Study of the coordination and solution structures for the interaction systems between diperoxidovanadate complexes and 4-(pyridin-2-yl)pyrimidine-like ligands

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 41; no. 13; pp. 3684 - 3694
• Main Authors: Yu, Xian-Yong, Yi, Ping-Gui, Ji, Dan-Hong, Zeng, Bi-Rong, Li, Xiao-Fang, Xu, Xin
• Format: Journal Article
• Language: English
• Published: England 07.04.2012
• Subjects: Coherence; Crystal structure; Hydrogen Bonding; Isomers; Ligands; Nuclear magnetic resonance; Organometallic Compounds - chemistry; Peroxides - chemistry; Pyridines - chemistry; Pyrimidines - chemistry; Rings (mathematics); Solutions; Steric effects; Vanadates - chemistry
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c2dt12334g

To understand the substitution effects of 4-(pyridin-2-yl)pyrimidine (pprd) on the coordination reaction equilibria, the interactions between a series of the pprd-like ligands and [OV(O(2))(2)(H(2)O)](-) or [OV(O(2))(2)(HOD)](-) or [OV(O(2))(2)(D(2)O)](-) (bpV) have been explored by 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 D(2)O solution that mimics physiological conditions. The direct NMR data are reported for the first time. Competitive coordination interactions result in a series of new hepta-coordinated peroxidovanadate species [OV(O(2))(2)LL'](-) (LL' = pprd-like chelating ligands). The equilibrium constants for the products between bpV and the pprd-like ligands show that the relative affinity of the ligands is pprd ≈ 2-NH(2)-pprd > 2-Me-pprd > 2-Et-pprd > 4-(6-methylpyridin-2-yl)pyrimidine (abbr. 6'-Me-pprd). When the ligand is pprd, a pair of isomers (Isomer A and B) are observed in aqueous solution, which are attributed to the different types of coordination modes between the metal and the ligands, while the crystal structure of NH(4)[OV(O(2))(2)(pprd)]·2H(2)O has the same coordination structure as Isomer A. For substituted pprd ligands, however, only one type of structure (Isomer A or B ) is observed in solution. These results demonstrate that, when the aromatic ring has a substitution group, both the steric effect (from the alkyl) and hydrogen bonding (from the amine) can affect the coordination reaction equilibrium to prevent the appearance of either Isomer B in solution for the ligands 2-Me-pprd, 2-NH(2)-pprd, 2-Et-pprd, or Isomer A in solution for 6'-Me-pprd.