A series of four-coordinate square-planar nickel(II) complexes of o-phenylenebis(N'-methyloxamidate)(L1) and related o-phenylene(N'-methyloxamidate)oxamate (L2) and o-phenylenebis(oxamate)(L3) tetradentate ligands have been synthesized and characterized structurally, spectroscopically and electrochemically. The parent nickel(II)-L1 complex presents an intense MLCT band in the UV region (lambda max = 357 nm) and a distinctive 1 s --> 4p CT satellite in the Ni K-edge XANES spectrum (E = 8339.2 eV). These features together with the short Ni-N(amidate) bond lengths (1.85-1.93 A) as revealed by the analysis of the Ni K-edge EXAFS spectrum and confirmed by single-crystal X-ray diffraction are typical of square-planar low spin (S = 0) Ni(II) ions. The dianionic nickel(II) complexes, [Ni(II)L(i)](2-)(i = -3), experience two redox processes in acetonitrile at 25 degrees C. The first redox process, at moderately low potentials (E1 = 0.12-0.52 V vs. SCE), is a reversible one-electron metal-centered oxidation to the corresponding monoanionic nickel(III) complexes, [Ni(III)L(i)]-. The second redox process, at relatively high potentials (E2 = 0.86-1.04 V vs. SCE), is a quasireversible to irreversible one-electron oxidation largely centered on the o-benzenediamidate fragment of the non-innocent ligand, yielding the corresponding neutral nickel(iii) complexes with a o-benzosemiquinonediimine pi-cation radical ligand, [Ni(III)(L(i))*+]. The singly and doubly oxidized species of the parent nickel(II)-L1 complex have been prepared by chemical oxidation and characterized spectroscopically in acetonitrile at -40 degrees C. The stable singly oxidized nickel(III)-L1 species presents an intense LMCT band in the NIR region (lambda max = 910 nm) and a rhombic X-band EPR spectrum (g1 = 2.193, g2 = 2.080 and g3 = 2.006) characteristic of square-planar low spin (S = 1/2) Ni(III) ions. The unstable double oxidized nickel(III)-L1 pi-cation radical species exhibits a rather intense visible band (lambda max = 645 nm) that is tentatively assigned as a MLCT transition from the Ni(III)-benzosemiquinone type ground state to the Ni(IV) excited state.

The new heterometallic sodium(I)-copper(II) compound Na4Cu2 (2) . 10.5 H2O (3), where H-8[2] stands for N,N',N ",N'''-methanetetrayltetrakismethylenetetrakis (oxamic acid), has been synthesized and its crystal structure determined by single-crystal X-ray diffraction. The structure of 3 consists of cationic [Cu-2(eta(4):eta(4)-2](4-) dinuclear units, coordinated sodium cations, and water molecules. In the crystal, the dinuclear copper entities are joined through discrete aggregates of eight sodium atoms linked by oxamato and water bridges, leading to a three-dimensional polymeric network.

Two new heterobimetallic complexes [Cu(pdmg)Ni(Me3[12]N3)(CH3CH2OH)](ClO4)2 (2) and [Cu(pdmg)Mn(bipy)2](ClO4)2 · H2O (3) (H2pdmg=3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioxime; Me3[12]N3=2,4,4-trimethyl-1,5,9-triazacyclododeca-1-ene; bipy=2,2′-bipyridyl) have been prepared and characterized. The structure of 2 has been determined by single-crystal X-ray diffraction methods. It consists of [Cu(pdmg)Ni(Me3[12]N3)(CH3CH2OH)]2+ cations and non-coordinated perchlorate anions. The [Cu(pdmg)(CH3CH2OH)] complex coordinates to the [Ni(Me3[12]N3)]2+ fragment to afford the binuclear unit doubly-bridged by oximato groups in cis arrangement. The coordination geometry around the copper atom is square-pyramidal, whereas the nickel atom exhibits a trigonal-bipyramidal surrounding. The intramolecular Cu–Ni distance is 3.810(6) Å. In the crystal, two [CuIINiII] dimeric units are related through an inversion center, giving rise to a bis-binuclear entity with a relatively short intermolecular Cu–Cu separation of 4.175(6) Å. Variable-temperature magnetic susceptibility measurements (2.0–300 K) for 2 correspond to an almost isolated Cu(II)Ni(II) pair with an intrapair interaction parameter J=−143.6(2) cm−1. However, the EPR spectrum at 4.2 K is that of a triplet spin state arising from the interaction between the two doublet spin states within the [CuIINiII]2 bis-binuclear entity. The magnetic properties of 3 unambiguously reveal the bis-binuclear nature of this compound, as is the case for the related homometallic complex [Cu(pdmg)Cu(bipy)(H2O)2](ClO4)2 · H2O (1). The intra- (J) and interpair (j) interaction parameters for 3, as deduced from the analysis of its magnetic susceptibility data in the temperature range 2.0–300 K, are −50.9(2) and 1.50(2) cm−1, respectively. The field dependence of the magnetization of 3 at 2.0 K corresponds to that of a nonet state arising from the interaction between two quintuplet spin states within the [CuIIMnII]2 bis-binuclear entity. The interaction between the heterobinuclear Cu(II)Mn(II) molecules and its influence on the nature of the ground spin state for 3 are analyzed and discussed in the framework of a spin polarization scheme.

The new bimetallic nickel(II) compound (PPh4)(4)[Ni-2(2)]. 6H(2)O (3), where H-8[2] stands for N,N',N",N'''-1,2,4,5-benzenetetrayltetrakis(oxamic acid), has been synthesized and its crystal structure determined by single-crystal X-ray diffraction. The structure of 3 consists of [Ni-2(eta(4):eta(4)-2)](4-) anions, tetraphenylphosphonium cations, and water molecules. Facile one-electron oxidation of the square-planar diamagnetic dinickel(II) complex [Ni-2(eta(4):eta(4)-2)](4-) generates the metallo-radical species [Ni-2(eta(4):eta(4)-2(.+))](3-) with characteristic intra-ligand pi-cation radical transitions in the visible region (475-550 nm) as well as a typical quasi-isotropic EPR signal at g approximate to 2.0.

A new manganese(IV) oxamato complex possessing a bis(µ-oxo)dimanganese core has been synthesized, magnetically and structurally characterized, and found to catalyze the aerobic oxidation of secondary alcohols to ketones with co-oxidation of pivalaldehyde to pivalic acid with good yields and high selectivities.

A new series of monomeric copper(II) complexes of the related substituted oxamate ligands N,N'-naphthalene-1,8-diylbis(oxamate) (L-2) and N,N'-trimethylenebis(oxamate) (L-3) have been synthesized. The molecular structures of [NBu4](2)[CuL2] and [PPh4](2)[CuL3]. 2H(2)O have been determined by single-crystal X-ray analysis. The structure of the previously reported complex [PPh4](2)[CuL1], where L-1 is the parent o-phenylenebis(oxamate), has been also determined. These are mononuclear four-co-ordinate copper(II) complexes with the metal center in a more or less distorted square-planar environment formed by the two amido nitrogen and two carboxylate oxygen atoms from the two oxamato groups of each tetradentate chelating ligand. The bond lengths at the metal atom are similar for all three complexes, the Cu-N bond distances (1.89-1.93 Angstrom) being shorter than the Cu-O ones (1.93-1.97 Angstrom). The bond angles around the metal are different from one complex to the other. They are closer to 90 degrees, corresponding to the ideal square-planar geometry, for the copper(II)-L-2 and -L-3 complexes as a result of the alternating 5-6-5-membered chelate ring system afforded by L-2 and L-3, respectively. The values of the Cu-III-Cu-II redox potential in acetonitrile for this family of complexes range from 0.41 to 0.27 V (vs. saturated calomel electrode, 25 degrees C and 0.1 mol dm(-3) NEt4ClO4 as supporting electrolyte), the redox process being only reversible for the copper(II)-L-3 species. The stabilization of the trivalent oxidation state of copper in this complex is attributed to the stronger basicity of the aliphatic amido nitrogens with respect to that of the aromatic amido ones. The trend in formal potential along this series is mainly controlled by the size of the chelate rings around the metal ion.

A family of related compounds of general formula (PPh4)2Mn2[Cu((L)]3nH2O, where PPh4+ is the tetraphenylphosphonium cation and L stands for ortho-phenylenebis(oxamate) (opba, 1), ortho-phenylene (N′-methyloxamidate) (oxamate) (Meopba, 2) and ortho-phenylenebis (N′-methyloxamidate) (Me2opba, 3), have been synthesized. The X-ray absorption near-edge structure (XANES) and extended X-ray Within absorption fine structure (EXAFS) spectra at both Mn and Cu K-edges for all three compounds, as well as their powder X-ray patterns, are consistent with a layered structure built up of parallel Mn11Cu11 two-dimensional honeycomb networks separated by PPh4+ cations. Within the antonic metallic layers, the manganese (II) ion in an octahedral environment is surrounded by three square-planar Cu(L) bisbidentate moieties with Mn...Cu separation of about 5.4Å. The magnetic properties of the three compounds have been investigated in the 1.8–300 K temperature range. Compounds 1–3 show characteristic ferrimagnetic behavior, with negative J values equal to − 31.8, − 32.6 and − 30.5 cm1, respectively. All three compounds show an abrupt ferromagnetic phase transition below a critical temperature Tc equal to 11.5, 13 and 8 K, for 1, 2 and 3, respectively. The magnetic ordering temperature values along this series of two-dimensional molecular-based magnets are analyzed and discussed in terms of the magnitude of the intramolecular interaction.

A new iron(III)–carbonato monomeric complex of ortho-phenylenebis(oxamato) (opba) 1 is synthesized, and spectroscopically and structurally characterized; it is a moderately efficient non-heme catalyst for the aerobic epoxidation of alkenes with co-oxidation of pivalaldehyde.

A family of related compounds of general formula (PPh4)2Mn2[Cu(L)]3·nH2O have been synthesized, where PPh4+ is the tetraphenylphosphonium cation and L stands for o-phenylenebis(N‘-benzyloxamidate) (PhMe2opbox) (1), o-phenylenebis[N‘-(3-phenylpropyl)oxamidate] (PhPr2opbox) (2), and o-phenylenebis[N‘-(4-phenylbutyl)oxamidate] (PhBu2opbox) (3). The analysis of the XANES and EXAFS spectra of 3 at both Mn and Cu K-edges reveals the occurrence of an oxamidato-bridged MnIICuII two- or three-dimensional structure with Mn···Cu separation of 5.4 A. Each manganese atom is surrounded by three Cu(L) bisbidentate entities which define an octahedral MnO6 environment, while each copper atom is in an essentially square-planar CuN4 surrounding. The magnetic properties of the three compounds have been investigated in the 1.8−300 K temperature range. Compounds 1−3 show characteristic ferrimagnetic behavior with a minimum in the χT versus T plot, and abrupt ferromagnetic phase transition below a critical temperature Tc equal ...

The dinuclear copper(II) complexes of formula [{Cu(Hdmg)(2)}(2)] 1, [{Cu(Hbdmg)}(2)][ClO4](2) 2, [{Cu(Hdeg)(2)}(2)] 3 and [{Cu(Hchd)(2)}(2)] 4 (H(2)dmg, H(2)bdmg, H(2)deg and H(2)chd = dimethylglyoxime, 3,10-dimethyl-4,9-diazadodeca-3,9-diene-2, 11-dione dioxime, diethylglyoxime and cyclohexane-l,2-dione dioxime) have been synthesized. The structures of 3 and 4 have been determined by single-crystal X-ray diffraction methods. Both consist of. centrosymmetric dinuclear bis(alkyl)glyoximatocopper(II) entities where the units are staggered so that the copper atom of one unit is directly opposite to the oxime-oxygen atom of the other, as previously found for 1 and 2. Each metal atom in 3 and 4 is five-co-ordinate with four imine nitrogen atoms comprising the basal plane and an oximate-oxygen atom in the apical position. The copper-imine nitrogen bond lengths (average 1.957 and 1.953 Angstrom. in 3 and 4, respectively) are shorter than that of the axial copper-oximate oxygen [2.263(3) (3) and 2.242(3) Angstrom (4)]. An oxime proton is lost from the ligand in the complex formation, the remaining oxime proton being involved in a hydrogen bond between the peripheral oxime oxygens of the same bis(alkyl)glyoximatocopper(II) unit. The intramolecular copper-copper separation is 3.898(1) (3)and 3.825(1) Angstrom (4). Variable-temperature magnetic susceptibility measurements showed the occurrence of intramolecular ferro-(1, 3 and 4) and antiferro-magnetic exchange interactions (2), the singlet-triplet energy gap J being +9.1 (1), -1.9 (2), +1.0 (3) and +3.1 cm(-1) (4). The analysis of the exchange pathway through the out-of-plane oximato bond in;this family has been substantiated by extended-Huckel calculations-and a quasi-linear correlation between the value of J and the angle at the Cu-O-N (alpha) has been found. The influence of the size of the imine-carbon alkyl substituents on both the nature and magnitude of J is discussed in the light of the available structural information.

N,N'-Bis(3-aminopropyl)oxamide (H(2)L(1)) which can adopt cis and trans conformations reacted with copper(rr) salts in its deprotonated form to yield the compounds [CuL(1)] 1, [Cu(3)L(2)(1) (NO3)(2)]. H2O 2, [Cu(2)L(1)(NO3)(2)] 3 and [Cu(2)L(1)(O(2)CMe)(2)]. 2H(2)O 4. The structures of 1, 3 and 4 have been determined by single-crystal X-ray diffraction methods. That of 1 consists of mononuclear [CuL(1)] units where the oxamidate is in a cis conformation co-ordinated to the copper atom through its four nitrogen atoms. The copper surroundings are close to square planar. The amidate-copper bond distance [1.955(6) Angstrom] is significantly Shorter than that involving the amine group [1.999(7) Angstrom]. The structures of 3 and 4 comprise centrosymmetric trans oxamidate-bridged copper(II) dinuclear units which are linked by asymmetric bis(monodentate) nitrate (3) and acetate (4) ligands to yield a Sheet-like polymer (3) and an alternating chain (4). The co-ordination geometry around each copper atom is distorted square pyramidal: the equatorial plane comprises the oxygen and nitrogen atoms of the amide, the nitrogen atom of the amine group and an oxygen atom from nitrate (3) or acetate (4) ligands. The apical position is filled by an oxygen atom from another nitrate (3) or acetate (4) group. The copper-copper separations across the oxamidate are 5.190(1) and 5.244(1) Angstrom for 3 and 4, respectively, and those across the nitrate and acetato groups are 5.116(1) and 3.350(1) Angstrom. Variable-temperature magnetic susceptibility measurements show a Curie law behaviour for 1 and the occurrence of a strong antiferromagnetic coupling through the oxamidate bridge in 2-4 (J = -325, -393 and -305 cm(-1), respectively). The versatility of L(1) as a ligand and its ability to mediate strong antiferromagnetic interactions is analysed and discussed.

The study of the magnetic properties of the compounds [M(III)Cu(II)(L)(2)(MeCO(2))(H2O)(2)], M = Mn and L = dimethylglyoximato (dmg) 1 or 1,2-cyclohexanedioneoximato (chd) 2 and M = Fe and L = dmg 3, shows that 1 is a metamagnetic compound, 2 is a bulk ferromagnet with T-c = 9 K and 3 orders antiferromagnetically at 7.5 K.

Copper(II) complexes of composition [Cu2(Hdmg)2(H2dmg) (H2O)2] [ClO4]2.H2O 1, [Cu2(dmg)(Hdmg)(H2dmg)]ClO4.1.5H2O 2 and [Cu3(dmg)2(H2dmg)2][ClO4]2.2H2O 3 (H2dmg = dimethylglyoxime) were obtained. The crystal structure of complex 1 was solved by single-crystal X-ray diffraction. It crystallizes in the monoclinic system, space group P2(1)/n, with a = 15.991(3), b = 11.682(1), c = 14.363(4) angstrom, beta = 90.82(5)degrees and Z = 4. The structure consists of cationic dinuclear [Cu2(Hdmg)2(H2dmg)(H2O)2]2+ units, unco-ordinated perchlorate anions and lattice water. The Cu(H2dmg)2+ fragment co-ordinates to the second copper(II) ion through the depronated oximate oxygens of Cu(HdMg)2 to afford a dinuclear structure doubly bridged by the oximate groups in a cis arrangement. The intramolecular Cu(1) ... Cu(2) separation is 3.526(4) angstrom. The configuration about the copper atoms is a distorted square pyramid: the basal plane for Cu (1 ) comprises two nitrogens of H2dmg and two oximate oxygens whereas that of Cu (2) is formed by four nitrogens of two Hdmg- groups; a water molecule occupies the apical position in both cases. Variable-temperature magnetic susceptibility measurements (50-300 K) on complexes 1-3 revealed the occurrence of a very strong intramolecular antiferromagnetic interaction through the oximate bridges. The formation of mononuclear, dinuclear and trinuclear copper(II) dimethylglyoxime complexes have been observed by spectrophotometry in ethanolic solutions of copper(II) perchlorate and [Cu(Hdmg)2]. A rational scheme accounting for the nature of the existing species has been proposed in the light of the coupled solution-solid state studies.