文摘
Crystals of ASr2V3O3(Ge4O13)Cl, A = Na, K, were synthesized from high-temperature hydrothermal brines, and their structure and magnetic properties were investigated. These materials present a unique combination of a salt inclusion lattice, a polar crystal structure, and isolated V4+ (S = 1/2) trimer magnetic clusters. The structures consist of a trimeric V3O13 unit based on V4+ (S = 1/2), having rigorous 3-fold symmetry with a short V–V separation of 3.325(3) Å. The trinuclear V4+ units are formed by three edge shared VO6 octahedra sharing a central μ3-oxygen atom, which also imparts a polar sense on the structure. The V3O13 units are isolated from one another by tetranuclear Ge4O13 units, which are similarly arranged in a polar fashion, providing a unique opportunity to study the magnetic behavior of this triangular d1 system as a discrete unit. Magnetization measurements indicate spin-1/2 per V atom at high temperature, and spin-1/2 per V3 trimer at low temperature, where two V moments in each triangle are antiferromagnetically aligned and the third remains paramagnetic. The crossover between these two behaviors occurs between 20 and 100 K and is well-described by a model incorporating strong antiferromagnetic intra-trimer interactions and weak but nonzero inter-trimer interactions. More broadly, the study highlights the ability to obtain new materials with interesting structure–property relationships via chemistry involving unconventional solvents and reaction conditions.