The preparation and structural characterization of two trinuclear vanadium complexes, (V-3(mu(3)-O)O-2)(mu(2)-O2P(CH2C6H5)(2))(6)(H2O), 1, and (V-3(mu O3-)O-2)(mu(2)-O2P(CH2C6H5)(2))(6)(py), 2, are reported. In these nonclassical structures, the planar central core consists of the three vanadium atoms arranged in the form of an acute quasi-isosceles triangle with the central oxygen atom multiply bonded to the vanadium atom at the center of the vertex angle and weakly interacting with the two other vanadium atoms on the base sites, each of which contain one external multiply bonded oxygen atom. Reacting VO(acac)(2) in the presence of diphenylphosphinic acid affords (VO(O2Ph2)(2))(infinity), 3, while 2-hydroxyisophosphindoline-2-oxide at room temperature in CH2Cl2 affords ((H2O)VO(O2Po-(CH2)(2)C6H4)(2))(infinity), 4, and at 120 degrees C in EtON yields (VO(O2P(o(CH2)(2)(C6H4))(infinity), 5 on the basis of elemental analyses. The thermal and chemical stability of the complexes were assessed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements. The bond strengths of the vanadium atoms to the OH2 ligand in 1 and to the NC5H5 ligand in 2 were assessed at 10.7 and 42.0 kJ/mol respectively. Room temperature magnetic susceptibility measurements reveal magnetic moments for trinuclear 1 and 2 at 3.02(1) and 3.05(1) mu(B/mol), and also close to spin only values (1.73 mu(B)) values for 3, 4, and 5 at 1.77(2), 1.758(7), and 1.77(3) mu(B), respectively. Variable-temperature, solid-state magnetic susceptibility measurements were conducted on complex 2 in the temperature range of 2.0-298 K and at an applied field of 0.5 T. Magnetization measurements at 2 and 4 K confirmed a very weak magnetic interaction between the vanadyl centers.