Beatriz Cervera

Oximato complexes. Part 1. Solution study, synthesis, structure, spectroscopic and magnetic properties of polynuclear copper(II) complexes containing dimethylglyoxime

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 P21/n, with a= 15.991(3), b= 11.682(1), c= 14.363(4)A, β= 90.82(5)° 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)A. 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.

A Square‐Planar Dinickel(II) Complex with a Noninnocent Dinucleating Oxamate Ligand: Evidence for a Ligand Radical Species

The new bimetallic nickel(II) compound (PPh4)4[Ni2(2)]·6H2O (3), where H8[2] stands for N,N′,N′′,N′′′-1,2,4,5-benzene-tetrayltetrakis(oxamic acid), has been synthesized and its crystal structure determined by single-crystal X-ray diffraction. The structure of 3 consists of [Ni2(η4:η4-2)]4– anions, tetraphenylphosphonium cations, and water molecules. Facile one-electron oxidation of the square-planar diamagnetic dinickel(II) complex [Ni2(η4:η4-2)]4– generates the metallo-radical species [Ni2(η4:η4-2·+)]3– with characteristic intra-ligand π-cation radical transitions in the visible region (475–550 nm) as well as a typical quasi-isotropic EPR signal at g ≈ 2.0.

Conformational change of the N,N′-bis(3-aminopropyl)oxamidate ligand in nuclearity tailoring copper(II) complexes

N,N′-Bis(3-aminopropyl)oxamide (H2L1) which can adopt cis and trans conformations reacted with copper(II) salts in its deprotonated form to yield the compounds [CuL1]1, [Cu3L21(NO3)2]·H2O 2, [Cu2L1(NO3)2]3 and [Cu2L1(O2CMe)2]·2H2O 4. The structures of 1, 3 and 4 have been determined by single-crystal X-ray diffraction methods. That of 1 consists of mononuclear [CuL1] 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)A] is significantly shorter than that involving the amine group [1.999(7)A]. The structures of 3 and 4 comprise centrosymmetric trans oxamidate-bridged copper(II) dinuclear units which are linked by asymmetric bis(monodenate) 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)A for 3 and 4, respectively, and those across the nitrato and acetato groups are 5.116(1) and 3.350(1)A. 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 L1 as a ligand and its ability to mediate strong antiferromagnetic interactions is analysed and discussed.

Interaction between heterobinuclear molecules and nature of the ground spin state in oximato-bridged [CuIIMII]2 bis-binuclear complexes (M=Cu, Ni, Mn): crystal structure of [Cu(pdmg)Ni(Me3[12]N3)(EtOH)](ClO4)2

Abstract Two new heterobimetallic complexes [Cu(pdmg)Ni(Me 3 [12]N 3 )(CH 3 CH 2 OH)](ClO 4 ) 2 ( 2 ) and [Cu(pdmg)Mn(bipy) 2 ](ClO 4 ) 2  · H 2 O ( 3 ) (H 2 pdmg=3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioxime; Me 3 [12]N 3 =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(Me 3 [12]N 3 )(CH 3 CH 2 OH)] 2+ cations and non-coordinated perchlorate anions. The [Cu(pdmg)(CH 3 CH 2 OH)] complex coordinates to the [Ni(Me 3 [12]N 3 )] 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) A. In the crystal, two [Cu II Ni II ] 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) A. 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 [Cu II Ni II ] 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)(H 2 O) 2 ](ClO 4 ) 2  · H 2 O ( 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 [Cu II Mn II ] 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.

Ferro- and ferri-magnetism in oximato-bridged MIIICuII chains (M = Mn and Fe). A molecular based ferromagnet with Tc= 9 K: [MnIIICuII-bis(1,2-cyclohexanedioneoximato)(acetato)(H2O)2]

The study of the magnetic properties of the compounds [MIIICuII(L)2(MeCO2)(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 Tc= 9 K and 3 orders antiferromagnetically at 7.5 K.

Tuning up the Tc in Mn(II)Cu(II) bimetallic planes and design of molecular-based magnets

Abstract 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 5.4A. 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.

An Na8 Cluster in the Structure of a Novel Oxamato-Bridged NaICuII Three-Dimensional Coordination Polymer

The new heterometallic sodium(I)-copper(II) compound Na4Cu2 (2) · 10.5 H2O (3), where H8[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 [Cu2(η4:η4-2)]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.

Tuning the nature of the exchange interaction in out-of-plane oximato-bridged dinuclear copper(II) complexes

The dinuclear copper(II) complexes of formula [{Cu(Hdmg) 2 } 2 ] 1, [{Cu(Hbdmg)} 2 ][ClO 4 ] 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-1,2-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 A in 3 and 4, respectively) are shorter than that of the axial copper–oximate oxygen [2.263(3) (3) and 2.242(3) A (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) A (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 (α) 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.