Crystal structures and Raman spectra of Cu(OH)F and Cu3(OH)2F4

Abstract Crystals of Cu(OH)F and Cu 3 (OH) 2 F 4 have been synthesized at low-hydrothermal conditions in sizes up to 0.3 mm. The structures were solved from CCD X-ray single-crystal data and refined to R = 0.033 and 0.019, respectively. Cu(OH)F: space group P 2 1 / a , Z = 4, a = 5.301(1) Å, b = 6.376(1) Å, c = 5.074(1) Å, β = 112.90(1)°, and V = 157.98(5) Å 3 . Cu 3 (OH) 2 F 4 : space group P 2 1 / n , Z = 2, a = 5.501(1) Å, b = 4.766(1) Å, c = 8.462(1) Å, β = 92.28(1)°, and V = 221.68(7) Å 3 . In both compounds the copper atoms are 4 + 2 coordinated to their ligands ( Jahn-Teller distortion). Cu(OH)F is isotypic to Cu(OH)Cl, forming layers of edge-sharing Cu(OH) 3 F 3 polyhedra, which are interconnected by hydrogen bonds. The structure of Cu 3 (OH) 2 F 4 is characterized by chains of edge-sharing Cu(OH) 2 F 4 polyhedra running along [1 0 0], which are linked to each other via corners to form a framework. Hydrogen bonds of the type O—H···F occur with O···F distances of 2.619 and 2.697 Å in Cu(OH)F and Cu 3 (OH) 2 F 4 , respectively. The observed O—H stretching frequencies of 3129 and 3306 cm –1 , respectively, in Raman spectra are in excellent agreement with expected values from distance — frequency correlations. Moreover, the pleochroism of the bands corresponds in both compounds to the O—H orientation found in the structure determination.