N-heterocycle chelated oxomolybdenum(VI and V) complexes with bidentate citrate

Abstract

A 1,10-phenanthroline (phen) chelated molybdenum(VI) citrate, [(MoO2)2O(H2cit)(phen)(H2O)2] x H2O (1) (H4cit = citric acid), is isolated from the reaction of citric acid, ammonium molybdate and phen in acidic media (pH 0.5-1.0). A citrato oxomolybdenum(V) complex, [(MoO)2O(H2cit)2(bpy)2] x 4H2O (2), is synthesized by the reduction of citrato molybdate with hydrazine hydrochloride in the presence of 2,2'-bipyridine (bpy), and a monomeric molybdenum(VI) citrate [MoO2(H2cit)(bpy)] x H2O (6) is also isolated and characterized structurally. The citrate ligand in the three neutral compounds uses the alpha-alkoxy and alpha-carboxy groups to chelate as a bidentate leaving the two beta-carboxylic acid groups free, that is different from the tridentate chelated mode in the citrato molybdate(VI and V) complexes. 1 and in solution show obvious dissociation based on 13C NMR studies.

Preliminary Assignment of Protonated and Deprotonated Homocitrates in Extracted FeMo-Cofactors by Comparisons with Molybdenum(IV) Lactates and Oxidovanadium Glycolates

“…The complexes' C−O(H) stretching frequencies in Table 2 can serve as references for the C−O(H) vibrations in FeMoco. The oxidation state of Mo atom in FeMo-co was assigned as Mo(IV) 74 and Mo(III) 75,76 58 1.419 (8) 1086m The peak at 1672 cm −1 in extracted FeMo-co IR is assigned to the asymmetric vibration ν as (CO 2 61 It was assigned only to NMF in the previous reference. 9 We therefore assign this peak to ν as (CO 2 − ) of extracted FeMo-co and the NMF absorptions.…”

“…Most of the previous glycolate, lactate, malate, citrate, or homocitrate bind to vanadium or molybdenum via α-alkoxy and α-carboxy and/or β-carboxy groups, − while only a small number of complexes were isolated coordinating via α-hydroxy (protonated) and α-carboxy groups. ,− As the homocitrates in the cofactors have a bidentate coordination, protonated and deprotonated molybdenum/vanadium α-hydroxycarboxylates with the similar local structures are critical for comparisons with the FeMo/V-cos and for a better clarification of their coordination environments. In this publication, we report the successfully isolated protonated and deprotonated pair of mononuclear glycolato oxidovanadium complexes: [VO­(Hglyc)­(phen)­(H 2 O)]­Cl·2H 2 O ( 1 ) and [VO­(glyc)­(bpy)­(H 2 O)] ( 2 ) (H 2 glyc = glycolic acid, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline).…”

Isolated Mixed-Valence Iron Vanadium Malate and Its Metal Hydrates (M = Fe2+, Cu2+, Zn2+) with Reversible and Irreversible Adsorptions for Oxygen

“…Their structural, electronic, and electrochemical properties were investigated in depth. In addition, the homocitrate in nitrogenase is another research focus − which has been widely modeled by metal homocitrato homologues. − In this report, we have used malic acid, a homologue of homocitrate, as an auxiliary ligand to obtain the isolated octanuclear Fe 2 V 6 cluster (NH 4 ) 3 (NH 3 CH 3 ) 3 [Fe III 2 V IV/V 6 O 11 (mal) 6 ]·7.5H 2 O ( 1 ). Its skeleton shows some similarity to the configuration of the FeV-cofactor in vanadium nitrogenase.…”

Assignment of protonated R-homocitrate in extracted FeMo-cofactor of nitrogenase via vibrational circular dichroism spectroscopy

“…Most reported homocitrate and its homologues bind to molybdenum via α-alkoxy, α-carboxy, and/or β-carboxy groups 11,[31][32][33][34][35][36][37][38][39][40][41] . Several molybdenum α-hydroxycarboxylates were isolated coordinating via α-hydroxy (protonated) and α-carboxy groups 31,42,43 .…”