Studies on polyhalides .25. Triiodides of pyridine complexes of divalent palladium: Di(pyridine)palladium hexaiodide Pd(py)(2)I-6 and two forms of tetra(pyridine)palladium hexaiodide Pd(py)(4)I-6

Two forms of the new compound Pd(py)(4)I-6 have been prepared by the reaction of stoichiometric amounts of PdCl2, C5H5N, KI and I-2 in water. One modification crystallizes triclinically in space group <P(1)overbar> with a = 907.7(3), b = 960.5(7), c = 992.0(4) pm, alpha = 117.31(4), beta = 103.35(3), gamma = 86.01(5)degrees and Z = 1, the other orthorhombically in space group Pnnm with a = 891.6(4), b = 1047.6(4), c = 1659.1(5) pm and Z = 2. Both structures may be described as layerlike packings of I-3(-) anions and [Pd(py)(4)](2+) cations. Differences arise from the orientations of the anions and cations within these layers. The new compond Pd(py)(2)I-6 has been prepared by recrystallisation of Pd(py)(4)I-6 from chloroform. It crystallizes in the monoclinic space group I2/a with a = 1801.1(4), b = 584.0(1), c = 2220.5(6) pm, beta = 115.78(2)degrees and Z = 2. The structure is built up from quasi square planar complexes [Pd(py)(2)I-2] and iodine molecules I-2 linked together to give alternating screw- and zigzag-shaped chains 1 infinity[I-. I-2] along [1 0 0] forming nets of type (10, 3) including the Pd2+ ions. The structure may also be described as a layerlike packing of the anionic chains 1 infinity[I-. I-2]and linear complex cations [Pd(py)(2)](2+) parallel [0 1 1].