Both complexes were characterized by elemental analysis, IR spectra, and single crystal X-ray crystallography. <...> The V atoms in the complexes have square pyramidal environment. <...> The substituent groups attached to the aromatic rings can influence the self-assembly of the complexes. <...> Vanadium complexes have received considerable attention in coordination chemistry [ 1—5]. <...> The interest to the study of the oxovanadium complexes stems from the discovery of two kinds of vanadium enzymes, vanadium-nitrogenases and vanadate-dependent haloperoxidases [ 6, 7 ]. <...> The insulin-like effect of vanadium complexes is another intriguing and promising feature that has further stimulated the vanadium coordination chemistry [ 8—10]. <...> In addition, a number of vanadium complexes have shown effective catalytic properties on sulfoxidation and epoxidation of olefins [ 11—16 ]. <...> Materials and methods. 3-Nitrobenzohydrazide and 2-hydroxy-1-naphthohydrazide were purchased from Alfa Aesar. [VO(acac)2] was prepared according to the literature method [ 17 ]. <...> Selected bond lengths and angles within the coordination sphere of vanadium are listed in Table 2. <...> A stirred solution of 3-nitrobenzohydrazide (0.181 g, 1 mmol) in absolute methanol (20 mL) was mixed with [VO(acac)2] (0.265 g, 1 mmol), and the resulting reaction mixture was refluxed on a water bath for 1 h, and then cooled to room temperature, yielding a deep brown solution. <...> The solution was kept still at ambient temperature for slow evaporation of the solvent, yielding brown crystals of 1. <...> A stirred solution of 2-hydroxy-1-naphthohydrazide (0.202 g, 1 mmol) in absolute methanol (20 mL) was mixed with [VO(acac)2] (0.265 g, 1 mmol), and the resulting reaction Table 1 Crystallographic data for the complexes Parameter 1 2 Formula C24H22N6O11V2 Formula weight Crystal system Space group a, b, c, Е 672.4 Monoclinic P2/n h, i, t, deg. <...> The solution was kept still at ambient temperature for slow evaporation of the solvent yielding brown crystals of 2. <...> On aerial oxidation in methanol, the VIV atom in VO(acac)2 is changed to VV in the complexes. 879 Table 2 Scheme 2. <...> The complex is an oxo-bridged dinuclear vanadium(V) complex, which possesses a crystallographic two-fold <...>