Rhenium compounds anions

Raman spectra of quadruply bound molybdenum dimers show a much greater frequency variation for the metal- metal stretching mode than is found in related rhenium compounds. The Mo2X - anions and other halo derivatives are considered first, then a review of tetracarboxylatodimolybdenum vibrational data is given, and finally comparisons for various molybdenum dimers are presented. 

We discuss here two examples of vibronic effects in polynuclear highly symmetrical transition metal clusters. The existence of degenerate and quasi-degenerate molecular orbitals in their energy spectra results in the Jahn-Teller effect or in the vibronic mixing of different electronic states. We show that both quantum-chemical methods and model approaches can provide valuable information about these vibronic effects. In the case of the hexanuclear rhenium tri-anion, the Jahn-Teller effect is responsible for the experimentally observed tetragonal distortion of the cluster. The vibronic model of mixed-valence compounds allows to explain the nature of a transient in the photo-catalytic reaction of the decatungstate cluster. 

Salts of the perrhenate anion (including perrhenic acid) are not only the single most important group of starting materials for the synthesis of other rhenium compounds but are also of importance in catalysis and other commercial processes. Although they are formally coordination complexes of Revn and they appear quite extensively in the chemical literature (e.g. see Chemical Abstracts), much of the interest in them is outside the confines of the topic of coordination chemistry as it is commonly accepted. Accordingly, an effort has been made here to keep the coverage of their chemistry to a minimum. 

About 400 compounds containing the T12-H2 ligand have been made that are stable. Almost all of them are octahedral with the metal in the d electron configuration, from Cr(0) to W(0) across the periodic table to Rh(lll) and Ir(III). There are a few dihydrogen complexes known with metals in other oxidation states. These are relatively rare. There are seven coordinate rhenium compounds like [Re(H2)(H)2(CO)(PMe2Ph)3]+ [8] and very unstable d systems like [Pt(ll2-H2)(PR3)2H]+ [9]. Neutral and cationic complexes are known but not anionic ones. Presumably anionic dihydrogen complexes are unstable because the metal s dTC electron richness promotes the oxidative cleavage of the H-H bond by d7t(M) —> o (H2) donation. 

In the case of the rhenium aqua-ion [Re(OH2)3(CO)3]+ (33b) the question has been posed whether complex-anion can be considered to be a Bronsted acid. Titrations with hydroxide in water yielded a pKa value of 7.55 which is exceptionally low for a +1 cation. After the deprotonation of one coordinated water molecule, polymer formation over (/r-OH) bridges was initiated and the two compounds [Re3(/T3-OH)(/T-OH)3(CO)9r (35) and [Re2(/i-OH)3(CO)6] were (36) isolated and structurally characterized (Scheme 6). 

ReOCU reacts with PhNCO to give the rhenium(VI) compound [Re(NPh)Cl4] which forms adducts with donor solvents such as TFIF or acetonitrile. Anionic [Re(NPti)Cl5] is obtained when [Re(NPh)Cl4] is treated with [Mc4N]Cl. Two other approaches to rhenium(VI) arylimido compounds include an azo splitting reaction starting from 2-(arylazo)pyridines and the oxidation of rhenium(V) imides by nitric acid. ... 

Compared with the huge number of oxo complexes only a few rhenium(V) compound with terminal sulfldo complexes are known. The square-pyramidal complex anion [ReS(S4)2] was first isolated in pure form in 1986 by a reaction of Rc207 with (Ph4P)Br and ammonium polysulfide in acetonitrile and the structure of the Ph4P+ salt has been elucidated. Later, the same complex anion was prepared from starting materials such as [Re2Cl8] , perrhenate, ... 

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