Formations of Mixed-Valence Oxovanadium^V,IV Citrates and Homocitrate with N-Heterocycle Chelated Ligand

Abstract

Dimeric mixed-valence oxovanadium citrate [V 2O 3(phen) 3(Hcit)].5H 2O ( 1) (H 4cit = citric acid, phen = 1,10-phenanthroline) was isolated from a weak acidic medium. It could be converted quantitatively into a tetrameric oxovanadium citrate adduct of 1,10-phenanthroline [V 2O 3(phen) 3(Hcit) 2(phen) 3O 3V 2].12H 2O ( 2). This was supported by the trace of infrared spectra and X-ray diffraction patterns. The two compounds feature a bidentate citrate group that chelates only to one vanadium center through their negatively charged alpha-alkoxy and alpha-carboxy oxygen atoms, while the other beta-carboxy and beta-carboxylic acid groups are free to participate in strong intramolecular and intermolecular hydrogen bonding [2.45(1) in 1 and 2.487(2) A in 2], respectively. This is also the case of homocitrato vanadate(V/IV) [V 2O 3(phen) 3( R, S-H 2homocit)]Cl.6H 2O ( 3) (H 4homocit = homocitric acid), which features a binding mode similar to that found in the R-homocitrato iron molybdenum cofactor of Mo-nitrogenase. Moreover, the homocitrato vanadate(V) [VO 2(phen) 2] 2[V 2O 4( R,S-H 2homocit) 2].4H 2O.2C 2H 5OH ( 4) is isolated as a molecular precursor for the formation of mixed-valence complex 3. The V-O alpha-alkoxy and V-O alpha-carboxy bond distances of homocitrate complexes 3 and 4 are 1.858(4) and 1.968(6) av and 2.085(4) and 1.937(5) A, respectively. They are shorter than those of homocitrate to FeVco (2.15 A). The gamma-carboxy groups of coordinated homocitrato complexes 3 and 4, and the free homocitrate salt Na 3(Hhomocit).H 2O ( 5), form strong hydrogen bonds with the chloride ion and the water molecule [2.982(5) in 3, 2.562(9) in 4, and 2.763(1) A in 5], respectively.

α-Hydroxy coordination of mononuclear vanadyl citrate, malate and S-citramalate with N-heterocycle ligand, implying a new protonation pathway of iron–vanadium cofactor in nitrogenase

“…The aforementioned assignments were also in consonance with previous reports of the other mononuclear citrate complexes like iron and manganese [39,40]. The features in the region of 950–990 cm −1 indicate the existence of V=O, which is in consistent with the values observed for the other vanadyl complexes [28–32]. …”

“…In the previous study of vanadium hydroxypolycarboxylate complexes, most of the investigations have addressed the coordination chemistry of citrate vanadates [17–25] and vanadyl complexes [25–31]. The mixed-ligand complexes have been reported as dimers [V 2 O 3 (phen) 3 (Hcit)]·5H 2 O, [V 2 O 3 (phen) 3 (Hcit) 2 (phen) 3 O 3 V 2 ]·12H 2 O [32] and monomer [VO(H 2 cit)(bpy)]·1.5H 2 O [33] (H 4 cit = citric acid, phen = 1,10–phenanthroline, and bpy = 2,2′–bipyridine). The formers are coordinated by citrate with α-alkoxy group, while the later is coordinated by citrate with α-hydroxy group.…”

Degradations of novel tetranuclear vanadyl glycollates to dinuclear species

“…The frequency difference ∆[ν as (COO -) -ν s (COO -)] [45] was greater than 200 cm -1 , which is consistent with the monodentate coordinated carboxy group, and in agreement with those observed from X-ray structural analysis. The aforementioned tentative assignments were in consonance with previous reports on α-hydroxycarboxylato complexes [14,15,17,21,28]. Moreover, the peaks around 932 ~ 988 cm -1 are assigned to V=O bond, which is in consistent with the values observed for the V-O containing dinuclear species [14,18,21,30].…”

“…Up to now, much work have been carried out to investigate the direct coordination chemistry of vanadium homocitrate [14,15], and its homologues citrate [15][16][17][18][19][20][21][22][23][24][25][26][27], malate [28,29], lactate [28] or glycollate [28,30,31]. These α-hydroxycarboxylates bind to the vanadium atom through their α-alkoxy, α-carboxy and/or β-carboxy groups.…”

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

“…The features in the region of 920–990 cm −1 indicate the existence of V=O bond, and are consistent with the values observed in other vanadium complexes. 38,41,43,80,81…”