Rhenium anions

Paramagnetic rhenium anions of the composition [Re(NO)X5] have been known for 30 years. 

Force-constant (F) calculations for the dimeric rhenium anion Re2Br were performed using both a valence force field and a Urey-Bradley force field (30). Neither analysis was considered entirely satisfactory by the authors, but both treatments led to very similar values for FReBr of 1.63 0.02 mdyne A"1. Of more interest with regard to the strength of the quadruple bond is the fact that the results of both calculations suggested that FReRe lies somewhere in the... 

F. A. Cotton s Centenary Lecture Quadruple Bonds and other Multiple Metal to Metal Bonds , Chem. Soc. Rev. 4, 27-53 (1975) (The detailed story of elucidating the structure of the rhenium anions is given). 

Perfluorobutadiene readily reacts with anions such as 7r-C5H5Fe(CO)2 and Re(CO)s- forming cis- or tranj-perfluorobutadienyl complexes, M—CF—CF—CF—CF2, respectively, and with hexafluorobut-2-yne the rhenium anion Re(CO)5 forms the only known allenyl derivative (CO)sReCCF3=C=CF2 [226a]. 

In earlier procedures, the ReO anion was precipitated from water as the relatively insoluble potassium salt. Reduction of KReO with hydrogen gas gives rhenium metal, but the metal is contaminated with ca 0.4 wt % potassium that cannot be separated easily. Although suitable for some purposes, rhenium formed from KReO is found to be unsatisfactory in appHcations such as those for use in filaments in mass spectrometer systems. The route involving NH ReO avoids this problem. 

Salts of perrhenic acid may be obtained in acid—base reactions, and may include the tetrahedral ReO anion or the octahedral anion ReO , eg, in Ba (ReOg)2 [13598-09-9], Ammonium perrhenate and perrhenic acid, as well as rhenium metal, are sold by the primary suppHers of this element. 

Again, fluoro and oxo complexes of rhenium predominate. The reaction of KF and ReFe in an inert PTFE vessel yields pink K2[ReFs], the anion of which has a square-prismatic structure hydrolysis converts it to K[ReOFs]. 

The potentially versatile ligating ability of trisimidometaphosphate anions is manifested in the formation of either dispirocyclic (13) or heterocubane (14) rhenium complexes from the reaction of [(Me3Si)2NP(=NSiMe3)2] with RefCOljCl [18, 19]. Both (13) and (14) contain the dianionic [(RN)2P(fi-NR)2P(NR)2] "... 

Non-ionic thiourea derivatives have been used as ligands for metal complexes [63,64] as well as anionic thioureas and, in both cases, coordination in metal clusters has also been described [65,66]. Examples of mononuclear complexes of simple alkyl- or aryl-substituted thiourea monoanions, containing N,S-chelating ligands (Scheme 11), have been reported for rhodium(III) [67,68], iridium and many other transition metals, such as chromium(III), technetium(III), rhenium(V), aluminium, ruthenium, osmium, platinum [69] and palladium [70]. Many complexes with N,S-chelating monothioureas were prepared with two triphenylphosphines as substituents. 

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). 

Koide et al. [537] have described a graphite furnace atomic absorption method for the determination of rhenium at picomolar levels in seawater and parts-per-billion levels in marine sediments, based upon the isolation of heptavalent rhenium species upon anion exchange resins. All steps are followed with 186-rhenium as a yield tracer. A crucial part of the procedure is the separation of rhenium from molybdenum, which significantly interferes with the graphite furnace detection when the Mo Re ratio is 2 or greater. The separation is accomplished through an extraction of tetraphenylarsonium perrhenate into chloroform, in which the molybdenum remains in the aqueous phase. 

Rhenium Adsorption on Deacidite FF anion exchange resin, elution Neutron activation analysis 0.06 ng/1 [539]... 

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