TRANSITION-METALS COMPLEXED TO ORDERED MESOPHASES .1. SYNTHESIS CHARACTERIZATION AND MESOMORPHIC PROPERTIES OF BINUCLEAR CYCLOPALLADATED PHENYLPYRIMIDINE SPECIES - CRYSTAL-STRUCTURE OF BIS((5-(1-HEXYL)-2-[(4'-METHOXY)PHENYL-2'-ATO]PYRIMIDINE-N',C2')-MU-ACETATO)DIPALLADUM(II)

To prepare new mesogenic materials, the dinuclear palladium(II) complexes [Pd(L)(mu-Cl)]2 have been synthesized by cyclometalation of the HLn species (HLn = 5-R-2-(4'-R'-phenyl)pyrimidine; HL1, R = C6H13, R' = CH3; HL2, R = C9H19, R' = CH3; HL3, R = C6H13, R' = C11H23; HL4: R = C9H19, R' = C9H19). With these complexes as precursors, a number of [Pd(L)(mu-X)]2 compounds (X = Cl, Br, I, OAc) have been obtained by metathetical reactions. The molecular structure of [Pd(L1)(mu-OAc)]2 has been determined by a single-crystal X-ray analysis. The crystals are triclinic, space group P1 with Z = 2. Unit cell parameters are a = 10.454 (1) angstrom, b = 13.229 (1) angstrom, c = 14.674 (2) angstrom, alpha = 80.20 (1)degrees, beta = 79.97 (1)degrees, gamma = 72.87 (1)degrees, V = 1894.5 (4) angstrom 3, D(calcd) = 1.36 g cm-3 for mol wt 869.62. Each palladium(II) ion in a square-planar geometry is bonded to a nitrogen atom and to an ortho carbon of pyridine and phenyl rings respectively (Pd(1)-N(2) = 2.013 (6) angstrom, Pd(2)-N(4) = 2.011 (5) angstrom; Pd(1)-C(1) = 1.947 (7) angstrom, Pd(2)-C(18) = 1.950 (7) angstrom) and to oxygen atoms of two different acetato groups (Pd(1)-O(1) = 2.142 (5) angstrom, Pd(1)-O(2) = 2.045 (5) angstrom; Pd(2)-O(3) = 2.159 (5) angstrom, Pd(2)-O(4) = 2.044 (5) angstrom). The two palladium coordination planes are folded at 25.66 (2)degrees with a Pd-Pd separation of 2.871 (1) angstrom. The HL2-HL4 ligands are nematic liquid crystals, while their mesogenic cyclopalladated derivatives display smectic mesophases only.