Alkali-Metal Tuning of Chain Topology and Magnetic Order in V3+-Based Lead Vanadium Fluorides.

Two new V3+-based alkali metal lead fluorides, Na3.6Pb6.4V4F28 and K3.8Pb2.2V4F20, were synthesized via hydrothermal methods derived from the parent compound Pb7V4F26. Single-crystal X-ray diffraction reveals that Na3.6Pb6.4V4F28 crystallizes in the triclinic space group P1̅, featuring linear V-F-V chains within its structure, whereas K3.8Pb2.2V4F20 adopts the tetragonal space group P42/nmc and features a wavy zigzag chain structure. Magnetic and heat capacity measurements show that Na3.6Pb6.4V4F28 undergoes long-range antiferromagnetic ordering at 19.7 K, whereas K3.8Pb2.2V4F20 develops short-range antiferromagnetic correlations around 20 K. In contrast, the parent compound Pb7V4F26 shows no magnetic ordering below 2 K. These results demonstrate that alkali metal incorporation strongly reshapes the V-F-V chain geometry and local VF6-octahedral distortion, thereby tuning the uniformity of superexchange pathways and the dimensional growth of spin correlations in quasi-one-dimensional V3+-based fluorides.