Chains, Layers, and Twists: Structural Evolution in the VSn2-VSb2 Pseudo-Binary System

Single crystals of different V(Sn, Sb)2 phases were grown via the self-flux method by employing an excess of Sn and Sb. The obtained crystals were studied using X-ray diffraction and EDX spectroscopy, which revealed the existence of two new ternary phases and two solid solutions based on the binary VSn2 to VSb2 phases, showing peculiar multi-step structural evolution upon going from the VSn2 side to the VSb2 side of the system. The first novel phase τ1 crystallizes in the monoclinic unit cell, while the second phase—τ2—adopts an orthorhombic crystal structure. The discovered phases derive their structure from the parent phases VSn2 and VSb2 and are built from linear chains of fused V(Sn, Sb)8 antiprisms. These chains are then coupled into layers, which are stacked either right on top of each other or with a 60° twist. The twists are supported by Sn atoms located at a boundary between the layers. Thus, upon going from VSn2 to VSb2, the number of twists per layer decreases from one in VSn2 to 2/3 in τ1, and to 1/2 in τ2, ultimately ending at zero in VSb2. While the Sn atoms have a larger radius compared to that of Sb, the volume per one atom decreases in the VSnx′Sb2−x′ solid solution with increasing Sn content before returning to the expected increase in the τ1-τ2-VSn2−xSbx sequence. The decrease in volume in the former is caused by the decrease in V-V distances inside the chains, which is caused by the change in character of the V-E interactions, where Sb atoms form two-center V-Sb bonds, while Sn atoms act as bridges forming three-center V-Sn-V bonds, as revealed by our DFT calculations.