Structure and Emissive Properties of Heterobimetallic Ln–Au Coordination Polymers: Role of Tb and Eu in Non-aurophilic [<sup>n</sup>Bu<sub>4</sub>N]<sub>2</sub>[Ln(NO<sub>3</sub>)<sub>4</sub>Au(CN)<sub>2</sub>] versus Aurophilic Ln[Au(CN)<sub>2</sub>]<sub>3</sub>·3H<sub>2</sub>O/3D<sub>2</sub>O Chains
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This investigation is focused on comparing photophysical properties between two series of lanthanide-dicyanoaurate coordination polymers that contain and lack aurophilic interactions, respectively. Luminescence and crystallographic studies have been carried out on five different coordination polymer chain frameworks: the non-aurophilic [nBu4N]2[LnxGd1–x(NO3)4Au(CN)2] (Ln = Eu, Tb; x = 0.01, 0.02, 0.04, 0.08) and[nBu4N]2[EuxTb1–x(NO3)4Au(CN)2] (x = 0.25, 0.5, 0.75), as well as the analogous solid-solutions of aurophilic LnxGd1–x[Au(CN)2]3·3H2O and EuxTb1–x[Au(CN)2]3·3H2O. The single-crystal structures of M[Au(CN)2]3 ·3H2O (M = Eu, Gd) are also reported for comparison. In the aurophilic frameworks the close proximity of gold(I) centers on neighboring chains allows for Au–Au interactions to take place that facilitate energy transfer between lanthanides. Terbium- and europium-doped aurophilic frameworks show energy transfer between one of the lanthanide ions and dicyanoaurate centers as observed via luminescence measurements. In the non-aurophilic frameworks the [nBu4N] cations separate the Au–Au chains, thereby preventing interaction between them, and preventing energy transfer. By preparing the aurophilic EuxTb1–x[Au(CN)2]3·3D2O frameworks, it was shown that the O–H vibrational energy in the hydrated (aurophilic) samples can partially quench the Ln signal.
