Reduction of structural dimensionality through incorporation of auxiliary ligands in lanthanide tetracyanoplatinates

The synthesis of a series of lanthanide tetracyanoplatinates containing the auxiliary ligands 1,10′-phenanthroline (phen) or 2,2′-bipyridine (bpy) have been carried out by reaction of Ln3+ nitrate salts with phen or bpy and potassium tetracyanoplatinate in solvent systems containing dimethylsulfoxide and dimethylformamide. The use of these solvents has lead to the isolation of [{Ln(DMSO)2(C12H8N2)(H2O)3}2Pt(CN)4](Pt(CN)4)2·2C12H8N2·4H2O (Ln = Eu (Eu-1), Tb (Tb-1), Yb(Yb-1)), [Ln(DMF)3(C12H8N2)(H2O)2NO3]Pt(CN)4 (Ln = La (La-2), Eu (Eu-2), Tb (Tb-2)), and [Ln(DMF)3(C10H8N2)(H2O)2NO3]Pt(CN)4 (Ln = La (La-3), Sm (Sm-3), Eu (Eu-3), Tb (Tb-3)) in the form of single crystals. Single-crystal X-ray diffraction has been used to investigate their structural features. The use of DMSO versus DMF as the solvent results in markedly different structural features. Eu-1 contains [{Eu(DMSO)2(C12H8N2)(H2O)3}2Pt(CN)4]2+ complex cations where the two Eu3+ centers are linked by a trans-bridging Pt(CN)42− anion to form a dimeric lanthanide complex cation. An additional uncoordinated Pt(CN)42− anion balances charge. Eu-2 and Eu-3 consist of zero-dimensional salts with [Eu(DMF)3(C12H8N2)(H2O)2(NO3)]2+ or [Eu(DMF)3(C10H8N2)(H2O)2(NO3)]2+ complex cations, respectively, and only non-coordinated Pt(CN)42− anions. Photoluminescence measurements illustrate that the Eu3+ and Tb3+ compounds for all three structure types display enhanced emission due to intramolecular energy transfer from the coordinated cyclic amines.