Intermolecular exchange interaction in bis-(phenoxy Schiff base) Co(ii) complexes: an in-depth insight into the magneto-structural nature of single-molecule magnets

Abstract

Single-ion magnets (SIMs) are the most promising candidates for magnetic storage and processing of information at the molecular level. Apart from the properties of each isolated SIM, their performance crucially depends on intermolecular exchange interactions in bulk materials or those occurring when individual SIMs are assembled into arrays for practical applications. However, compared with their magnetic anisotropy, the correlation of in-bulk intermolecular exchange interactions and magnetic relaxation parameters has been established to a much lesser extent. In this work, using an extended protocol involving XRD, multifrequency and frequency-domain EPR, SQUID magnetometry, DFT and ab initio calculations, we investigated intermolecular interactions in a new series of four bis-(phenoxy Schiff base) Co(II) complexes representing field-induced SIMs. Combined multifrequency EPR ranging from 9 GHz to >1 THz allowed unique measurement of weak intermolecular exchange couplings of the order of 0.01 cm⁻¹. Consolidation of EPR data with ac/dc SQUID magnetometry and detailed structural and quantum-chemical analyses allowed us to reliably analyze the key performance characteristics of these SIMs, the degree of polyhedral distortion, and the values of intermolecular exchange couplings in an attempt to achieve a firm interplay among them. Such analysis can become prototypical for future design and evaluation of crystals, assemblies and arrays of SIMs.