Andreas Loosli, Markus Wermuth and Hans-Ueli Güdel, Silvia Capelli, Jürg Hauser and Hans-Beat Bürgi
Crystal Structure and Optical Spectroscopy of Er₂[Pt(CN)₄]₃·21H₂O and Er₂[Pt(CN)₄]₂·SO₄·11.5H₂O
Inorg. Chem. 39, 2289-2293 (2000)                       

Abstract: We have synthesized two forms of erbium tetracyanoplatinates, Er₂[Pt(CN)₄]₃·21H₂O (red form) and Er₂[Pt(CN)₄]₂·SO₄·11.5H₂O (yellow form), and determined their crystal structures by X-ray diffraction. While the red form crystallizes in the orthorhombic space group Pbcn, with a = 15.4848(3) Å, b = 13.8186(2) Å, c = 19.07820(10) Å, a = b = g = 90°, and Z = 4, the yellow form precipitates in the tetragonal space group I4cm, with a = b = 14.321(2) Å, c = 13.338(3) Å, a = b = g = 90°, and Z = 4. Both forms show [Pt(CN)₄]^2- chains but differ markedly in color and morphology. This is due to the incorporation of sulfate ions in the latter modification, leading to an increased Pt-Pt distance. The observed optical absorption and emission behavior of the title compounds is correlated with the Pt-Pt distances.