Synthesis, structure and magnetic properties of 2-D and 3-D [cation] {M[Au(CN)2]3} (M = Ni, Co) coordination polymers

In order to study the templating effect of the cation and the resulting impact on the magnetic properties, reactions of M(II) salts with [cation][Au(CN)(2)] were conducted, yielding a series of coordination polymers of the form [cation]{M[Au(CN)(2)](3)} (cation = (Bu4N+)-Bu-n, PPN+ (bis(triphenylphosphoranylidene)ammonium); M = Ni(II) and Co(II)). The structures of (Bu4N)-Bu-n{M[Au(CN)(2)](3)} and PPN{M[Au(CN)(2)](3)} (M = Ni and Co) contain two distinct 3-D anionic frameworks of {M[Au(CN)(2)](3)}(-), hence the framework was sensitive to the cation, but not to the identity of the metal center. In (Bu4N)-Bu-n{M[Au(CN)(2)](3)}, the metal centers are connected by [Au(CN)(2)] units to form six 2-D (4, 4) rectangular grids that are fused through the M centers to yield a complex three-dimensional framework which accommodates the (Bu4N+)-Bu-n cations. In PPN{M[Au(CN)(2)](3)}, the framework adopts a simpler non-interpenetrated Prussian-blue-type pseudo-cubic array, with the PPN+ cations occupying each cavity; no reduction in dimensionality occurs despite the large cation size. In the presence of water, {Co(H2O)(2)[Au(CN)(2)](2)} center dot (Bu4N)-Bu-n[Au(CN)(2)] was obtained, a 2-D layered polymer that contains neutral sheets of {Co(H2O)(2)[Au(CN)(2)](2)} which are separated by (Bu4N)-Bu-n[Au(CN)(2)] layers; aurophilic interactions of 3.4250(13) A and hydrogen-bonding connect the layers. The magnetic properties of all compounds were investigated by SQUID magnetometry. The Ni(II) polymers have similar magnetic behaviour, which are dominated by zero-field splitting with very weak antiferromagnetic interactions at low temperature (D similar to 2-3 cm(- 1), zJ < 1 cm(-1)). The magnetic behaviour of all of the Co(II) polymers were found to be very similar, and dominated by single-ion effects (i.e. a large first-order orbital contribution). No significant magnetic coupling is observed in any of these coordination polymers, suggesting that the [Au(CN)(2)] bridging unit behaves as a poor mediator of magnetic exchange in these high-dimensionality systems. (c) 2006 Elsevier Ltd. All rights reserved.