Structure and Emissive Properties of Heterobimetallic Ln–Au Coordination Polymers: Role of Tb and Eu in Non-aurophilic [nBu4N]2[Ln(NO3)4Au(CN)2] versus Aurophilic Ln[Au(CN)2]3·3H2O/3D2O Chains

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.