title: A spectroscopic study on the coordination and solution structures of the interaction systems between biperoxidovanadate complexes and the pyrazolylpyridine-like ligands.
abstract: In order to understand the substitution effects of pyrazolylpyridine (pzpy) on the coordination reaction equilibria, the interactions between a series of pzpy-like ligands and biperoxidovanadate ([OV(O2)2(D2O)](-)/[OV(O2)2(HOD)](-), abbrv. bpV) have been explored using a combination of multinuclear ((1)H, (13)C, and (51)V) magnetic resonance, heteronuclear single quantum coherence (HSQC), and variable temperature NMR in a 0.15 mol L(-1) NaCl D2O solution that mimics the physiological conditions. Both the direct NMR data and the equilibrium constants are reported for the first time. A series of new hepta-coordinated peroxidovanadate species [OV(O2)2L](-) (L = pzpy-like chelating ligands) are formed due to several competitive coordination interactions. According to the equilibrium constants for products between bpV and the pzpy-like ligands, the relative affinity of the ligands is found to be pzpy > 2-Ester-pzpy ≈ 2-Me-pzpy ≈ 2-Amide-pzpy > 2-Et-pzpy. In the interaction system between bpV and pzpy, a pair of isomers (Isomers A and B) are observed in aqueous solution, which are attributed to different types of coordination modes between the metal center and the ligands, while the crystal structure of NH4[OV(O2)2(pzpy)]·6H2O (CCDC 898554) has the same coordination structure as Isomer A (the main product for pzpy). For the N-substituted ligands, however, Isomer A or B type complexes can also be observed in solution but the molar ratios of the isomer are reversed (i.e., Isomer B type is the main product). These results demonstrate that when the N atom in the pyrazole ring has a substitution group, hydrogen bonding (from the H atom in the pyrazole ring), the steric effect (from alkyl) and the solvation effect (from the ester or amide group) can jointly affect the coordination reaction equilibrium.
authors.affiliation: Key Laboratory of Theoretical Chemistry and Molecular Simulation of Ministry of Education, Hunan Province College Key Laboratory of QSAR/QSPR, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China. yu_xianyong@163.com pgyi@hnust.cn.
authors.forename: Xian-Yong
authors.initials: XY
authors.lastname: Yu
authors.forename: Lin
authors.initials: L
authors.lastname: Deng
authors.forename: Baishu
authors.initials: B
authors.lastname: Zheng
authors.forename: Bi-Rong
authors.initials: BR
authors.lastname: Zeng
authors.forename: Pinggui
authors.initials: P
authors.lastname: Yi
authors.forename: Xin
authors.initials: X
authors.lastname: Xu
mesh_terms: D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011719:Pyrazines / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D014638:Vanadates / Q000737:chemistry*
chemical_list: D008024:Ligands; D011719:Pyrazines; D011725:Pyridines; D014638:Vanadates