Mukul C. Chakravorti

Electrosynthesis of coordination compounds by the dissolution of sacrificial metal anodes

Abstract The article reviews the electrosynthesis of different kinds of coordination compound by the dissolution of sacrificial metal anodes into aqueous and non-aqueous media. The advantages of the method have been emphasized and a brief discussion on the mechanism has been included. The coverage of the literature is almost complete up to 1992 beginning from the early 1970s. In conclusion the article points out certain areas of electrosynthesis which deserve attention.

First electrosynthesis of transition metal peroxo complexes. Synthesis, characterization and reactivity of molybdenum and tungsten heteroligand peroxo complexes

Abstract Molecular peroxo complexes of molybdenum and tungsten, viz. [MO(O2)2L] (M = Mo or W; L = 2,2′-bipyridine, 1,10-phenanthroline or 2,2′-bipyridine-N,N′-dioxide), in the presence of hydrogen peroxide and then precipitating with the corresponding heteroligands. These complexes have also been prepared by the dissolution of metal powders in hydrogen peroxide. They have been characterized by elemental analysis and vibrational spectra. The complexes oxidize triphenylphosphine and triphenylarsine to triphenylphosphine oxide and triphenylarsine oxide, respectively.

Direct electrosynthesis of halo and mixed-halo complexes of palladium(II and IV) by the dissolution of a sacrificial palladium anode in aqueous medium

Abstract A rapid single-step method for the electrosynthesis of chloro and bromo complexes of palladium(II and IV), viz. M 2 [PdX 4 ] and M 2 [PdX 6 ], by the dissolution of a palladium anode in chloride or bromide containing media is described. Electrolysis of dilute HX solution in the presence of pyridine, 2,2′-bipyridyl or 1,10-phenanthroline gives rise to non-electrolytes, e.g. trans -[PdX 2 (py) 2 ], [PdX 2 (bipy)] and [PdX 2 (phen)]. Anodic oxidation of palladium in HX medium in the presence of acetonitrile and benzonitrile also gives the non-electrolytes trans -[PdX 2 (CH 3 CH 2 NH 2 ) 2 ] and trans -[PdX 2 (C 6 H 5 CH 2 NH 2 ) 2 ], respectively.

First electrosynthesis of transition metal peroxofluoro complexes. Synthesis, characterization and reactivity of some peroxofluoro complexes

Abstract Peroxofluoro complexes of the transition metals, viz. V, Nb, Ta, Mo and W, have been synthesized electrochemically using the sacrificial metal anodes in the presence of hydrogen peroxide (15%) and hydrofluoric acid (10%). These complexes have also been prepared by the dissolution of the metal powders in a mixture of hydrogen peroxide and hydrofluoric acid. While the monoperoxo complexes are formed at lower pH, higher pH is conducive to the formation of diperoxo complexes. The compounds have been characterized by elemental analysis and vibrational spectral studies. K2[MoO(O2)F4]·H2O and K2[WO(O2)F4]·H2O can oxidize triphenylphosphine to triphenylphosphine oxide in high yield.

Rhenium. Part XVI. Ammine and pyridine compounds of zinc and cadmium containing coordinated perrhenate

Summary[Zn(NH3)4](ReO4)2 and [Cd(NH3)4](ReO4)2 have been prepared from M(ReO4)2 and aqueous ammonia. The tetrapyridine compounds [Zn(py)4(ReO4)2] and [Cd(py)4(ReO4)2] have been obtained by reacting M(NO3)2 with aqueous pyridine followed by the addition of HReO4. Pyrolysis of these complexes gives [Zn(NH3)2(ReO4)2], [Cd(NH3)2(ReO4)2], [Zn(py)2(ReO4)2] and [Cd(py)2(ReO4)2] respectively. The kinetics of the decomposition steps: [ML4(ReO4)2] → [ML2(ReO4)2] → M(ReO4)2 have been studied from the t.g.a. curves. I.r. and Raman spectral and x-ray powder diffraction studies indicate that all the pyridine complexes and the two diammine complexes contain coordinated perrhenate, while the two tetrammine complexes contain ionic perrhenate.

Rhenium part XI. Mixed ligand complexes of tetra- and quinquevalent rhenium containing pyridine and bromide or iodide

Abstract Nonelectrolytic complexes [ReO(OH)py 2 X 2 ] (X = Br and I) have been isolated by the action of cold dilute HX on [ReO 2 py 4 ]Br·2H 2 O and [ReO 2 py 4 ] I·H 2 O. Hot and concentrated HBr produced [ReOpy 2 Br 3 ] and (pyH) 2 [ReBr 6 ] with [ReO 2 py 4 ]Br·2H 2 O whereas hot and concentrated HI gave [Repy 2 I 4 ] with [ReO 2 py 4 ]I·H 2 O. The thermal decomposition of [ReO 2 py 4 ]Br·2H 2 O and [ReO 2 py 4 ]I·H 2 O has been studied by thermogravimetry and the compound Re 2 O 7 py 2 has been isolated by isothermal heating of both the bromo and iodo salts. Molecular conductivities, magnetic susceptibility and i.r. spectra have been reported.

Electrosynthesis of transition metal fluoro complexes by the dissolution of a sacrificial metal anode

Abstract A general method for the electrosynthesis of anionic fluoro complexes of transition metals has been developed by the oxidation of sacrificial metal anodes in 20% HF medium at room temperature and at an applied potential of 2–8 V. Some mixed-valent complexes, e.g. Fe2F5·2H2O and Fe2F5·7H2O, have also been obtained by the same method. K2[MnF5]·H2O was obtained by subsequent electrolytic oxidation of the Mn(II) fluoro complex obtained in situ in the first step. The method is rapid and gives a good yield with high purity.

A rapid and direct electrochemical synthesis of K2[MoOF5]

Abstract A single-step synthesis of K2[MoOF5] has been made by the oxidation of a sacrificial molybdenum anode in a solution containing 20% HF followed by the addition of KF. This electrosynthesis represents a significant improvement over the existing methods.

Rhenium part XV. Tetragonal complexes of nickel(II) containing coordinated perrhenate [ReO4]−

SummaryThe compounds Ni(NH3)4(ReO4)2 and Ni(py)4(ReO4)2 prepared by reacting Ni(ReO4)2 with aqueous ammonia or pyridine, when heated at 150° give Ni(NH3)2(ReO4)2 and Ni(py)2(ReO4)2 respectively. The kinetics of the thermal decomposition of Ni(NH3)2(ReO4)2 has been studied. I.r., Raman and electronic spectra, x-ray powder diffraction and magnetic susceptibility measurements (at different temperatures) of the four compounds indicate that they are tetragonal complexes of NiII containing coordinated perrhenate.

Mass spectrometry of metal compounds. III. Electron-impact-induced mass spectrometric studies of bis(acetylacetonato)dioxomolybdenum(VI), MoO2(C5H7O2)2, and tetrakis(acetylacetonato)dioxo-μ-oxodimolybdenum(V), Mo2O3(C5H7O2)4

Abstract Electron-impact-induced mass spectra of MoO 2 (C 5 H 7 O 2 ) 2 , 1 , and Mo 2 O 3 (C 5 H 7 O 2 ) 4 , 2 , recorded at an ion-source temperature of 100°C show the molecular ion signals at m/z 328 and at m/z 636, respectively, indicating that they do not undergo association in the vapour state. The parent ion of 1 , unlike bis(acetylacetonato)metalates of the first-row transition metals, loses (CH 2 CO followed by C 3 H 5 O to produce [MoO 2 (C 5 H 7 O 2 )] + at m/z 229, the base peak, which ultimately fragments to [MoO 2 ] + . The molecular ion of 2 , [Mo 2 O 3 (C 5 H 7 O 2 ) 4 ] + , undergoes fragmentation following two different, but equally probable, pathways with one involving the loss of C 5 H 7 O 2 and C 5 H 7 O groups producing the ion [Mo 2 O 4 (C 5 H 7 O 2 ) 2 ] + , and the other involving the formation of the ion [MoO(acac) 2 ] + directly from the parent ion. The signal at m/z 312 owing to the ion [MoO(C 5 H 7 O 2 ) 2 ] + constitutes the base peak in the spectrum of 2 . Metastable transitions were studied, and the most probable fragmentation schemes for the compounds 1 and 2 are suggested. There is evidence for CH 3 shift from the ligand to the oxygen atoms bound to the metal centres or to form metal-carbon bonds.