As–Se Pentagonal Linkers to Induce Chirality and Polarity in Mixed-Valent Fe–Se Tetrahedral Chains Resulting in Hidden Magnetic Ordering

Abstract

A novel mixed-valent hybrid chiral and polar compound, Fe7As3Se12(en)6(H2O), has been synthesized by a single-step solvothermal method. The crystal structure consists of 1D [Fe5Se9] chains connected via [As3Se2]–Se pentagonal linkers and charge-balancing interstitial [Fe(en)3]2+ complexes (en = ethylenediamine). Neutron powder diffraction verified that interstitial water molecules participate in the crystal packing. Magnetic polarizability of the produced compound was confirmed by X-ray magnetic circular dichroism (XMCD) spectroscopy. X-ray absorption spectroscopy (XAS) and 57Fe Mössbauer spectroscopy showed the presence of mixed-valent Fe2+/Fe3+ in the Fe–Se chains. Magnetic susceptibility measurements reveal strong antiferromagnetic nearest neighbor interactions within the chains with no apparent magnetic ordering down to 2 K. Hidden short-range magnetic ordering below 70 K was found by 57Fe Mössbauer spectroscopy, showing that a fraction of the Fe3+/Fe2+ in the chains are magnetically ordered. Nevertheless, complete magnetic ordering is not achieved even at 6 K. Analysis of XAS spectra demonstrates that the fraction of Fe3+ in the chain increases with decreasing temperature. Computational analysis points out several competing ferrimagnetic ordered models within a single chain. This competition, together with variation in the Fe oxidation state and additional weak intrachain interactions, is hypothesized to prevent long-range magnetic ordering.This is a manuscript of an article published as Gamage, Eranga H., Saeed Kamali, Judith K. Clark, Yongbin Lee, Philip Yox, Padraic Shafer, Alexander A. Yaroslavtsev, Liqin Ke, Michael Shatruk, and Kirill Kovnir. "As–Se Pentagonal Linkers to Induce Chirality and Polarity in Mixed-Valent Fe–Se Tetrahedral Chains Resulting in Hidden Magnetic Ordering." Journal of the American Chemical Society 144, no. 25 (2022): 11283-11295. DOI: 10.1021/jacs.2c02936. Copyright 2022 American Chemical Society. Posted with permission. DOE Contract Number(s): AC02-07CH11358; DMR-2003783; DMR-1905499; AC02-05CH11231