The Relationship Between Octahedral and Trigonal-Prismatic Coordination in Bis Tridentate Complexes of TiIV and VIV

The crystal structures of two vanadium complexes V( aabh )2 (1) and V( aasalh )2 (2) and of two titanium complexes Ti( aabh )2 (3) and Ti( babh )2 (4), where aabh is the dinegative, tridentate ligand pentane-2,4-dione benzoylhydrazonato (2-), aasalh is pentane-2,4-dione salicyloylhydrazonato (2-) and babh is 4-phenylbutane-2,4-dione benzoylhydrazonato (2-), were determined by X-ray diffraction methods. Crystals of (1) are monoclinic, space group P21/c, a 8.906(3), b 11.840(2), c 22.450(6)Ǻ, β 97.72(3)°, V 2345.8 and Z 4; those of (2) are triclinic, space group Pī , a 9.802(4), b 10.205(3), c 13.688(6)Ǻ, α 100.56(3),β 94.07(4),γ 112.89(3)°, V 1224.6 Ǻ3 and Z 2; those of (3) are monoclinic, space group C2/c, a 18.543(4), b 10.269(4), c 12.589(4)Ǻ, β 106.80(2)°, V 2294.9 Ǻ3 and Z 4; and those of (4) are monoclinic, space group P21/n, a 10.923(4), b 19.139(3), c 14.610(5)Ǻ, β 94.54(3)°, V 3044.7 Ǻ3 and Z 4. The structures were refined by a full-matrix least-squares procedure in each case to final values of R 0.102, 0.044, 0.049 and 0.058 for the structures (1), (2), (3) and (4), respectively, and values of Rw 0.099, 0.049, 0.053 and 0.065 for 1735, 3405, 1185 and 2911 statistically significant reflections, respectively. In the vanadium complexes the coordination geometry is approximately trigonal prismatic, whereas in each of the titanium complexes the two tridentate ligands are in a meridional arrangement with an approximately octahedral coordination. The stabilization of vanadium(IV) in the absence of the oxo function and the role of the metals in producing different coordination geometries are discussed.