Elsevier

Inorganica Chimica Acta

Volume 403, 1 July 2013, Pages 127-135
Inorganica Chimica Acta

Targeting [AuCl2(CN)2] units as halophilic building blocks in coordination polymers

https://doi.org/10.1016/j.ica.2013.02.011Get rights and content

Abstract

Several new [AuCl2(CN)2]-containing complexes were synthesized with a range of ancillary ligands and first row transition metals. Use of Cu(II) and 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (Me2phen) with [nBu4N][AuCl2(CN)2] yielded the ionic compounds [Cu(phen)2(OHMe)][AuCl2(CN)2]2 (1) and {Cu(Me2phen)2[AuCl2(CN)2]}[AuCl2(CN)2] (2). Use of 2,2;6,2-terpyridine (terpy) and Cu(NO3)2·3H2O or Cu(ClO4)2·6H2O instead yielded Cu(terpy)[AuCl2(CN)2]2 (3) and Cu(terpy)(μ-ClO4)[AuCl2(CN)2] (4), respectively. Compound (3) is molecular, with a single terpy ligand and two pendant [AuCl2(CN)2] units bound to a Cu(II) centre, whereas 4 is a linear 1-D coordination polymer consisting of Cu(II) centres bridged by ClO4- moieties. Using Cu(II) and pyrazine (pyz) generates a 1-D coordination polymer, Cu(pyz)(NCMe)2[AuCl2(CN)2]2·2MeCN (5) with bridging pyz units and pendant [AuCl2(CN)2] and NCMe moieties. Upon switching to 4,4′-bipyridine (bipy), the 3-D coordination polymer, {Cu(bipy)2[Au(CN)2]}[AuCl2(CN)2] (6) results, which is built up of sheets of Cu(II)/bipy units bridged by [Au(CN)2]. Free [AuCl2(CN)2] anions sit in the network cavities, held by a rare, unsupported AuIAuIII interaction of 3.4530(10) Å. The inability of [AuCl2(CN)2] to act as a bridging unit in any of these ancillary ligand-containing structures is consistent with the behaviour of [AuBr2(CN)2] in previous studies and shows that [AuCl2(CN)2] holds no advantages over [AuBr2(CN)2] in coordination polymer formation. In the absence of ancillary ligands, molecular Mn(OH2)4[AuCl2(CN)2]2 (7) and the 1-D coordination polymer Co(OH2)4[AuCl2(CN)2]2·2H2O (8), the first coordination polymer with [AuCl2(CN)2] as the primary bridging moiety, were also prepared and structurally characterized.

Graphical abstract

Eight new [AuCl2(CN)2]-based materials were synthesized and structurally characterized. Four show ionic or molecular structures, whereas the other four are coordination polymers. Co(OH2)4[AuCl2(CN)2]2·2H2O represents the first coordination polymer containing [AuCl2(CN)2] as a bridging moiety. In one case, a rare AuI⋯AuIII interaction of 3.4530(10) Å was observed.

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Highlights

► Eight new [AuCl2(CN)2]-based materials were synthesized and structurally characterized. ► Structures included four new ionic and molecular species and four new coordination polymers. ► Co(OH2)4[AuCl2(CN)2]2·2H2O is the first coordination polymer with the [AuCl2(CN)2] building block. ► A rare AuI⋯AuIII interaction of 3.4530(10) Å was observed in one case.

Introduction

Coordination polymers have become an increasingly important class of materials due to the ability to rationally design them through the strategic choice of metals, building blocks (bridging moieties) and ancillary ligands [1], [2], [3], [4], [5], [6], [7]. Gold-containing cyanometallate species, specifically linear d10 [Au(CN)2] and square planar d8 [Au(CN)4] have been used in a range of coordination polymer structures with potentially useful properties such as magnetism [8], [9], [10], [11], [12], [13], birefringence [14], [15], [16] and vapochromism [17], [18], [19], [20], [21]. The halophilic [AuBr2(CN)2] was recently shown to enhance birefringent properties [14] as a result of the polarizable Au–Br bonds, and its propensity to form intermolecular Br⋯Br interactions that help to align structural units. However, these studies also found that [AuBr2(CN)2] was weakly Lewis basic, and as a result, it did not readily bridge metals to form coordination polymers, especially when paired with competing chelating ancillary ligands.

In this context we investigated the related [AuCl2(CN)2] unit in terms of its ability to form coordination polymers and the impact of potential Cl⋯Cl interactions [22], [23] on the resulting structures as a comparison with the Br-analogue. The results, which include the first molecules and coordination polymers incorporating [AuCl2(CN)2] are reported herein.

Section snippets

Structure of [nBu4N][AuCl2(CN)2]

The crystal structure of K[AuCl2(CN)2] has been previously described as having separated K+ cations and [AuCl2(CN)2] ions, with N(cyano) moieties interacting with the K+ cations [24]. Substitution of the K+ cations in K[AuCl2(CN)2] for nBu4N+ cations resulted in [nBu4N][AuCl2(CN)2] [25]; the structure also shows separated cations and anions with no Cl⋯Cl or Au⋯Cl interactions present (Fig. 1). The [AuCl2(CN)2] anion features standard Au–Cl and Au–C bonds of 2.284(2)–2.289(2) Å and

Conclusions

In this study, the ability of [AuCl2(CN)2] to form coordination polymers when combined with some first row transition metals and with or without a variety of heterocyclic amine ancillary ligands was investigated, and compared to the analogous [AuBr2(CN)2]. In the presence of ancillary ligands, most complexes formed contained metal centres nearly saturated by the ancillary ligand, leaving little or no room for the [AuCl2(CN)2] units to bind. In the cases where [AuCl2(CN)2] was able to bind,

General procedures

Caution! Perchlorate salts are potentially explosive and are powerful oxidants. Although no difficulties have been experienced, they should be handled with care. Chlorine should only be used in a well-ventilated fumehood.

All reactions were performed in air. K[AuCl2(CN)2] [44], [28], Mn(OH2)2[Au(CN)2]2 [12] and Co(OH2)2[Au(CN)2]2 [12] were synthesized as previously reported. All other reagents were obtained from commercial sources and used as received.

Infrared spectra were measured on a Thermo

Acknowledgements

The authors thank NSERC of Canada for financial support. J.S.O. is grateful to NSERC for a PGS-D doctoral scholarship and to Natural Resources Canada for an internship.

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