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

Abstract 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 =  n Bu 4 N + , PPN + (bis(triphenylphosphoranylidene)ammonium); M = Ni(II) and Co(II)). The structures of n Bu 4 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 n Bu 4 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 n Bu 4 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(H 2 O) 2 [Au(CN) 2 ] 2 } ·  n Bu 4 N[Au(CN) 2 ] was obtained, a 2-D layered polymer that contains neutral sheets of {Co(H 2 O) 2 [Au(CN) 2 ] 2 } which are separated by n Bu 4 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  ∼ 2–3 cm −1 , zJ −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.