Structural and Photoluminescent Properties of a Novel Terbium Bis(thiocyanato)aurate, Tb[Au(SCN)2]3·6H2O

The reaction of Tb3+ ions with KAu(SCN)2 results in the formation of the crystalline coordination compound Tb[Au(SCN)2]3·6H2O. Single-crystal X-ray diffraction has been employed to investigate the structural features of this compound. The crystallographic data are as follows (Mo Kα, λ = 0.71073 Å): orthorhombic, Cmcm, a = 12.4907(9) Å, b = 8.5845(6) Å, c = 20.7498(8) Å, V = 3679.72(16) Å3, Z = 4, R1(I > 2(σ)) = 0.0232. This material represents the first known example of a lanthanide dithiocyanatoaurate compound. Au(SCN)2− anions bridge Tb3+ centers in a bidentate fashion to form the [Tb(H2O)4(Au(SCN)2)2]͚+ 1D chains present in the structure. Trimeric Au units in the structure contain short aurophilic bonding interactions with distances of 3.1066(4) Å. The more common O–H‧‧‧O and O–H‧‧‧N H-bonding interactions in the structure are overshadowed by relatively rare O–H‧‧‧S interactions involving the bis(thiocyanato)gold(I) anions. Photoluminescence measurements illustrate that Tb[Au(SCN)2]3·6H2O displays strong Tb3+-based emission, but there is a lack of Au-based emission down to 85 K. Excitation spectra are recorded for the title compound and these measurements demonstrate the presence of a donor–acceptor process within the compound, leading to enhanced Tb3+-based emission.