear bis-iminosemiquinonato [Ru(bpy)2(L)2Ru(bpy)2](PF6)2 complex where L is the deprotonated form of N,N′-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-1,3-phenylenediamine (H4L), has been synthesised. For comparison purposes, the mononuclear iminosemiquinonato [Ru(bpy)2L′]PF6 formed by the N-phenyl-o-aminophenol (H2L′) was also investigated. Magnetic investigation evidences that the bis-semiquinonato species is characterised by a moderately strong ferromagnetic interaction (H = JS1·S2, J = −85(5) cm−1). This result is the theoretically expected one and it is contrasting with the antiferromagnetic interaction observed in previously investigated complexes containing the same ligand. It is suggested that the different behaviour is determined by the different coordination requirements occurring in these complexes. The spectroelectrochemical analysis provides a clear evidence of the valence trapped character of the mono-semiquinonato forms of the ligand. The two mixed valence semiquinonato species containing the quinonato-semiquinonato and semiquinonato-catecholato bridging ligand can be described as class II, but show a significantly different electronic coupling. The electronic factors determining this behaviour are discussed

Structure and magnetism of Nickel(II) and Manganese(II) complexes of a nytronyl nitroxide carboxylic acid

The organic anionic radical 2-(4-carboxy-phenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl-3-oxide (NITpBA−) has two different types of potentially metal-coordinating sites. One is the carboxylate group, the other consists of the two oxygen atoms belonging to the nitronyl nitroxide part. The nitronyl nitroxides have generally revealed a rather weak coordinating ability and they have been found only to coordinate metal ions with a low electron density as in the case of hexafluoro-acetylecetonates. Howeverm, in the simple, carboxylate salt Mn(NITpBA)2(H2O)2, each MnII ion is coordinated simultaneously by water, carboxylate oxygens and radical oxygens with the NITpBA− ligands bridging the MnII ions such as to obtain a ladder-like structure. The NiII derivative has also been prepared and it was found to be isostructural with the Mn salt. Mn(NITpBA)2(H2O)2 crystallizes in the monoclinic system, P21/c (No. 14) space group, a = 12.644(2), b = 9.203(2), c = 13.598(2), β = 115.21 (1)°, V = 1431.6(4) Å3, Z = 2, refinement with 2150 reflections, 196 parameters, yielded R = 0.046 and Rw = 0.051. The magnetic susceptibility as a function of temperature of these compounds is readily accounted for on the basis of their structure. A chain model was adopted to reproduce the observed magnetic susceptibility of the NITpBAH free radical

The redox behaviour of ferrocene derivatives XIII. Fluorenyl ferrocenes

The electrochemical behaviour of a series of 2,7-substituted-9-fluorenyl-ferrocenes has been studied. Irrespective of the inductive effects played by the different substituents of the fluorenyl fragment, all of them undergo a chemically reversible one-electron removal at almost coincident potential values. Upon exhaustive oxidation, the original red complexes turn orange–brown and the oxidised solution is EPR silent at liquid nitrogen temperature. Mass spectrometry confirms that the electrogenerated cations maintain the original molecular frame. In order to account for the fact that the constancy in redox potentials and the EPR inactivity at 77 K of the oxidised species, both of which prelude an iron-centred oxidation, conflict with the orange colour of the oxidation products (instead of the usual blue-to-green colour of ferricinium species), which preludes a ligand-centred oxidation, a theoretical EHMO analysis was performed. In spite of some uncertainty bound to the energy scale of the MO ordering, a metal-centred oxidation seems favoured over a ligand-centred process

Oligonuclear ferrocenolato and 1,1 '-ferrocenediolato derivatives of phosphorus: synthesis, structure and electrochemical behaviour

Starting from 1,1′-ferrocenediol, fc(OH)2, several 1,3-dioxa-2-phospha-[3]ferrocenophanes such as [fcO2]P(O)R (R = Cl (1), Ph (2), Fc (3), OFc (4)) and fc(OP[O2fc])2 (5) were synthesized, and both tri(ferrocenyl)phosphite and tri(ferrocenyl)phosphate, P(OFc)3 (6) and P(O)(OFc)3 (7), were obtained starting from ferrocenol, Fc-OH. The new complexes 1–7 were characterized by a consistent set of 1H, 13C and 31P NMR spectroscopic data, and the molecular geometry of 7 was determined by an X-ray crystal structure determination. Electrochemical studies indicate that 3 and 4 are oxidized in two consecutive steps; the formation of the monocations, [3]+ and [4]+, is reversible, and the dication [4]2+ is quite stable. The trimetallic compounds 5–7 undergo two nearly overlapping anodic processes to give the corresponding trications

Synthetic and electrochemical studies of some metal complexes of 1,3,5-triethynylbenzene

A series of compounds featuring metallic fragments around the periphery of a 1,3,5-triethynylbenzene core have been synthesized. By using several synthetic methods, metallic units such as cis-[RuCl2(dppm)2], cis-[OsCl2(dppm)2] and [RuCl(η-C5H5)(PPh3)2] have been treated with the aromatic acetylide ligand to introduce one, two or three metallic centres. Electrochemical studies showed that the bimetallic trans-[HC[triple bond, length half m-dash]CC6H3{C[triple bond, length half m-dash]CRuCl(dppm)2}2] and trans-[HC[triple bond, length half m-dash]CC6H3{C[triple bond, length half m-dash]COsCl(dppm)2}2] species undergo two separated one-electron oxidations thus indicating that the central triethynylbenzene unit allows communication between the two peripheral metal subunits. The compounds [(HC[triple bond, length half m-dash]C)2C6H3C[triple bond, length half m-dash]CRu(η-C5H5)(PPh3)2], [HC[triple bond, length half m-dash]CC6H3{C[triple bond, length half m-dash]CRu(η-C5H5)(PPh3)2}2] and [C6H3{C[triple bond, length half m-dash]CRu(η-C5H5)(PPh3)2}3] each show separated one-electron oxidations (though these are less reversible than for the previous compounds mentioned) again demonstrating the electronic communication amongst the peripheral metal centres through the organic linkage. Chemical oxidation has been carried out on the [Ru(η-C5H5)(PPh3)2]-containing species affording mixed-valence species consistent with those produced by successive electrochemical oxidation

4-Ethynylpyridine as a bridging moiety in mixed Rh/Re complexes

A paramagnetic, dimeric RhIIIRhII complex of the formula [Rh2(form)4(C≡CC5H4N)] (1) [form = N,N′-di-p-tolylformamidinate; C5H4N = pyridyl (py)] has been synthesized and used as starting material to prepare heterotrimetallic complexes of composition [Rh2(form)4(C≡Cpy){Re(CO)3(bipy)}][OS(=O)2CF3] (2) and [Rh2(form)4(C≡Cpy){Re(CO)3(tbu2bipy)}][OS(=O)2CF3] (3). These complexes have been examined by vibrational spectroscopy, EPR spectroscopy, thermogravimetry and cyclic voltammetry. They are heat-stable and can be handled in air without problems. The observed interactions between the Rh2 and the Re subunits, however, are weak, and a significant charge transfer does not seem to take place

A re-examination of the reaction between 1,1 '-bis(diphenylphosphino)ferrocene (dppf) diselenide and [Ru-3(CO)(12)]. Electrochemical behaviour of the isomeric Nido-clusters [Ru-3(mu(3)-Se)(2)(dppf)(CO)(7)] and [Ru-3(mu(3)-Se)(2)(mu-dppf)(CO)(7)] and crystal structure of [Ru3Se{mu-P(Ph)C5H4FeC5H4PPh2}(mu-OCPh)(CO)(6)]

The reactions of 1,1'-bis(diphenylphosphino)ferrocene diselenide (dppfSe2) with [Ru-3(CO)(12)] at 60 and 110 degreesC afford, respectively, the two isomeric nido-clusters [Ru-3(mu (3)-Se)(2)(dppf)(CO)(7)] (2) and [Ru-3(mu (3)-Se)(2)(CO)(7)(mu -dppf)] (3) which contain dppf as chelating and bridging ligand, respectively. The chelated derivative 2, attainable under kinetic control, can be converted to the more stable bridged cluster 3 by thermal treatment in toluene solution. Moreover the cluster [R mu Se-3{mu -P(Ph)C5H4FeC5H4PPh2}(mu -OCPh)(CO)(6)] (4) was isolated as a minor product. Its cluster core consists of a metal triangle capped by a selenium atom and bridged on two sides, respectively, by a phosphido ligand and by a benzoyl group both deriving from multiple fragmentation of dppf diselenide and migratory insertion of a Ph ring into a CO ligand. Isomers 2 and 3 present different electrochemical behaviour, the bridged one giving a more complicated voltammetric pattern