Thermal expansion in 3d-metal Prussian Blue Analogs-A survey study

We present a comprehensive study of the structural properties and the thermal expansion behavior of 17 different Prussian Blue Analogs (PBAs) with compositions M(3)(II)[(M')(III)(CN)(6)](2) center dot nH(2)O and M(2)(II)[Fe(II)(CN)(6)] center dot nH(2)O, where M(II) = Mn, Fe, Co, Ni, Cu and Zn, (M')(III) = Co, Fe and n is the number of water molecules, which range from 5 to 18 for these compounds. The PBAs were synthesized via standard chemical precipitation methods, and temperature-dependent X-ray diffraction studies were performed in the temperature range between -150 degrees C (123 K) and room-temperature. The vast majority of the studied PBAs were found to crystallize in cubic structures of space groups Fm (3) over barm, F (4) over bar 3m and Pm (3) over barm. The temperature dependence of the lattice parameters was taken to compute an average coefficient of linear thermal expansion in the studied temperature range. Of the 17 compounds, 9 display negative values for the average coefficient of linear thermal expansion, which can be as large as 39.7 x (1)0(-6) K(-1) for Co(3)[Co(CN)(6)](2)center dot 12H(2)O. All of the M(3)(II)[Co(III)(CN)(6)](2)center dot nH(2)O compounds show negative thermal expansion behavior, which correlates with the Irving-Williams series for metal complex stability. The thermal expansion behavior for the PBAs of the M(3)(II)[Fe(III)(CN)(6)](2) center dot nH(2)O family are found to switch between positive (for M = Mn, Co, Ni) and negative (M = Cu, Zn) behavior, depending on the choice of the metal cation (M). On the other hand, all of the M(2)(II)[Fe(II)(CN)(6)] center dot nH(2)O compounds show positive thermal expansion behavior. (C) 2011 Elsevier Inc. All rights reserved.