A LAXS (Large Angle X-ray Scattering) and EXAFS (Extended X-ray Absorption Fine Structure) Investigation of Conductive Amorphous Nickel Tetrathiolato Polymers

Abstract

The structure of amorphous partially oxidized nickel tetrathiolato polymers has been studied by EXAFS and LAXS (large angle X-ray scattering). These polymers are the following: (i) the poly(nickel ethylenetetrathiolates) with different countercations, referred to as [(Ni-ett)Na0.31]n(1a), [(Ni-ett)K0.25]n (lb), [(Ni-ett)(n-Bu4N)0.75]n (1c), and [(Ni-ett)(Co(pmi)2)0.5]n(1d); (ii) the poly(nickel tetrathiafulvalenetetrathiolates), [(Ni-ttftt)Na0.3]n(2a) and [(Ni-ttftt)(Bu4N)0.5]n(2b); and the poly(nickel tetrathiosquarate), [(Ni-tts)K0.15]n(3). An EXAFS study of 1a shows that the nickel atom is surrounded by four sulfur atoms (Ni-S = 2.169 (8) Å) and four carbon atoms (Ni-C = 3.06 (1) Å). This result is the first experimental evidence, in such polymers, that ett acts as a bischelating ligand on two metal atoms. LAXS investigations of all polymers confirm this structure in the first coordination sphere and give additional information on the polymer chain packing. The studied polymers exhibit two types of structural arrangement. The packing in type I polymers (1a, 1b, 1d, 2a, and 3) is the most dense and consists of coplanar parallel polymer chains located in parallel planes. The chains are stacked perpendicularly to their plane and eclipsed. The interchain distances within a plane (interstack) vary between 3.7 and 4.3 Å and the interplanar stacking distances (intrastack) between 3.8 and 5.7 Å. In type II polymers (1c and 2b) the chains are also stacked perpendicularly to their plane (stacking distance = 4.3-4.4 Å) but the interstack distances are much larger (>10 Å). The type of structural arrangement of a polymer is not solely determined by the nature of the tetrathiolato bridging ligand but by those of the countercation. This result can be rationalized in terms of isolobal analogy of the metal d8 (Ni2+), the ethylene (C24+), and the squarate (C46+) fragments. The experimental density of the polymers and their electrical conductivity are correlated with their structural arrangement. © 1988, American Chemical Society. All rights reserved.