Interplay between the structural and magnetic probes in the elucidation of the structure of a novel 2D layered [V4O4(OH)2(O2CC6H4CO2)4]·DMF

Abstract

The title compound has been synthesized under solvothermal conditions by reacting vanadium(V) oxytriisopropoxide with terephthalic acid in N,N-dimethylformamide. A combination of synchrotron powder diffraction, infrared spectroscopy, scanning and transmission electron microscopy, and thermal and chemical analysis elucidated the chemical, structural and microstructural features of a new 2D layered inorganic–organic framework. Due to the low-crystallinity of the final material, its crystal structure has been solved from synchrotron X-ray powder diffraction data using a direct space global optimization technique and subsequent constraint Rietveld refinement. [V₄O₄(OH)₂(O₂CC₆H₄CO₂)₄]·DMF crystallizes in the monoclinic system (space groupP2/m (No. 10)); cell parameters: a = 20.923(4) Å, b = 5.963(4) Å, c = 20.425(1) Å, β = 123.70(6)°, V = 2120.1(9) ų, Z = 2. The overall structure can be described as an array of parallel 2D layers running along [−101] direction, consisting of two types of vanadium oxidation states and coordination polyhedra: face-shared trigonal prisms (V⁴⁺) and distorted corner-shared square pyramids (V⁵⁺). Both configurations form independent parallel chains oriented along the 2-fold symmetry crystallographic b-axis mutually interlinked with terephthalate ligands in a monodentate mode perpendicular to it. The morphology of the compound exhibits long nanofibers, with the growth direction along the layered [−101] axis. The magnetic susceptibility measurements show that the magnetic properties of [V₄O₄(OH)₂(O₂CC₆H₄CO₂)₄]·DMF can be described by a linear antiferromagnetic chain model, with the isotropic exchange interaction of J = −75 K between the nearest V⁴⁺ neighbours of S = 1/2.