Whereas there are hundreds of known iron(II) spin-crossover compounds, only a handful of cobalt(II) spin-crossover compounds have been discovered to date, and hardly an in depth study on any of them exists. This review begins with an introduction into the theoretical aspects to be considered when discussing spin-crossover compounds in general and cobalt(II) systems in particular. It is followed by case studies on [Co(bpy)3]2+ and [Co(terpy)2]2+ (bpy = 2,2'-bipyridine, terpy = 2,2':6',2″-terpyridine) presenting and discussing results from magnetic susceptibility measurements, X-ray crystallography, optical spectroscopy, and EPR spectroscopy
The compound of stoichiometry Mn(II)3[Mn(III)(CN)6]2.zH2O (z = 12-16) (1) forms air-stable, transparent red crystals. Low-temperature single crystal optical spectroscopy and single crystal X-ray diffraction provide compelling evidence for N-bonded high-spin manganese(II), and C-bonded low-spin manganese(III) ions arranged in a disordered, face-centered cubic lattice analogous to that of Prussian Blue. X-ray and neutron diffraction show structured diffuse scattering indicative of partially correlated (rather than random) substitutions of [Mn(III)(CN)6] ions by (H2O)6 clusters. Magnetic susceptibility measurements and elastic neutron scattering experiments indicate a ferrimagnetic structure below the critical temperature Tc = 35.5 K.
A new tetrathiafulvalene derivative 1 bearing a single pyridine group and its coordination complex 2, with stoichiometry [Mn(mu-Cl)Cl(1)2(CH3OH)]n, have been synthesized and fully characterized. The complex 2 shows an extended chain structure, which is potentially favorable for electrical conductivity. Notably, this is the first monohalogen-bridged Mn(II) polymer exhibiting a moderate antiferromagnetic coupling between the Mn(II) centers.
The ligand 1,2-bis(benzimidazol-2-yl)-1,2-ethanediol (H2bzimed, 1) and its N-methylated analogue (H2mbzimed, 2) form a variety of polynuclear complexes with copper(II), all of which contain a planar Cu2O2 lozenge as a central element and in which the bridging oxygen belongs to an alkoxo group of the ligand. Syntheses are reported for dinuclear [Cu2(Hmbzimed)2](ClO4)2 x 1.5H2O, Cu(2)2(2), and the tetranuclear species [Cu4(Hbzimed)4(ClO4)2](NO3)2 x 4H2O, Cu(4)1(4), [Cu4(Hmbzimed)2(mbzimed)Cl2](ClO4)2 x 2H2O x C2H5OH, Cu(4)2(3), and rac-[Cu4(H2bzimed)4(bzimed)(ClO4)2](ClO4)4 x 1.5H2O x 3.5C2H5OH, Cu(4)1(5). Crystal structures are reported for the tetranuclear species. Cu(4)1(4) shows a cubane structure, Cu(4)2(3) a stepped cubane structure, and rac-Cu(4)1(5) a novel structure in which one doubly deprotonated ligand lies between the two Cu2O2 units. Magnetic susceptibility measurements indicate that all complexes show antiferromagnetic coupling in the solid state. Studies in solution (ESI-MS, CD, NMR) show that Cu(2)2(2) and Cu(4)2(3) persist in solution but that Cu(4)1(4) dissociates partially and rac-Cu(4)1(5) completely. The six coordination modes of the ligands are discussed together with the effect of the N-methylation on the ligand conformation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.