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 = nBu4N+, PPN+ (bis(triphenylphosphoranylidene)ammonium); M = Ni(II) and Co(II)). The structures of nBu4N{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 nBu4N{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 nBu4N+ 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} · nBu4N[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 nBu4N[Au(CN)2] layers; aurophilic interactions of 3.4250(13) Å 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 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.

Graphical abstractStudies on the templating effect of the cation and the resulting impact on the magnetic properties were conducted on a series of [cation]{M[Au(CN)2]3} coordination polymers. Despite the high-dimensionality structures, no significant magnetic coupling was observed, suggesting that the [Au(CN)2] bridging unit behaves as a poor mediator of magnetic exchange in these systems.Figure optionsDownload full-size imageDownload as PowerPoint slide