Effect of Stereochemically Active Electron Lone Pairs on Magnetic Ordering in Trivanadates

Stereochemically active electron lone pairs derived fromp-block cations represent a versatile geometric and electronic structuremotif that can be used to tune Fermi surfaces of periodic solids.In this study, we contrast s- and p-block monovalent trivanadatesand demonstrate that lone-pair repulsions and concomitant latticeanharmonicity drive anisotropic structural distortions, which in turnmodulates magnetic ordering of electrons on the trivanadate host framework. Stereoactive electron lone pairs derived from filled5/6s(2) states of p-block cations are an intriguing electronicand geometricstructure motif that have been exploited for diverse applicationssuch as thermoelectrics, thermochromics, photocatalysis, and nonlinearoptics. Layered trivanadates are dynamic intercalation hosts, wherethe insertion of cations can be used to tune electron correlation,charge localization, and magnetic ordering. However, the interactionof 5/6s(2) stereoactive electron lone pairs with layeredtrivanadates remains unexplored. In this study, we contrast s- andp-block trivanadates and map off-centering in the coordination environmentand reduction in symmetry arising from the stereochemical activityof lone pair cations to the emergence of filled antibonding lone-pair6s(2)-O 2p hybridized states. The former is studiedby high-resolution single-crystal X-ray diffraction studies of TlV3O8 and isostructural RbV3O8 to probe distinct differences in Tl and Rb coordination environmentsand the resulting modulation of V-V interactions in V3O8 slabs. The latter has been probed by variable-energyhard X-ray photoelectron spectroscopy (HAXPES) measurements, whichmanifest orbital-specific contributions from bonding and antibondinginteractions of stereoactive Tl 6s(2) electron lone pairsin TlV3O8. The spectroscopic assignment of valenceband states to stereoactive lone pairs is further corroborated byfirst-principles electronic structure calculations, crystal orbitalHamilton population analyses, and electron localization function maps.The presence of the Tl 6s(2) electron lone pair in TlV3O8 brings about the off-centering of Tl+ cations, which leads to anisotropy in Tl-O bonds. The off-centeringof Tl ions weakens V-O bonds in one direction, which subsequentlystrengthens directional V-V coupling. Magnetic measurementsreveal ferromagnetic signatures for both RbV3O8 and TlV3O8. However, the differences in V & BULL;& BULL;& BULL;Vinteractions significantly affect the energy balance of the superexchangeinteractions, resulting in an ordering temperature of 140 K for TlV3O8 as compared to 125 K for RbV3O8. The results demonstrate the distinctive effects of stereochemicallyactive lone pairs in modifying electronic structure near the Fermilevel and for mediating superexchange interactions.

Automated summary

This study compares s- and p-block monovalent trivanadates and demonstrates that lone-pair repulsions and lattice anharmonicity drive anisotropic structural distortions, which in turn modulate magnetic ordering of electrons on the trivanadate host framework. The stereoactive electron lone pairs derived from filled 5/6s(2) states of p-block cations have diverse applications and play a crucial role in modifying electronic structure and mediating superexchange interactions.