Light-induced excited spin state trapping and charge transfer in trigonal bipyramidal cyanide-bridged complexes

Three members of the family of trigonal bipyramidal (TBP) complexes of general formula [M(tmphen)(2)](3)[M'(CN)(6)](2) (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) or [M(3)M'(2)], which are known to exhibit thermally induced spin crossover and charge transfer, have been investigated for optical and photomagnetic properties. The light-induced excited spin-state trapping (LIESST) effect found in classical spin crossover compounds, such as [Fe(phen)(2)(NCS)(2)], was explored for the [Fe(3)Fe(2)] and [Fe(3)Co(2)] compounds. Similarly, inspired by the light-induced charge-transfer properties of K(0.2)Co(1.4)[Fe(CN)(6)]·6.9H(2)O and related Prussian blue materials, the possibility of photo-induced magnetic changes was investigated for the [Co(3)Fe(2)] TBP complex. Optical reflectivity and magnetic susceptibility measurements were used to evaluate the photoactivity of these compounds. A comparison of these data before and after light irradiation demonstrates that (i) the spin crossover of the Fe(II) centers in the [Fe(3)Fe(2)] and [Fe(3)Co(2)] analogues and the (ii) charge transfer events in the [Co(3)Fe(2)] complex occur with temperature and irradiation. In addition, photomagnetic behavior is exhibited by all three compounds. The photo-conversion efficiency has been estimated at 20% of photo-induced high spin Fe(II) centers in [Fe(3)Co(2)], 30% of paramagnetic Co(II)-Fe(III) pairs in [Co(3)Fe(2)], and less than 2% of photo-induced high spin Fe(II) centers in [Fe(3)Fe(2)].     

Molecular magnetic materials based on 4d and 5d transition metals

The study of paramagnetic compounds based on 4d and 5d transition metals is an emerging research topic in the field of molecular magnetism. An essential driving force for the interest in this area is the fact that heavier metal ions introduce important attributes to the physical properties of paramagnetic compounds. Among the attractive characteristics of heavier elements vis-à-vis magnetism are the diffuse nature of their d orbitals, their strong magnetic anisotropy owing to enhanced spin-orbit coupling, and their diverse structural and redox properties. This critical review is intended to introduce readers to the topic and to report recent progress in this area. It is not fully comprehensive in scope although we strived to include all relevant topics and a large subset of references in the area. Herein we provide a survey of the history and current status of research that has been conducted on the topic of second and third row transition metal molecular magnetism. The article is organized according to the nature of the precursor building blocks with special topics being highlighted as illustrations of the special role of heavier transition metal ions in the field. This paper is addressed to readers who are interested in molecular magnetism and the application of coordination chemistry principles to materials synthesis (231 references).     

catena‐Poly­[[di­aqua­cobalt(II)]‐μ‐oxalato]

Single crystals of the title compound, [Co(C₂O₄)(H₂O)₂]_n, have been prepared by hydro­thermal methods and characterized by X‐ray diffraction analysis. The crystal structure consists of infinite one‐dimensional chains of di­aqua­cobalt(II) units bridged by oxalate groups. These chains lie on twofold symmetry axes parallel to the b axis, and the [Co(C₂O₄)]_n system is nearly planar within experimental error. The cobalt(II) coordination polyhedra are irregular octahedra, with oxalate O atoms at the equatorial positions and water mol­ecules at the axial positions. The chains are linked by hydrogen bonds via the water mol­ecules.     

Study of collisional relaxation of ions by two-photon photodissociation

Collisional relaxation of bromobenzene molecular ion by several neutral molecules has been measured by a two-photon photodissociation method. This new technique allows a quantitative estimation of energy loss in the relaxation process. Collisional relaxation rates have been found to be much slower than expected from orbiting collision rates.     

铸造铝青铜合金Cu-14Al-4Fe-Mn的摩擦磨损性能

用往复式摩擦磨损试验机考察了新型高强度、高耐磨性铸造铝青铜合金Cu-14Al-4Fe-Mn(代号HSWAB)的摩擦磨损性能,利用形貌扫描电子显微镜观察分析了合金磨损表面形貌,探讨了其磨损机理.结果表明,HSWAB合金在干摩擦和油润滑条件下的摩擦磨损性能及磨损机理存在明显差异.在干摩擦条件下,合金中脱落的硬质点及氧化物等磨粒导致较为严重的磨粒磨损,摩擦系数高、磨损率大,主要磨损机理为磨粒磨损、粘着磨损、氧化磨损及疲劳磨损.在油润滑条件下,摩擦系数和磨损率均显著降低,疲劳磨损和氧化磨损受到抑制,主要磨损机理为磨粒磨损和粘着磨损.Cu-14Al-4Fe-Mn合金在油润滑条件下的摩擦系数低达0.08,磨损率低达3.7×10-6g/m,是一种优良的耐磨材料.