NMR Study On The Interactions Between Diperoxovanadates And Pyridine-like Ligands

Vanadium complexes, particularly vanadates and recently reportedperoxovanadate compounds, have encouraged many interests because the vanadiumcould be as an inorganic co-factor or catalytic center discovering many enzymes withkey roles in haloperoxidation, nitrogen fixation, and elsewhere. In this paper, wemake full use of multinuclear (1H,13C and51V), magnetic resonance (COSY, HSQCand HMBC), variable temperature NMR, as well as theoretical calculations toinvestigated interactions between [OV(O2)2(D2O)]/[OV(O2)2(HOD)](bpV) andpyridine-like ligands. The coordination rules and the structures of new-formed specieswere explored. The experiment results coulded be summarized as follows:1. In order to understand the substitution effects of pyridine-like ligands oncoordination equilibrium, the coordination interactions between a series ofbisubstituted pyridine-like ligands and peroxovanadium(V)[OV(O2)2(D2O)]/[OV(O2)2(HOD)] in solution have been investigated by multinuclear (1H,13C and51V)magnetic resonance and HSQC. A series of new six-coordinate peroxovanadatecomplxes [OV(O2)2LL’]n (LL′=bisubstituted pyridine-like ligands, n=1) have beenobserved, and the coordination ability of bisubstituted pyridines toperoxovanadium(V) is3,4-dimethylpyridine>4,5-dimethylpyridine>pyridine-3,5-dicarboxylate>>2,3-dimethylpyridine. The coordination interactionsamong title system have been further studied by DFT(density functionaltheory)calculations, and there results indicate that solvent may play an important rolein these coordination interactions.2. To understand the coordination modes and the solution structure of5-amino-1,10-phenanthroline (5-NH2-phen) on the coordination reaction equilibrium,the coordination reaction between peroxovanadium (V) complex [OV(O2)2(D2O)]/[OV(O2)2(HOD)] and5-NH2-phen has been investigated by the multinuclear (1H,13Cand51V) magnetic resonance, variable temperature NMR, HSQC and HMBC. Theexperimental results indicated that a pair of isomers has been observed in solution,which suggested that there are two different typles of cooridinarion betweenvanadium atom and5-NH2-phen. The solution structure of these new-formedperoxovanadate species were proposed based on direct NMR experimentalinformation and confirmed by the theoretical caculations. Moreover, the result ofdensity functional caculations indicate that solvent effects may play an important partin these interactions.3. In order to explore the substitution effects of pyrazoly pyridine (pzpy) on the coordination reaction equilibria, the interactions between a series of the pzpy-likeligands and the biperoxidovanadate ([OV(O2)2(D2O)]/[OV(O2)2(HOD)], bpV) havebeen explored by a combination of multinuclear (1H,13C and51V) magnetic resonance,heteronuclear single quantum coherence (HSQC), as well as variable temperatureNMR in a0.15mol/L NaCl deuteroxide solution that mimics the physiologicalcondition. A series of new hepta-coordinated peroxidovanadate species [OV(O2)2L](L=pzpy-like chelating ligands) are formed due to the competitive coordinationinteractions. According to the equilibrium constants for products between bpV and thepzpy-like ligands, the relative affinity of the ligands is pzpy>2-Ester-pzpy2-Me-pzpy2-Amide-pzpy>2-Et-pzpy. In the interaction system between bpV andpzpy, a pair of isomers (Isomer A and B) are observed, which indicated that there aretwo different types of coordination modes between the metal center and the ligands.These results demonstrate that, when the N atom in pyrazole ring has a substitutiongroup, the hydrogen bonding (form H atom in pyrazole ring), the steric effect (fromalkyl) and the solution effect (from ester or amide group) can affect the coordinationreaction equilibrium.