Controlled Hydrothermal Synthesis and Structure-Property Relationships of Transition Metal Vanadates

This dissertation focuses on the synthesis and structure-property relationships of multi anionic transition metal vanadates. Hydrothermal synthesis methods have been optimized and used to obtain compounds with intriguing structural features. Ba2XCu(OH)[V2O7] with X = Cl, Br crystallizes in a new structure type (Pnma, a ≈ 15.1 Å, b ≈ 6.1 Å, c ≈ 9.6 Å) which features pseudo-honeycomb 2[Ba2X]3+ layers and isolated 1[CuO2/2(OH)2/2O2/1]5- chains. Two polymorphs of the M2(OH)[VO4] compound were obtained with M = Mn (Pnma, a = 14.911(1) Å, b = 6.1225(3) Å, c = 9.1635(5) Å) and M = Cu (P212121, a = 6.0564(1) Å, b = 8.5581(2) Å, c = 14.954(1) Å). These two structures are similar with respect to the M–O‒M connectivity, which results in corrugated layers. The M6+x(OH)3[VO4]4-2z[V2O7]z series of compounds with M = Mn, Co, Mg, and Fe crystallize in the acentric P63mc space group with lattice parameters a ≈ 12.9 - 13.2 Å, c ≈ 5.1 - 5.3 Å featuring a metal-based framework with isolated chains of face-sharing [MO6]-units. BaMn9[VO4]6(OH)2 crystallizes in the space group P213 with a = 12.8417(2) Å and has the unique structural feature of a chiral paddle-wheel. Further investigations of thermodynamic properties reveal for: i) Ba2XCu(OH)[V2O7] an antiferromagnetic quasi 1D S = 1/2 Heisenberg system; ii) Cu2(OH)[VO4] an antiferromagnetically coupled 2D lattice with ferrimagnetic long-range order; iii) M6+x(OH)3[VO4]4-2z[V2O7]z an antiferromagnetic framework ferrimagnetically coupled to the incorporated chains; iv) BaMn9[VO4]6(OH)2 a canted antiferromagnet due to geometrical frustration.