Masayuki Koikawa

Binuclear copper(II) complexes of new dinucleating ligands with a pyrazolate group as an endogenous bridge. Effects of exogenous azide and acetate bridges on magnetic properties

New dinucleating ligands containing pyrazole as an endogenous bridging group, 3,5-bis-[N-(2-pyridylmethyl)carbamoyl] pyrazole (H3L1), 3,5-bis{N-[2-(diethylamino)ethyl]carbamoyl}pyrazole (H3L2), and 3,5-bis{N-[3-(dimethylamino)propyl]carbamoyl}pyrazole (H3L3), and their binuclear copper(II) complexes with azide or acetate ion as an exogenous bridge, [CU2L(N3)(H2O)2]·H2O(L = L1–L3) and [Cu2L1(O2CMe)]·2MeOH, have been obtained. Cryomagnetic investigations (5–300 K) reveal a significant antiferromagnetic spin exchange for the azide-bridged complexes(–J= 371–297 cm–1), but a ferromagnetic spin exchange (J > +8.9 cm–1) for the acetate-bridged complex. The azide-bridged complexes are e.s.r. silent. The acetate-bridged complex is unstable in dimethylformamide (dmf) but a quickly prepared dmf frozen solution of the sample gives X-band signals characteristic of a spin-triplet (S= 1) state, together with signals due to a spin doublet(S=½) attributable to monomeric copper(II). Signals at 812, 1 292, and 4 380 G show a seven-line hyperfine structure (Azz= 0.0103 cm–1); the first and third signals are assigned to ΔMs= 1 transitions and the second to the ΔMs= 2 transition of the parallel resonance of the spin-triplet state. E.s.r. simulation based on the spin Hamiltonian for the spin triplet of a dicopper(II) system gives gzz= 2.533, D= 0.210 cm–1, and E= 0.020 cm–1. Only two components of the perpendicular resonances are recognizable at 2 113 and 3 812 G which give gx= 2.055.

Template synthesis, structure and characterization of NiII2PbII and CuII2PbII complexes of macrocycles with a N4O2 donor set

The reaction of [N,N′-ethylene- or [N,N′-propane-1,3-diylbis(3-formyl-5-methylsalicylideneiminato)]-metal(II)(M = Cu or Ni) and a diamine (ethylenediamine, propane-1,3-diamine, butane-1,4-diamine or pentane-1,5-diamine) in the presence of lead(II) ion gives macrocyclic complexes [Pb(MLm,n)2]X2[H2Lm,n= macrocycle formed by the condensation of two molecules of 2,6-diformyl-4-methylphenol and two diamines H2N(CH2)mNH2 and H2N(CH2)nNH2; m= 2 or 3 and n= 2–5; M = Cu or Ni; X = CIO4, PF6, BPh4 or BF4]. They were characterized by elemental analyses, single-crystal X-ray analysis, fast atom bombardment mass, IR, electronic and ESR spectra and magnetic measurements. The crystal structure of [Pb(CuL3,3)2][CIO4]2 has revealed that the copper(II) ion in each CuL3,3 is bound at one of the N2O2 donor sites and the lead ion is sandwiched by the vacant N2O2 sites of two CuL3,3 entities, providing a square-antiprismatic environment.

Binuclear copper(II) complexes bridged by oxamidate and dithio-oxamidate groups. Synthesis, structure, and magnetism

Binuclear copper(II) complexes bridged by oxamidate (oxd) or dithio-oxamidate (dto) groups [Cu2L2(oxd)]X2 and [Cu2L2(dto)]X2[L = 2,2′-bipyridyl (bipy) or 1,10-phenanthroline, X = NO3 or ClO4], have been synthesized. Single-crystal X-ray analysis for [Cu2(bipy)2(oxd)][ClO4]2·2dmf (dmf = dimethylformamide) reveals that the oxd2– ion in trans conformation bridges two copper(II) ions with an intermetal distance of 5.192(2)A. The configuration around each copper is square pyramidal with two nitrogens of bipy and one nitrogen and one oxygen of oxd in the basal plane and a perchlorate oxygen at the apex [2.433(9)A]. The dto-bridged complexes are characterized by two intense i.r. bands at 1 540 and 1 440 cm–1 and a charge-transfer band at (21.6–21.9)× 103 cm–1. Magnetic analyses in the temperature range 80–300 K on the basis of the Bleaney–Bowers equation gave –2J values (singlet–triplet energy separation) of 488–566 cm–1 for the oxd-bridged complexes and 726–982 cm–1 for the dto-bridged complexes, indicating that the dithio-oxamidate bridge mediates a stronger antiferromagnetic spin exchange between copper(II) ions than does the oxamidate bridge. Cyclic voltammograms for the oxd complexes show an irreversible couple at +0.1 V vs. the saturated calomel electrode which is assigned to the process CuII2→ CuICuII.

Synthesis, structure, and redox properties of dicopper(II,II) complexes of N-(2-hydroxyphenyl)salicylamide and homologues. Facile oxidation to dicopper-(II,III) and -(III,III) species; crystal structure of bis(tetrabutylphosphonium) bis{[(2-oxidobenzoyl)(2′-oxidophenyl)amido(3–)-NO2,µ-O2′]cuprate(II)}

Binuclear copper (II) complexes of N-(2- hydroxyphenyl)salicylamide (H3L1) and its homologues with a substituent on the ‘2-hydroxyphenyl’ moiety (5-Me, H3L2; 5-Cl, H3L3; 5-NO2, H3L4) have been obtained as tetrabutylphosphonium salts [PBu4]2[CU2L2]. The structure of [ PBu4]2[Cu2L12] was solved by single-crystal X-ray crystallography, which demonstrated that two copper ions are bridged by the phenolic oxygen of the ‘aminophenol’ moiety with a Cu ⋯ Cu separation of 3.035(2)A. Each copper ion adopts an essentially planar configuration, and the Cu–O and Cu–N bond distances involving the salicylamide moiety are relatively short [1.838(6) and 1.915(6)A respectively]. Cryomagnetic investigations (80–300 K) revealed a significant antiferromagnetic spin exchange though the bridging oxygen, the 2J value (energy separation between the spin singlet and triplet states) being –393.4 to –448.8 cm–1. The cyclic voltammogram of each complex showed two oxidation waves attributable to Cu2II,III–Cu2II,III and Cu2II,III–Cu2III,III processes at significantly low potentials. The dicopper(II,III) species of the L2 complex was generated by electrochemical and chemical (with Br2) oxidation and identified by e.s.r. investigations. The mixed-valence complex in dichloromethane showed an e.s.r. signal with a four-line hyperfine structure (Aav. = 79 ×10–4cm–1) at g= 2.10 at room temperature, indicating that the unpaired electron is localized on one of the copper ions on the e.s.r. time-scale. The mixed-valence complexes each showed an intense absorption in the visible region which is tentatively assigned to the intervalence transitions.

Synthesis and characterization of iron(III) and iron(IV) complexes of N-(2-hydroxyphenyl)salicylamide and homologs

The complexation of tridentate trianionic chelating ligands, N-(2-hydroxyphenyl)salicylamide (H3L1) and its homologs with a substituent on the 2-hydroxyphenyl moiety (5-CH3, H3L2; 5-Cl, H3L3), toward iron ion has been studied. The ligand H3L1 formed a high-spin iron(III) complex K3[Fe(L1)2] when treated with FeCl3 in an alkaline solution under open atmosphere. This complex was oxidized with Ce(IV) to a high-spin iron(IV) complex (NPr4)2[Fe(L1)2]. The ligand H3L2 formed a low-spin iron(IV) complex K2[Fe(L2)2] under open atmosphere, whereas the ligand H3L3 gave a high-spin iron(III) complex (PBu4)3[Fe(L3)2]. The complexes were characterized by means of cyclic voltammetry, electronic spectra and Mossbauer spectra.

Reaction of 3,5-di-t-butyl-o-benzoquinone on Co(II)M(III) (M=Y, La) heterodinuclear centres: The formation and ESR spectra of Co(III)M(III)-semiquinone adducts

Abstract The reactions of 3,5-di-t-butyl- o -benzoquinone (DBQ) with the Co(II)M(III) (M=Y, La) complexes of N,N′ -bis(3-carboxysalicylidene)ethylenediamine have been studied in dmf solutions by means of ESR spectroscopy. The ESR spectral study has shown that DBQ oxidizes the Co(II) ion of the Co(II)M(III) complexes to afford a Co(III)M(III)-DBSQ species (DBSQ=semiquinone form of DBQ) but the DBSQ is bound to the M(III) ion but not to the Co(III). The reaction of the mononuclear cobalt(II) complex [Co(H 2 L)] with DBQ afforded [Co(H 2 L)(DBSQ)] where DBSQ coordinates to the cobalt(III) ion as a bidentate chelate.

Cobalt(II) and μ-oxodiiron(III, IV) complexes of salen analog with aromatic thioether pendant group, N,N'-disalicylidene-2-methyl-4-(2-methylthiophenyl)-1,2-butanediamine

Abstract A pentadentate salen analog containing a thioether group in the pendant tail, N , N ′-disalicylidene-2- methyl-4-(2-methylthiophenyl)- 1,2-butanediamine, has been synthesized. The cobalt(II) complex of this ligand retains a planar configuration free from the coordination of the pendant group at room temperature but adopts a square-pyramidal configuration with the thioether at the apex near liquid nitrogen temperature. The iron complex obtained with this ligand is shown to be a μ-oxodiiron(III, IV) complex comprised of high-spin iron(III) and low-spin iron(IV), based on cryomagnetic data (80–300 K), ESR, and M:ossbauer spectra. An antiferromagnetic spin-exchange interaction ( J = − 13.0 cm −1 ) operates between the metal ions.

Nickel(II) and Palladium(II) Complexes of N-(2-Hydroxyphenyl)Salicylamides. Synthesis, Structure, and Electrochemical Properties

Abstract N-(2-Hydroxyphenyl)salicylamide (H3L1) and N-(2-hydroxy-5-chlorophenyl)salicylamide (H3L2) formed diamagnetic nickel(II) and palladium(II) complexes of the composition (PBu4)2[M(L)(H2L)] (PBu4 + = tetrabutylphosphonium ion; M = Ni, Pd; L = L1, L2). Single-crystal X-ray analysis for (PBu4)2[Pd(L1)(H2L1)] revealed that one ligand (L1)3-coordinates terdentately and the other ligand (H2L1)-coordinates unidentately at the phenolic oxygen of the “salicylamide” entity, affording a planar configuration around the metal ion. In cyclic voltammograms both Ni and Pd complexes showed one oxidation wave attributable to the process M(II)/M(III) at a significantly low potential. The Ni(III) and Pd(III) species of the L2 complex were generated by electrochemical oxidation and identified by electronic absorption and ESR spectra. Based on electronic absorption and ESR spectra, a considerable delocalization of the unpaired electron onto the ligand orbitals was suggested for both Ni(III) and Pd(III) complexes.