Novel tetracyanoplatinates with the larger Ln3+ ions: Synthesis, structures, and photoluminescence properties of KLn[Pt(CN)4]2·8.75H2O (Ln = La, Pr, Nd)

The reaction of the larger Ln3+ ions with K2Pt(CN)4·3H2O results in the formation of the crystalline coordination compounds KLn[Pt(CN)4]2·8.75H2O (Ln = La, Pr, Nd). The structures of these compounds have been determined by single-crystal X-ray diffraction and found to be isostructural. Crystallographic data (Mo Kα, λ = 0.71073 Å) for the representative La compound (LaPt): orthorhombic, Fdd2, a = 19.5826(3) Å, b = 26.8725(7) Å, c = 34.9729(8) Å, V = 18 403.9(7) Å3, Z = 32, R1(I > 2σ(I)) = 0.0217. The structures of the compounds contain nearly planar two-dimensional lanthanide tetracyanoplatinate layers formed from the trans-bridging of the Ln3+ cations by tetracyanoplatinate (TCP) anions. The layers are graphitic in nature, containing fused hexagons that form the layered 2-D topology. Furthermore, they stack in an ABCDEFGHA pattern, are separated by an average distance of 3.3591(7) Å, and contain multiple interlayer Pt⋯Pt interactions that give rise to one-dimensional stacks of TCP. All three compounds display strong broad-band luminescence in the visible region originating from the TCP stacks. At room temperature, LaPt illustrates strong green emission centered at 508 nm upon excitation in the UV. The broad emission splits into a stronger band at 534 nm and a higher energy band at 478 nm upon cooling the crystals to 77 K. The extent of splitting was found to depend on the excitation wavelength. Similar spectral features at both room temperature and 77 K are observed in the PrPt system. A characteristic feature of NdPt is that the TCP-based broad emission is significantly quenched due to reabsorption of the emitted light by the Nd3+ ion, indicating the dominance of a radiative process within the system.