Ferromagnetic Exchange Coupling of Vanadium(IV) dπ Spins across Pyrimidine Rings:  Dinuclear Complexes of Oxovanadium(IV) Bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionate) Bridged by Pyrimidine Derivatives

• Published in: Inorganic chemistry 2001-12, Vol.40 (27), p.7059-7064
• Main Authors: Ishida, Takayuki, Mitsubori, Shin-ichi, Nogami, Takashi, Takeda, Naoya, Ishikawa, Masayasu, Iwamura, Hiizu
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic010730n

Dinuclear oxovanadium(IV) complexes bridged by pyrimidine derivatives, L[VO(hfac)2]2 [L = pyrimidine (PM), 4-methylpyrimidine (MPM), 4,6-dimethylpyrimidine, 4-aminopyrimidine, and quinazoline; hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dionate], were synthesized and characterized. All of them showed intramolecular ferromagnetic interaction, and the magnetic susceptibilities were analyzed on the basis of the singlet−triplet model, giving 2J/k B = 2.2−5.5 K. PM[VO(hfac)2]2 crystallized in a monoclinic space group C2/c with a = 34.092(2), b = 6.9783(4), and c = 16.4940(9) Å, β = 109.104(1)°, V = 3707.8(4) Å3, and Z = 4 for C24H8F24N2O10V2, and MPM[VO(hfac)2]2 gave isomorphous crystals. A semiempirical calculation study based on the determined structure suggests the presence of dπ−pπ interaction between vanadium and pyrimidine nitrogen atoms. Ferromagnetic coupling is explained in terms of a spin-polarization mechanism across the pyrimidine bridge. The intermolecular ferromagnetic interaction of PM[VO(hfac)2]2 can be interpreted by the contact between the spin-polarized pyrimidine moiety and the oxovanadium oxygen atom in an adjacent molecule.