Targeting [AuCl2(CN)2]− units as halophilic building blocks in coordination polymers
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.
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 [Au(CN)2]− and square planar [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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