Orthomolybdates in the Cs–FeII,III–Mo–O System: Cs4Fe(MoO4)3, Cs2Fe2(MoO4)3 and CsFe5(MoO4)7

Abstract

AbstractThree new complex molybdenum oxides – Cs2Fe2(MoO4)3, Cs4Fe(MoO4)3 and CsFe5(MoO4)7 – with average oxidation states of Fe +2 and +2.6 were obtained during a study of phase formation in the system Cs–FeII,III–Mo–O and investigated by X‐ray single‐crystal analysis at room temperature and 100 K. The structure of cubic Cs2Fe2(MoO4)3 [P213, a = 10.9161(2) Å, Z = 4] is very similar to the one of pseudocubic Cs2Co2(MoO4)3 with a weak orthorhombic distortion. Hexagonal Cs4Fe(MoO4)3 [P$\bar {6}$2c, a = 6.2922(16) Å, c = 23.937(13) Å, Z = 2] is isostructural to the high‐temperature modification of Rb4Mn(MoO4)3. CsFe5(MoO4)7 crystallizes in monoclinic symmetry [P21/m, a = 6.9239(6) Å, b = 21.4477(19) Å, c = 8.6374(8) Å, β = 101.667(2)°, Z = 2] and represents a new structure type. This structure contains three crystallographically independent Fe sites and consists of isolated FeO6 octahedra and Fe4O18 units of edge‐sharing FeO6 octahedra, which are connected with MoO4 tetrahedra through corners, thus forming a three‐dimensional framework. CsFe5(MoO4)7 orders magnetically with a ferromagnetic component at TC = 10 K, proposed as a canted antiferromagnet. Its antiferromagnetic structure at 0 T was described by combination of two propagation vectors k = (1/2, 0, 0) and k = (0, 0, 0) with magnetic moments of 2.6, 1.6 and 3.5 μB for three independent Fe sites. Two magnetic‐field‐induced transitions are observed at 0.25 and 1.9 T at 2 K.