STUDIES ON POLYHALIDES .25. TRIIODIDES OF PYRIDINE COMPLEXES OF DIVALENT PALLADIUM - DI(PYRIDINE)PALLADIUM HEXAIODIDE PD(PY)(2)I-6 AND 2 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 r eaction of stoichiometric amounts of PdCl2, C5H5N, KI and I-2 in water . One modification crystallizes triclinically in space group <P(1)over bar> 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 ort horhombically 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 layerlik e packings of I-3(-) anions and [Pd(py)(4)](2+) cations. Differences a rise from the orientations of the anions and cations within these laye rs. The new compond Pd(py)(2)I-6 has been prepared by recrystallisatio n of Pd(py)(4)I-6 from chloroform. It crystallizes in the monoclinic s pace group I2/a with a = 1801.1(4), b = 584.0(1), c = 2220.5(6) pm, be ta = 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 infini ty[I-. I-2] along [1 0 0] forming nets of type (10, 3) including the P d2+ ions. The structure may also be described as a layerlike packing o f the anionic chains 1 infinity[I-. I-2]and linear complex cations [Pd (py)(2)](2+) parallel [0 1 1].