The crystal and molecular structure of the binuclear complex, (μ-Acetato-O,O')[(μ-S)-α,α'-{(2-mercapto-4-methylbenzene-1,3-diyl)di(methylidyne)di(azino)}bis(cyclohexanemethanol)ato(3 -)]dipalladium(II), LPd₂(OAc), and its chloroform solvate, LPd₂(OAc)(CHCl₃)₂

Abstract

The crystal and nlolecular structures of the binuclear complexes LPd₂(OAc), and its chloroform solvate LPd₂(OAc)(CHC/₃)₂, have been determined by single-crystal X-ray diffraction techniques. These are the first reported structural analyses of binuclear complexes incorporating the quinquedentate ligand L^3-, which is derived from the condensation of cyclohexanecarbohydrazide with 2-(N,N-dimethylthiocarbamato)-5-methylisophthalaldehyde. The three-atom acetate bridging group is of special significance as all previous structure determinations of binuclear complexes containing ligands similar to L^3- have been restricted to those with either one or two-atom bridging groups. LPd₂(OAc) crystallizes in the triclinic space group P1 with a 15.513(1), b 22.238(2), c 8.0743(9) Ǻ, α 100.81(1), β 99.54(1) and γ 77.23(1)°, whilst the solvate is monoclinic, P2₁/c, a 14.668(2), b 9.448(1), c 25.483(2) Ǻ and β 95.39(1)°.

Both structures were solved by the normal Fourier methods and refined by least-squares methods which converged with R and R_w values of 0.044 and 0,051 for the 5084 independent, statistically significant reflections collected for LPd₂(OAc), and values of 0.063 and 0.066 for the 4883 reflections collected for the solvate. Both structures are quite similar with the acetate group bridging palladium centres which display similar distorted square-planar geometries, both within each molecule and between molecules of different structures. The internuclear Pd-Pd distance, av. 3.68 Ǻ, is the longest yet recorded for acetate-bridged, multinuclear palladium species and is attributed to the presence of the bulky thiophenoxide hinge.

The essential difference between the two structures lies in the contrast between the near planarity and approximate molecular mirror symmetry of the solvate compared with the less strained, asym- metrical V-shape of the non-solvate. This difference has been attributed to the different packing arrangement within the former, a consequence of the presence of the hydrogen-bonded solvent molecules.