Rational synthesis of unidimensional mixed valence solids. Structure oxidation state-charge transport relationships in iodinated nickel and palladium bisbenzoquinonedioximates

A detailed study is presented of crystal structure, stoichiometry, oxidation state, and electron transport in the materials Ni(bqd)2, Pd(bqd)2, Ni(bqd)2I0018, Ni(bqd)2I05 . S, and Pd(bqd)2I05 . S, where bqd = o-benzoquinonedioximato and S = an aromatic solvent. The compound Pd(bqd)2I050 . 0.52o-C6H4Cl2 was shown by single-crystal x-ray diffraction to crystallize in the tetragonal space group D/sub 4h/2-P4/mcc, with four formula units in a cell of dimensions a = 16.048 (7) and c = 6.367 (3) A. The crystal structure consists of stacked Pd(bqd)2 units, each staggered by 650 with respect to its nearest neighbors, and disordered chains of iodine atoms extending in the c direction. The Pd--Pd distance is 3.184 (3) A, Pd--N = 1.996 (7) A, and the Pd(bqd)2 units are rigorously planar. The predominant form of the iodine present is I3- (ν/sub fundamental/ 107 cm-1). Crystallization of Ni(bqd)2 from benzene containing traces of iodine produces the new orthorhombic phase Ni(bqd)2I0018. It crystallizes in the space group D/sub 2h/26-Ibam with four formula units in a unit cell of dimensions a = 16.438 (2), b = 14.759 (4), and c = 6.360 (2) A. Full-matrix least-squares refinement gave a final value of the conventional R index (on F) of 0.11 for 1026 reflections having F02 > 3 sigma(F02). The structure contains rigorously planar Ni(bqd)2 units stacked along the c axis with each molecule staggered by 680 with respect to its nearest neighbors. The Ni--Ni distance is 3.180 (2) A and Ni--N = 1.88 (10) A. Single-crystal electrical conductivity measurements (dc and 100-Hz ac) in the stacking direction show an increase in conductivity upon partial oxidation of >103 (Ni) and >104