Ionophoric binding of alkaline-earth-metal cations (A<SUP>2+</SUP>) by tris(arylazo oximato)iron(II) anions (RL<SUP>-</SUP>): the trinuclear A(RL)<SUB>2</SUB> family

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Cobalt(II) and cobalt(III) complexes with N -(aroyl)-N' -(picolinylidene)hydrazines. Spin -crossover in the cobalt(II) complexes

2352-2358Complexes of cobaIt(II) and cobaIt(III) with tridentate N-(aroyl)-N'-(picolinylidene)-hydrazines (HL, H stands for the dissociable amide proton) are described. The Schiff bases (HL) have been obtained by condensation of 2-pyridinecarboxaldehyde with benzhydrazide or 4-substituted benzhydrazides. The reactions of Co(O2CCH3)2.4H2O and HL at room temperature under aerobic condition afford the complexes with general formulae [CoIIL2] (-Cl and -NO2 as substituents) and [COIIIL2]+(-H, -CH3, -OCH3 and -N(CH3)2 as substituents). The cationic complexes have been isolated as PF6- salts. Analytical, spectroscopic, magnetic and electrochemical techniques have been used for the characterization of these complexes. X-ray structure of [Co(pamh)2]PF6 has been determined. In each complex, the metal centre is in N4O2 coordination sphere constituted by the meridionally spanning pyridine-N, imine-N and deprotonated amide-O donor ligands. Infrared spectra are consistent with the enolate form of the amide functionalities in both ligands. Cobalt(III) complexes,[CoL2]PF6, are diamagnetic and NMR active. In acetonitrile solutions the complexes behave as 1:1 electrolyte. Electronic spectra of the complexes display charge transfer bands in the range 453-221 nm. All the complexes are redox active and display the Co(III)-Co(II) couple in the potential range -0.23 to +0.09 V (vs. Ag/AgCl). The trend in these potential values reflects the effect of the electronic nature of the substituents on the aroyl moiety of the ligands. Cobalt (II) complexes,[CoL2], are paramagnetic and electrically nonconducting in solutions. Variable temperature magnetic susceptibility measurements and EPR spectra reveal S = 3/2 ↔ S = 1/2 spin-crossover in both cobalt(II) complexes

First example of a mixed-spin trinuclear manganese(II) complex: [MnN6(S =&#189;)][MnO<SUB>6</SUB>(S = 5/2)][MnN<SUB>6</SUB>(S = &#189; )]

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Manganese(IV) in discrete O<SUB>3</SUB>S<SUB>3</SUB> coordination

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Chemistry of ferroverdin: trinuclear species of type [M(FeL₃)₂](M = Mg, Ca, Mn, Fe, Co, Ni, Zn, or Cd; L = 4-methyl-1,2-benzoquinone 2-oximate)

Reaction of sodium tris (4-methyl-1,2-benzoquinone 2-oximato) ferrate(II), Na[FeL3], with M2+(M = Mg, Ca, Mn, Fe, Co, Ni, Zn, or Cd) in methanol furnishes trinuclear species of type [M(FeL3)2]. Upon treatment with NaOH, M(OH)2 is precipitated and Na[FeL3] is regenerated. The iron(II) atoms of the two [FeL3]– moieties in the trinuclear complexes are low spin but M2+ is high spin (S=5//2, 2, 3/2, and 1 in the cases of M = Mn, Fe, Co, and Ni respectively). The M2+ site can be doped with Mn2+ and e.s.r. data for the doped complexes are compatible with a near octahedral environment of the M2+ site. It is proposed that this environment is created by the six oximato oxygen atoms of the two facial [FeL3]– moieties. The significance of the present work in relation to the reported variation of the iron content in different preparations of ferroverdin is noted

Synthesis and structure of a trinuclear manganese(II) complex containing low-spin metal

The reaction of α-phenylazobenzaldehyde oxime, HL, with manganese(II) salts has afforded the first known mixed-spin trinuclear complex [Mn^II₃L₆]. The structure of the benzene solvate [Mn₃L₆]·2C₆H₆ has been determined by X-ray crystallography. The Mn₃ fragment is exactly linear with the terminal low-spin (S=½) metal(II) atoms tris-chelated by azo- and oxime-nitrogen functions into facial pseudo-octahedral MnN6 dispositions. Two such [MnL₃]^– moieties sequester the central high-spin (S=5//2) manganese(II) atom into an O₆ environment using oximato oxygen donors. The average Mn···Mn, Mn–N, and Mn–O distances are 3.577(7), 1.956(18), and 2.146(15)Å respectively. It is proposed that oximato nitrogen co-ordination is primarily responsible for the low-spin configuration of the terminal manganese(II) atoms