Rüdiger Werner

Synthesis, reactivity and magnetochemical studies on copper(II) complexes derived from N-salicylidenearoylhydrazines. X-ray structure of [mononitratoOO( -1) (N-salicylidenatobenzoylhydrazine) - ONO( -1)]copper(II) monohydrate

Abstract A series of new mononuclear and binuclear copper(II) complexes derived from N-salicylidenearoylhydrazines (H2L) of the types K2[{Cu(L)(OH)}2]·nH2O, [Cu(HL)Cl·H2O]·nH2O, [{Cu(HL)Cl}2], [Cu(HL)NO2]·H2O, [{Cu(HL)}2]·2NO3, [{Cu(HL)H2O}2]·2NO3·nH2O and [Cu(HL)NCS]·H2O have been prepared and characterized. The X-ray crystal and molecular structure of [Cu(HSBzh)NO3]·H2O, where HSBzh refers to the mononegative N-salicylidenebenzoylhydrazine anion, has been determined. The complex is monomeric with the copper(II) adopting a (4+1) distorted square pyramidal coordination, with the ONO aroylhydrazone tridentate anion and an oxygen atom of the unsymmetric bidentate nitrate ion occupying the basal plane. The fifth coordination site is occupied by the other oxygen of the nitrate ion. The magnetic susceptibilities of both mononuclear and binuclear complexes were measured within the temperature range 4.2–298 K. All binuclear copper(II) complexes show strong antiferromagnetic interactions, and the singlet–triplet separation (−2J) recorded for μ-dihydroxy bridged complexes K2[{Cu(L)OH}2}]·nH2O are within the range 172–276 cm−1, while (−2J) for binuclear complexes [{Cu(HL)Cl}2], [{Cu(HL)}2]·2NO3 and [{Cu(HL)H2O}2]·2NO3·nH2O are respectively within the range 400–460, ca. 340 and ca. 390 cm−1. There are no appreciable exchange interactions between copper(II) ions in the monomeric complexes [Cu(HL)Cl·H2O]·nH2O, [Cu(HL)NO2]·H2O and [Cu(HL)NCS]·H2O. The IR spectra of the prepared complexes are also discussed.

Synthesis, magnetochemical studies and X-ray molecular structures of some mononuclear copper(II)–1H-pyrazole adducts and mono(μ-pyrazolate) bridged dicopper(II) complexes derived from N-salicylidenearoylhydrazines

Abstract 1H-Pyrazole complexes, [Cu(HL)HPz Cl] nH2O and [Cu(L)HPz] nH2O were prepared and characterized, where HL and L, respectively, refer to the mononegative and dinegative N-salicylidenearoylhydrazine anions. The X-ray crystal and molecular structure of [monochloro(N-salicylidenebenzoylhydrazinato)ONO(−1)monopyrazole] copper(II) monohydrate, [Cu(HSBzh)HPz Cl] H2O, and [(N-salicylidenebenzoylhydrazinato)ONO(−2)monopyrazole] copper(II) hemihydrate, [Cu(SBzh)HPz] 1/2H2O, were determined. The Cu(II) in [Cu(HSBzh)HPz Cl] H2O is in a distorted square pyramidal environment and is bound in the equatorial plane with the mononegative tridentate aroylhydrazone anion and pyrazole nitrogen, the axial fifth coordination site is occupied by a chloride ion. On the other hand, the complex [Cu(SBzh)HPz] 1/2H2O consists of two monomeric crystallographically independent but chemically similar molecules. In each molecule, the Cu(II) is in a distorted square planar geometry and is coordinated to the dinegative tridentate aroylhydrazone via the phenoxy oxygen, azomethine nitrogen and enolimide oxygen, and the fourth coordination site is occupied by the pyrazole nitrogen. The mono(μ-pyrazolate) dicopper(II) complexes, K[Cu2(L)2Pz] nH2O, were also prepared and the X-ray molecular structure of K2[Cu4(SBzh)4(Pz)2] 2H2O 1/2CH3OH was determined. In this complex, two copper(II) atoms are bridged by only one pyrazolate anion forming a dicopper mono(μ-pyrazolate) unit. Each two units are connected together by a five coordinate K+ cation forming a tetranuclear assembly. These tetranuclear assemblies are connected together by another K+ cation forming a supramolecular structure. Variable temperature magnetic studies on these pyrazolate complexes indicated antiferromagnetic behaviour with −2J values varying from 25 to 36 cm−1.

From Tetranuclear µ4‐Oxo to µ4‐Peroxocopper(II) Complexes

The unique properties of a newfamily of peroxocopper(II) complexes are discussed. They are stable at room temperature and contain the µ4-peroxo structural unit (right). Their synthesis, structure, and spectroscopic and magnetic properties are described.

Synthesis, characterization and magnetochemical studies of some imidazole and imidazolate copper(II) ternary complexes derived from N-salicylidenearoylhydrazines. X-ray crystal and molecular structures of [(N-salicylidene-p-chlorobenzoylhydrazine)ONO(−2)imidazole]copper(II) monohydrate and dimeric [(N-salicylidene-p-methylbenzoylhydrazine)ONO(−2)imidazole]copper(II) hemihydrate

Abstract The reactions of imidazole (Him) with N-salicylidenearoylhydrazine copper(II) complexes have been studied and a number of ternary copper(II) complexes, [Cu(L)Him]·nH2O, [Cu(HL)X·Him]·nH2O and [{Cu(L)}2Im]·nH2O, have been prepared and characterized (HL and L refer, respectively, to mono- and dinegative N-salicylidenearoylhydrazine anions and X is a mononegative monodentate ligand). The X-ray crystal and molecular structure of [(N-salicylidene-p-chlorobenzoylhydrazine)imidazole]copper(II) monohydrate, [Cu(Sp-ClBzh)Him]·H2O, and [(N-salicylidene-p-methylbenzoylhydrazine)imidazole]copper(II) hemihydrate, [Cu(Sp-CH3Bzh)Him]·1/2H2O, were measured. The p-chloro complex [Cu(Sp-ClBzh)Him]·H2O is monomeric with the Cu(II) in a distorted square planar environment and is coordinated to the tridentate hydrazone via phenoxy oxygen, azomethine nitrogen and enolimide oxygen, the fourth coordination site is occupied by the imidazole nitrogen. The p-methyl complex [Cu(Sp-CH3Bzh)Him]·1/2H2O was found to be a centrosymmetric dimer, the monomeric unit being bridged through the phenoxy oxygen. The Cu(II) is in a square pyramidal environment and is bounded in the equatorial plane with the enolimide oxygen, azomethine nitrogen and phenoxy oxygen of the hydrazone ligand while the fourth site is occupied by the symmetry related phenoxy oxygen of the other unit; the axial fifth coordination site is occupied by the imidazole nitrogen. The magnetic susceptibility measurements at different temperatures (5–298 K) have been recorded and are discussed. The binuclear imidazolate complexes show antiferromagnetic exchange coupling interactions, the measured −J values are within the range 17.0–20.0 cm−1, while the imidazole complexes do not show any appreciable exchange interactions.

Crystal structure and spin crossover studies on bis(2,6-bis(benzimidazol-2-yl)pyridine) iron(II) perchlorate

Abstract The structure of the [Fe(bzimpy) 2 ](ClO 4 ) 2 · x H 2 O system ( x = 0.25) was determined by single crystal X-ray structure analysis. The Fe(II) ion is hexacoordinated by six donor nitrogen atoms. The magnetic properties of the complex were investigated by powder magnetic susceptibility measurements and ESR. The freshly prepared sample does not show any traces of iron(III) impurities but these are formed as a function of time. After 1 year the sample contains 8.2% iron(III) as shown by UV spectroscopy and indicated by g eff = 4.3 and 2.0 in its ESR spectrum. This explains the recorded ξ versus T behaviour at low temperature: with increasing temperature the ξ value decreases according to the Curie-Weiss law for a S = 5/2 system having an effective g = 4.3. Above 220 K a continuous increase in the ξ value is observed and a spin crossover applies. The spin transition is not complete at room temperature. A pronounced hysteresis is observed upon heating/cooling the sample between 220 and 414 K on the basis of magnetic data and infrared spectra.

Synthesis, characterization and magnetochemical studies of dicopper(II) complexes derived from bis(N-salicylidene)dicarboxylic acid dihydrazides

Two series of dicopper(II) complexes derived from bis(N-salicylidine)dicarboxylic acid dihydrazides (H4L n ) of general formula [Cu2(L n )·xH2O]·yH2O and [Cu2(H2L n )Cl2·xH2O]·yH2O have been synthesized and characterized, where n refers to the number of carbon atoms in the aliphatic spacer between the two N-salicylideneacylhydrazine units. Magnetic susceptibility measurements for neutral dicopper(II) complexes [Cu2(L n )·xH2O]·yH2O indicate significant antiferromagnetic coupling between copper(II) centers. The −2J values obtained from the Bleany–Bowers equation are within the range 121–223 cm−1, suggesting association of the coordinated copper(II) units Cu(ONO) via phenoxy bridges. This leads to a polynuclear structure in which the dimeric units are connected with the aliphatic spacer. From the best-fit values of the mole fraction of paramagnetic uncoupled copper(II) centers (ρ), the degree of association in these polynuclear copper(II) complexes has been estimated. The chloro dicopper(II) complexes [Cu2(H2L n )Cl2·xH2O]·yH2O with n = 0, 2 and 3 also show strong antiferromagnetic exchange coupling (−2J = 215–423 cm−1), suggesting a polynuclear structure in which the copper(II) is in a distorted square-pyramidal environment, bound in the equatorial plane with a monoanionic ONO tridentate acylhydrazone unit and the μ-phenoxy oxygen and the axial site occupied by a chloride. The dicopper(II) complexes with n = 1 and 4 show weak antiferromagnetic exchange coupling (−2J = 16–20 cm−1). In these complexes the chloride ion may occupy the fourth equatorial site while the μ-phenoxy is in the apical position.

Magnetic properties of dinuclear cobalt complexes

We report the magnetic investigation of dinuclear Co(II) compounds on the base of hamiltonian which takes into account exchange interaction, zero-field splitting and Zeeman perturbation. The treatment of this hamiltonian is performed with the use of the irreducible tensor operator technique and symmetry of the system. A good agreement of the experimentally observed magnetic susceptibility and the results of calculation is obtained.

Metal Complexes Derived from Hydrazoneoxime Ligands: I. Synthesis, Characterization and Magnetochemical Studies of (Acylhydrazoneoxime) Copper(II) Complexes

Reactions of 2-hydroxyimino-1-methylpropylidene (acetyl-) and (benzoylhydrazine) with copper(II) chloride, nitrate and acetate were studied. Three types of copper(II) complexes of general formula [Cu(H2L)Cl2], [{Cu(HL)}2]⋅2NO3⋅nH2O and [{Cu(L)}2], where H2L, HL, and L refer, respectively, to the neutral, monoanionic and dianionic ONN tridentate acylhydrazoneoxime ligands, were isolated and characterized. Variable-temperature magnetic susceptibility measurements for [Cu(H2L)Cl2] suggest Curie-Weiss behavior. Both [{Cu(HL)}2]⋅2NO3⋅nH2O and [{Cu(L)}2] show strong antiferromagnetic exchange coupling with − 2J values of 898-934 and 718-757 cm−1, respectively, indication dimeric structures with oximate bridges.

A new dinucleating N,O donor ligand (H2BPClNOL) and the structural and magnetic properties of two diiron complexes with the di-m-alkoxo motif

Dois complexos binucleares de FeIII, obtidos a partir de um novo ligante polidentado (H2BPClNOL =N-(2-hidroxibenzil)-N-(2-piridilmetil)[(3-cloro)(2-hidroxi)] propilamina e contendo a unidade estrutural FeIII(m-alcoxo)2FeIII, foram caracterizados estruturalmente atraves de estudos cristalograficos e magneto-quimicos. Os complexos [Fe2(BPClNOL)2(OAc)]ClO4 (1) [Fe2(BPClNOL)2(H2O)2](ClO4)2. 4H2O (2) diferem entre si pela presenca de um grupo acetato em ponte entre os sitios de FeIII no complexo (1). O complexo contendo a ponte acetato apresenta constante de acoplamento antiferromagnetico aproximadamente 20 % menor quando comparado ao complexo sem ponte acetato.

Electron localization–delocalization in mixed-valence iron dimers

Two mixed-valence iron dimers, [L1Fe2(μ-OAc)2](ClO4) and [L1Fe2(μ-OBz)(OBz)(H2O)](ClO4), were investigated. The temperature dependence of the effective magnetic moments and the position and shape of the intervalence absorption bands were calculated using a Hamiltonian taking into account isotropic exchange interaction, double exchange, Zeeman interaction, zero-field splitting for the ground state and vibronic coupling with the PKS out-of-phase mode. The similarities and differences of the investigated compounds were explained on the basis of analysis of the adiabatic potentials. The behaviour of both systems is determined by a strong competition between two main processes: double exchange interaction and vibronic coupling with PKS out-of-phase mode. Degree of delocalization of the itinerant extra electron was calculated at different values of temperature.