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 [(Bu4N)-Bu-n](2)[Ln(x)Gd(1-x)(NO3)(4)Au(CN)(2)] (Ln = Eu, Tb; x = 0.01, 0.02, 0.04, 0.08) and [(Bu4N)-Bu-n](2)[EuxTb1-x(NO3)(4)Au(CN)(2)] (x = 0.25, 0.5, 0.75), as well as the analogous solid-solutions of aurophilic Ln(x)Gd(1-x)[Au(CN)(2)](3)center dot 3H(2)O and EuxTb1-x[Au(CN)(2)](3)center dot 3H(2)O. The single-crystal structures of M[Au(CN)(2)](3)center dot 3H(2)O (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 [(Bu4N)-Bu-n] 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)center dot 3D(2)O frameworks, it was shown that the O-H vibrational energy in the hydrated (aurophilic) samples can partially quench the Ln signal.