Search results for "transition metal ion"

Komplexierung von Übergangsmetall-Ionen mit substituierten Azamakrocyclen: Induktion columnarer Mesophasen durch molekulare Erkennung

1991

Spin Crossover – Quo Vadis?

2013

This retrospective essay is an attempt to span the bridge over eight decades of research on spin crossover (SCO), one of the most fascinating dynamic electron structure phenomena of inorganic coordination chemistry. The occurrence of SCO compounds of 3d transition metal ions and their characterization regarding magnetic, optical, vibrational, structural, and thermodynamic properties are briefly addressed. Selected case studies of chemical influences and physical effects (pressure, magnetic field, light) on SCO behavior are discussed. Particular attention is paid to the importance of Mossbauer spectroscopy in SCO studies. Light-induced excited spin state trapping (LIESST) and related photoph…

Reversible Colorimetric Probes for Mercury Sensing

2005

The selectivity and sensitivity of two colorimetric sensors based on the ruthenium complexes N719 [bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) bis(tetrabutylammonium) bis(thiocyanate)] and N749 [(2,2':6',2' '-terpyridine-4,4',4' '-tricarboxylate)ruthenium(II) tris(tetrabutylammonium) tris(isothiocyanate)] are described. It was found that mercury ions coordinate reversibly to the sulfur atom of the dyes' NCS groups. This interaction induces a color change in the dyes at submicromolar concentrations of mercury. Furthermore, the color change of these dyes is selective for mercury(II) when compared with other ions such as lead(II), cadmium(II), zinc(II), or iron(II). The detection limit…

A Vanadium(III) Complex with Blue and NIR-II Spin-Flip Luminescence in Solution.

2020

Luminescence from Earth-abundant metal ions in solution at room temperature is a very challenging objective due to the intrinsically weak ligand field splitting of first-row transition metal ions, which leads to efficient nonradiative deactivation via metal-centered states. Only a handful of 3d

A dinucleating ligand which promotes DNA cleavage with one and without a transition metal ion.

2013

The dinucleating ligand L (1,3-bis[bis(pyridin-2-ylmethyl)amino]propan-2-ol) combined with metal ions efficiently cleaves DNA when M : L is 1 : 1 (M = Co(II) or Fe(III)) at pH 5.5–7.0, with free L being more active at acidic pH than when bound to Zn(II), Cu(II) or Ni(II) at neutral pH.

Anisotropic double exchange in orbitally degenerate mixed valence systems

2000

Abstract The problem of the double exchange is considered for the mixed valence dimers in which one or both transition metal ions possess orbitally degenerate ground states. In the pseudo-angular momentum representation, the general formula is deduced for the matrix elements of double exchange involving the transfer integrals and all spin and orbital quantum numbers. The pairs 3 T 1 t 2 2 – 2 T 2 t 2 1 and 3 T 1 t 2 2 – 4 A 2 t 2 3 are considered in three high-symmetric topologies: edge-shared D2h, corner-shared D4h, and face-shared D3h bioctahedra. The double exchange in orbitally degenerate systems is shown to produce strong magnetic anisotropy of an orbital nature. The character of the a…

Aging and Memory Effects in PLZT 8/65/35 Ceramics Modified with 3d Transition-Metal Ions

2015

The temperature and frequency dependencies of the dielectric susceptibility in relaxor electro-optical PLZT 8/65/35 modified with 3d transition-metal ions (Mn, Fe, Co, Ni) measured to study the aging and memory effects are reported. The studies of aging at room temperature show that 3d admixtures (Me) in PLZT 8/65/35 ceramics at small to medium concentration range (Me < 1.0 wt.%) change the depth of dispersion, the aging amplitude and the temperature range of the memory effect. At admixture concentrations Me →1.0 wt% the aging and memory effect are significantly reduced (or eliminated).The obtained results suggest that aging effects are determined by two substantial acceptor effects of the …

A novel approach for obtaining α,β-diaminophosphonates bearing structurally diverse side chains and their interactions with transition metal ions stu…

2020

Aminophosphonates are an important group of building blocks in medicinal and pharmaceutical chemistry. Novel representatives of this class of compounds containing nontypical side chains are still needed. The aza-Michael-type addition of amines to phosphonodehydroalanine derivatives provides a simple and effective approach for synthesizing N′-substituted α,β-diaminoethylphosphonates and thus affords general access to aminophosphonates bearing structurally diverse side chains. Thermodynamic analysis of the chosen aminophosphonates at physiological pH proves that they serve as potent chelators for copper(II) ions and moderate chelators for nickel(II) ions.

Double Exchange in Orbitally Degenerate Mixed Valence Clusters: Magnetic Anisotropy, Vibronic Effects

2001

In this paper we consider the vibronic problem of the double exchange in mixed-valence dimers containing transition metal ions in orbitally degenerate ground states. The vibronic model includes interaction with the breathing local modes (Piepho-Krausz-Schatz-PKS) as well as the modulation of metal-metal distances as suggested by Piepho. The double exchange in orbitally degenerate systems is shown to produce strong magnetic anisotropy of orbital nature. PKS interaction is expected to suppress the magnetic anisotropy of the system, while the intercenter vibrations tend to enhance it. The roles of spin-orbit coupling and temperature are revealed for the systems with different geometries.

Magnetic Exchange between Orbitally Degenerate Ions:  A New Development for the Effective Hamiltonian

1998

A new approach to the problem of the kinetic exchange for orbitally degenerate ions is developed. The constituent multielectron metal ions are assumed to be octahedrally coordinated, and strong crystal field scheme is employed, making it possible to take full advantage from the symmetry properties of the fermionic operators and collective electronic states. In the framework of the microscopic approach, the highly anisotropic effective Hamiltonian of the kinetic exchange is constructed in terms of spin operators and standard orbital operators (matrices of the unit cubic irreducible tensors). As distinguished from previous considerations, the effective Hamiltonian is derived for a most genera…