DINUCLEAR COMPOUNDS OF TITANIUM(III) AND ZIRCONIUM(III), WITH AND WITHOUT METAL-METAL BONDS

Four new dinuclear compounds, three of titanium and one of zirconium, have been prepared and characterized structurally and magnetically. Al l four have edge-sharing bioctahedral structures with two Cl atoms in the bridging positions. Two of the titanium compounds are of the type Ti2[RNC(H)NR]2[mu-RNC(H)NR]2(mu-Cl)2, with R = phenyl, 1, and biphenyl , 2. Both of these show distinct structural indications of Ti-Ti bondi ng and the magnetic susceptibility of 2 shows that there are np unpair ed electrons. Compound 1 crystallizes from a toluene:THF (1:1) solutio n in the triclinic space group P1BAR with unit cell dimensions a = 11. 788(2) angstrom b = 12.464(3) angstrom c = 9.548(1) angstrom alpha = 1 11.94(1)-degree, beta = 92.98(1)-degree, gamma = 114.64(1)-degree, V = 1146.5(4) angstrom3 for Z = 1. The structure was refined to R = 0.045 4 and Rw = 0.0674 for 2684 reflections with I > 3sigma(I). Compound 2 crystallizes from a toluene/THF (1:1) solution in the monoclinic space group P2 1/c with unit cell dimensions a = 16.564(4) angstrom b = 16. 472(6) angstrom c = 18.541(6) angstrom beta = 109.03(2)-degree, V = 47 83(3) A3 for Z = 2. The structure was refined to R = 0.0696 and R(w) = 0.0883 for 2471 reflections with I > 3 sigma(I). The stoicheiometric analogues, M2Cl6(PMe3)4, where M = Ti and Zr have also been prepared a nd examined. The Zr compound, 3, shows clear evidence for the presence of a Zr-Zr single bond while the Ti compound, 4, has both structural [Ti ... Ti = 3.740 (3) angstrom] and magnetic properties (mu(eff) at 2 95 K per Ti atom of 1.52beta) signaling that no Ti-Ti bond exists. Com pound 3 crystallizes from a benzene solution in the monoclinic space g roup P2(1)/n with unit cell dimensions a = 10.518(2) angstrom b = 12.9 94(2) angstrom c = 11.131(2) angstrom beta = 94.09(1)-degree, V = 1517 .4(4) angstrom3 for Z = 2. The structure was refined to R = 0.0475 and R(w) = 0.0642 for 1435 reflections with I > 3sigma(I). Compound 4 cry stallizes from a benzene solution in the orthorhombic space group Pnma with unit cell dimensions a = 11.571(2) angstrom b = 13.703(2) angstr om c = 18.585(3) angstrom V = 2946.9(6) angstrom3 for Z = 4. The struc ture was refined to R = 0.0494 and R(w) = 0.0735 for 1158 reflections with I > 3sigma(I).