In the quest for nano-sized materials with potential applications in new technologies and devices, the molecular magnetism based on coordination systems shows a valuable path, including the idea of structure-property rationales. Polynuclear coordination compounds are already in the range of nanometers and many consecrated magnetic materials that can be prepared at nano-scale granulation, such as oxides, have as bonding and exchange coupling mechanisms the same causal engines identified in coordination systems. Based on this paradigm, several case studies are taken, relating the magnetic properties with methods of electron structure calculations and phenomenological models.
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The coordination chemistry, (Lawrance, 2010) based on medium strength bonds providing -by versatility- a large structural variety, is a domain that can naturally respond to the challenge of building systems at nanoscale, (Klabunde, 2001; Nabok, 2005) following line-forces of the supramolecular paradigm. (Lehn, 1995; Ariga & Kunitake, 2006) Besides, since the rationales relating the structural features with specific manifestations are relatively well understood, by dedicated phenomenological schemes, either as qualitative thumbrules, or even as explicit models, one may say that half of the way to the desiderata of predicting useful properties is already paved with useful pieces of knowledge, in the part starting from the molecular level, up to the medium sized systems. Particularly, a very subtle balance of the factors belonging to the chemical environment and electron configuration of the metal ions occurs in the case of lanthanide-based systems. In this domain we hold pioneering advents in approaching the electron structure of lanthanide complexes and lattices, establishing rational structure –property relationships useful as leverages in the newly contoured domain of spintronics (Ferbinteanu & Cimpoesu, 2014).
To build a system behaving as magnet at molecular or nano-scale, some prerequisites must be fulfilled, a key role belonging to the magnetic anisotropy, (Sessoli & Powell, 2009; Cucinotta et al., 2012; Ruamps et al., 2013) which is related in complex manner with certain asymmetry features of the environment around the metal ions. The first Single Molecule Magnets (SMMs) (Christou, Gatteschi, Hendrickson, & Sessoli, 2000; Gateschi and Sessoli, 2003) were large polynuclear complexes, genuinely nano-scale objects, although in meanwhile smaller edifices were identified with this behaviour. The Single Chain Magnets (SCMs) (Gatteschi & Vindigni, 2014) are 1D relatives of SMMs, whose nature is actually based on the intrinsic SMM features of the repeating unit, the phenomenon implying a correlation length of few molecular sequences, as well as the subtle role of inter-molecular non-covalent effects. The SMMs and SCMs are mesoscale congeners of the bulk magnetic materials which can be taken as relevant case studies in establishing rational structure –property relationships useful as leverages in the newly contoured domain of spintronics.
Aside the magnetic anisotropy, the magnetic behavior is also modulated by exchange effects that are deciding the final properties at extended scale. The molecular magnetism was born several decades ago (Kahn, 1993; Coronado, Delhaès, Gatteschi, & Miller, 1996; Miller & Drillon, 2001) translating at molecular scale problems basically known from solid state physics and adding a supplement of understanding at the level of underlying microscopic mechanisms. Nowadays is the time to remake the reverse route, reinvesting the insight gained at molecular stage back into the extended systems of the currently expanding nano-sciences realm.
Placing on equal footing the experimental and theoretical chemistry, one may draw a red line in the concern of understanding and predicting magnetic properties. Using examples from our own chemical synthetic outcome, or relevant prototypic cases from literature, we propose a walk on the borderline of chemistry and physics of extended coordination systems.