Magnetochemistry: advances in theory and experimentation

Zero-field splitting in metal complexes

Syntheses of new porous frameworks with specific pore size and type are of considerable interest for the appearance of zeolite-like functionalities. It is useful to take advantage of metal complex-assembled compounds because of designable frameworks, high microporosity, and flexible frameworks based on a variety of coordination geometries of metal centers and multifunctionality of bridging organic parts. Many recent reports show that the synthesis procedures are developing from serendipitious to rational level. Therefore, the micropore chemistry of metal complex-based assemblages is directed toward not only new frameworks but also functionalities such as gas and small molecule adsorption, ion exchange, heterogeneous catalysis, photo-chemical and -physical properties. For chemical and physical functionalities robustness of a framework is required even in the absence of guest molecules in the cavity. The stability is largely dependent on the structural dimensionality of the assemblages. A wide variety of st...

Functional Micropore Chemistry of Crystalline Metal Complex-Assembled Compounds

The article deals with coordination compounds of iron(II) that may exhibit thermally induced spin transition, known as spin crossover, depending on the nature of the coordinating ligand sphere. Spin transition in such compounds also occurs under pressure and irradiation with light. The spin states involved have different magnetic and optical properties suitable for their detection and characterization. Spin crossover compounds, though known for more than eight decades, have become most attractive in recent years and are extensively studied by chemists and physicists. The switching properties make such materials potential candidates for practical applications in thermal and pressure sensors as well as optical devices. The article begins with a brief description of the principle of molecular spin state switching using simple concepts of ligand field theory. Conditions to be fulfilled in order to observe spin crossover will be explained and general remarks regarding the chemical nature that is important for the occurrence of spin crossover will be made. A subsequent section describes the molecular consequences of spin crossover and the variety of physical techniques usually applied for their characterization. The effects of light irradiation (LIESST) and application of pressure are subjects of two separate sections. The major part of this account concentrates on selected spin crossover compounds of iron(II), with particular emphasis on the chemical and physical influences on the spin crossover behavior. The vast variety of compounds exhibiting this fascinating switching phenomenon encompasses mono-, oligoand polynuclear iron(II) complexes and cages, polymeric 1D, 2D and 3D systems, nanomaterials, and polyfunctional materials that combine spin crossover with another physical or chemical property.

/pdf/spin-state-switching-in-iron-coordination-compounds-42yuqvvfsi.pdf

Spin state switching in iron coordination compounds

Constructing magnetic molecular solids by employing three-atom ligands as bridges

Spin-crossover ferric complexes: unusual effects of grinding and doping solids

The preparation and characterization of a series of spin-crossover ferric complexes with the composition [Fe(X-SalEen)2]Y, where X-SalEen results from the Schiff-base condensation of X-substituted salicylaldehyde and N-ethylethylenediamine, are reported. Several of the complexes exhibit a gradual, but complete, spin-crossover transition from high spin to low spin in the solid state, whereas certain complexes exhibit an incomplete transition and there is a “plateau” in the Ffl/Fe vs. temperature curve. One compound, [Fe(3-OCH~-SalEen)2]PF6, experiences a sudden spin-crossover phase transition. The conversion from high spin to low spin occurs within a 2’ range around the temperature 159 K. A sensitivity of physical properties to exact compound preparation is demonstrated. In spite of the variation in the series, it is shown by variable-temperature s7Fe MBssbauer and EPR techniques that only two electronic states, the high-spin 6A, excited state and one low-spin Kramers doublet ground state, are thermally populated for any of the compounds. There is no evidence of an intermediate-spin state. The ground-state Kramers doublet in these complexes has one unpaired electron in an orbital which is largely d,.. in composition.

Spin-Crossover Ferric Complexes: Curiosities Observed for Unperturbed Solids

Magnetic exchange interactions in binuclear transition-metal complexes bridged by imidazolate, benzimidazolate, biimidazolate, and bibenzimidazolate ions

Muin S. Haddad

Papers

Spin-crossover ferric complexes: unusual effects of grinding and doping solids

Spin-Crossover Ferric Complexes: Curiosities Observed for Unperturbed Solids

Magnetic exchange interactions in binuclear transition-metal complexes bridged by imidazolate, benzimidazolate, biimidazolate, and bibenzimidazolate ions

Crystal structure and magnetic properties of bis(pyrazine)copper(II) perchlorate, Cu(pyz)2(ClO4)2, a two-dimensional Heisenberg antiferromagnet

An explanation of unusual properties of spin-crossover ferric complexes