Structure and magnetism of fluorides Cs2MCu3F10 (M = Mg, Mn, Co, Ni), variants of the CsCu2F5 type

X-ray structure determinations of single crystals showed that compounds Cs2MCu3F10 crystallize with Z = 2 in space group P2(1)/n (No. 14) (M = Mn) of the CsCu2F5 type resp, in its super-group 12/m (No.12) (M = Mg, Co, Ni). Cs2MgCu3F10: a = 714.9(1), b = 736.8(1), c = 940.4(1)pm, b = 96.29(1)degrees, (Mg-F: 199.2 pm), Cs2MnCu3F10: a = 725.1(1), b = 742,7(1), c = 951.0(2) pm, b = 97.28(3)degrees, (Mn-F: 209.1 pm); Cs2CoCu3F10: a = 717.8(3), b = 739.1(2), c = 939.4(4) pm, b = 97.49(2)degrees, (Co-F: 203.1 pm); Cs2NiCu3F10: a = 716.3(1), b = 737.7(1), c = 938.2(2) pm, b = 97.09(1)degrees, (Ni-F: 201.0 pm). As determined directly for the Mg compound and generally concluded from the average distances M-F noted, M substitution concerns mainly the octahedrally coordinated position of the CsCu2F5 structure, the distortion of which is very much reduced thereby. Within the remaining [CuF4] and [CuF5] coordinations, in contrast to CsCu2F5, one F ligand is disordered, in case of the Mn compound the pyramidally coordinated Cu atom, too. The magnetic properties are complex and point to frustration and spin glass effects. Only at the diamagnetically substituted variants with M = Mg, Zn no Neel point appears, which is reached at 27, 23, 36 and 55 K for M = Mn, Co, Ni and Cu, resp.. At lower temperatures ferri- resp. weak ferromagnetism and hysteresis is observed.