Oxalato Bridge Research Articles

Syntheses, crystal structures, and magnetic properties of one-dimensional oxalato-bridged Co(II), Ni(II), and Cu(II) complexes with n-aminopyridine (n = 2-4) as terminal ligand.

The reaction of M(ox) x 2H(2)O (M = Co(II), Ni(II)) or K(2)(Cu(ox)(2)) x 2H(2)O (ox = oxalate dianion) with n-ampy (n = 2, 3, 4; n-ampy = n-aminopyridine) and potassium oxalate monohydrate yields one-dimensional oxalato-bridged metal(II) complexes which have been characterized by FT-IR spectroscopy, variable-temperature magnetic measurements, and X-ray diffraction methods. The complexes M(mu-ox)(2-ampy)(2) (M = Co (1), Ni (2), Cu (3)) are isomorphous and crystallize in the monoclinic space group C2/c (No. 15), Z = 4, with unit cell parameters for 1 of a = 13.885(2) A, b = 11.010(2) A, c = 8.755(1) A, and beta = 94.21(2) degrees. The compounds M(mu-ox)(3-ampy)(2).1.5H(2)O (M = Co (4), Ni (5), Cu (6)) are also isomorphous and crystallize in the orthorhombic space group Pcnn (No. 52), Z = 8, with unit cell parameters for 6 of a = 12.387(1), b = 12.935(3), and c = 18.632(2) A. Compound Co(mu-ox)(4-ampy)(2) (7) crystallizes in the space group C2/c (No. 15), Z = 4, with unit cell parameters of a = 16.478(3) A, b = 5.484(1) A, c = 16.592(2) A, and beta = 117.76(1) degrees. Complexes M(mu-ox)(4-ampy)(2) (M = Ni (8), Cu (9)) crystallize in the orthorhombic space group Fddd (No. 70), Z = 8, with unit cell parameters for 8 of a = 5.342(1), b = 17.078(3), and c = 29.469(4) A. All compounds are comprised of one-dimensional chains in which M(n-ampy)(2)(2+) units are sequentially bridged by bis-bidentate oxalato ligands with M.M intrachain distances in the range of 5.34-5.66 A. In all cases, the metal atoms are six-coordinated to four oxygen atoms, belonging to two bridging oxalato ligands, and the endo-cyclic nitrogen atoms, from two n-ampy ligands, building distorted octahedral surroundings. The aromatic bases are bound to the metal atom in cis (1-6) or trans (7-9) positions. Magnetic susceptibility measurements in the temperature range of 2-300 K show the occurrence of antiferromagnetic intrachain interactions except for the compound 3 in which a weak ferromagnetic coupling is observed. Compound 7 shows spontaneous magnetization below 8 K, which corresponds to the presence of spin canted antiferromagnetism.

Syntheses, isolation, and structures of nickel(II) and copper(II) coordination polymers with a tetraaza macrocyclic ligand

The one-dimensional coordination polymers [Ni( L1)(oxalato)] n · nH 2O ( 1) and [Cu( L1)(terephthalato)] n ·2 nH 2O ( 2) have been synthesized and structurally characterized by a combination of analytical, spectroscopic, and crystallographic methods. The complex 1 exhibits a novel one-dimensional polymeric structure with nickel(II) centers and bridging oxalato ligands. Two important features are observed in 1 when regarding the structure of the oxalato bridge: first, it has an unusual bis-monodentate coordination mode to nickel(II) ions; and second, it is not planar, the distortion arising forms a twisting about the carbon–carbon bond of the oxalato ligand. In 2, the ligand conformation is planar, and the distorted octahedral coordination about the copper(II) ion is completed by two bis-monodentate terephthalato ligands. The copper(II) ions in the complex are bridged by the terephthalato anions to form infinite linear chains, and each chain is linked by interchain hydrogen bonding interactions mediated through water molecules. The presence of water molecules is crucial to lead supramolecular arrays in both complexes.

One-dimensional oxalato-bridged copper(II) complexes with 3-hydroxypyridine and 2-amino-4-methylpyridine

Two new one-dimensional oxalato-bridged copper(II) compounds of formula [Cu(ox)L 2] n ( 1) and {[Cu 2(ox) 2L′ 3]·L′} n ( 2) [ox=oxalate dianion, L=3-hydroxypyridine (pyOH) and L′=2-amino-4-methylpyridine (ampy)] have been synthesized and characterized by FT-IR spectroscopy, variable-temperature magnetic measurements and single-crystal X-ray diffraction. The crystal structure of 1 comprises chains of copper atoms in which cis-[Cu(pyOH) 2] 2+ units are sequentially bridged by asymmetric bis-bidentate oxalato ligands with an intrachain copper–copper separation of 5.548(1) Å. Each copper atom is six-coordinated: four oxygen atoms belonging to two bridging oxalato ligands and two nitrogen atoms from two 3-hydroxypyridine ligands build a distorted octahedral environment around the metal atom. As in 1, the structure of compound 2 is made up of chains of copper atoms bridged sequentially by bis-bidentate oxalato ligands. Two types of copper(II) ion, one being six-coordinated (Cu(1)) and the other five-coordinated (Cu(2)), alternate regularly within the chain. The environment around Cu(1) is elongated octahedral with two cis-coordinated pyridine–nitrogen and two oxygen atoms from two oxalate ligands building the equatorial plane, the apical positions being filled by two oxalate-oxygen atoms. The environment around Cu(2) is distorted square pyramidal with four oxalato-oxygen atoms in the basal plane, and the pyridine nitrogen atom from one aromatic base in the apical position. Magnetic susceptibility data in the temperature range 2.0–300 K reveal regular ferromagnetic ( J=+1.3 cm −1) and alternating antiferromagnetic ( J=−66.6 cm −1, αJ=−58.6 cm −1) chain behaviours for 1 and 2. The nature and magnitude of the magnetic coupling through the oxalato bridge in 1 and 2 are analysed and discussed in the light of the available structural data.

Syntheses, crystal structures, and magnetic properties of the oxalato-bridged mixed-valence complexes (FeII(bpm)3]2[FeIII2(ox)5].8H2O and FeII(bpm)3Na(H2O)2Fe(ox)(3).4H2O (bpm = 2,2'-bipyrimidine).

The preparation and crystal structures of two oxalato-bridged FeII-FeIII mixed-valence compounds, [FeII(bpm)3]2[FeIII2(ox)5].8H2O (1) and FeII(bpm)3Na(H2O)2FeIII(ox)(3).4H2O (2) (bpm = 2,2'-bipyrimidine; ox = oxalate dianion) are reported here. Complex 1 crystallizes in the triclinic system, space group P1, with a = 10.998(2) A, b = 13.073(3) A, c = 13.308(3) A, alpha = 101.95(2) degrees, beta = 109.20(2) degrees, gamma = 99.89(2) degrees, and Z = 1. Complex 2 crystallizes in the monoclinic system, space group P2(1)/c, with a = 12.609(2) A, b = 19.670(5) A, c = 15.843(3) A, beta = 99.46(1) degrees, and Z = 4. The structure of complex 1 consists of centrosymmetric oxalato-bridged dinuclear high-spin iron(III) [Fe2(ox)5]2- anions, tris-chelated low-spin iron(II) [Fe(bpm)3]2+ cations, and lattice water molecules. The iron atoms are hexacoordinated: six oxygen atoms (iron(III)) from two bidentate and one bisbidentate oxalato ligands and six nitrogen atoms (iron(II)) from three bidentate bpm groups. The Fe(III)-O(ox) and Fe(II)-N(bpm) bond distances vary in the ranges 1.967(3)-2.099(3) and 1.967(4)-1.995(3) A, respectively. The iron(III)-iron(III) separation across the bridging oxalato is 5.449(2) A, whereas the shortest intermolecular iron(III)-iron(II) distance is 6.841(2) A. The structure of complex 2 consists of neutral heterotrinuclear Fe(bpm)2Na(H2O)2Fe(ox)3 units and water molecules of crystallization. The tris-chelated low-spin iron(II) ([Fe(bpm)3]2+) and high-spin iron(III) ([Fe(ox)3]3-) entities act as bidentate ligands (through two bpm-nitrogen and two oxalato-oxygen atoms, respectively) toward the univalent sodium cation, yielding the trinuclear (bpm)2Fe(II)-bpm-Na(I)-ox-Fe(III)(ox)2 complex. Two cis-coordinated water molecules complete the distorted octahedral surrounding of the sodium atom. The ranges of the Fe(II)-N(bpm) and Fe(III)-O(ox) bond distances [1.968(6)-1.993(5) and 1.992(6)-2.024(6) A, respectively] compare well with those observed in 1. The Na-N(bpm) bond lengths (2.548(7) and 2.677(7) A) are longer than those of Na-O(ox) (2.514(7) and 2.380(7) A) and Na-O(water) (2.334(15) and 2.356(12) A). The intramolecular Fe(II)...Fe(III) separation is 6.763(2) A, whereas the shortest intermolecular Fe(II)...Fe(II) and Fe(III)...Fe(III) distances are 8.152(2) and 8.992(2) A, respectively. Magnetic susceptibility measurements in the temperature range 2.0-290 K for 1 reveal that the high-spin iron(III) ions are antiferromagnetically coupled (J = -6.6 cm-1, the Hamiltonian being defined as H = -JS1.S2). The magnitude of the antiferromagnetic coupling through the bridging oxalato in the magneto-structurally characterized family of formula [M2(ox)5](2m-10)+ (M = Fe(III) (1), Cr(III), and Ni(II)) is analyzed and discussed by means of a simple orbital model.

Spin topology and ferromagnetic coupling: synthesis and magnetic properties of [CuII3CrIII] tetranuclear complexes of [14]N4 macrocyclic oxamides

Three novel tetranuclear macrocyclic complexes, [(CuL1)3Cr](ClO4)3·3H2O (1), [(CuL2)3Cr](ClO4)3·3H2O (2) and [(CuL3)3Cr](ClO4)3·3H2O (3) [L1, L2 and L3 are the dianions of three [14]N4 and [15]N4 macrocyclic oxamides, namely 2,3-dioxo-5,6:13,14-dibenzo-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene,2,3-dioxo-5,6:13,14-dibenzo-9-methyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene and 2,3-dioxo-5,6:14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tetraazacyclotetradeca-7,12-diene, respectively], have been prepared and characterized. These complexes are the first examples of Cu3Cr species exhibiting spin topology with all the spins parallel in the ground state. Cryomagnetic studies on (1) (2–300 K) and (3) (77–300 K) revealed that the CuII and CrIII ions interact ferromagnetically through the oxamido bridge, with the exchange integral J = 6.7 cm−1 for (1) and J = 6.3 cm−1 for (3) based on Ĥ = −2J∑ŜiŜj. The ferromagnetic interaction has been rationalized in terms of strict orthogonality of the magnetic orbitals. The oxamido bridge is also more efficient than the oxalato bridge at propagating the ferromagnetic interaction.

Synthesis, crystal structure, and magnetic properties of a one-dimensional polymeric copper(II) complex containing an unusual 1,1'-bicoordinated oxalato bridge.

The crystal structure and the magnetic properties of the compound [Cu(μ-oxalato-O,O‘)(H2O)(4-aminopyridine)2]n, the first transition metal extended structure that exhibits a bridging oxalate anion in a 1,1‘-cis-bidentate coordination mode, are reported.

Studies of the synthesis and thermochemistry of coordinatively unsaturated chelate complexes (eta 5-C5Me5)IrL2 (L2 = TsNCH2CH2NTs, TsNCH2CO2, CO2CO2).

A comparative synthetic, structural, and thermochemical study on a series of chelate complexes containing the fragment (eta 5-C5Me5)Ir [(eta 5-C5Me5)Ir(TsNCH2CH2NTs) (1), (eta 5-C5Me5)Ir(TsNCH2CO2) (2), (eta 5-C5Me5)Ir(CO2CO2) (3)] was performed to clarify the roles of carboxylato and sulfonamido ligands. Whereas 1 and 2 are monomeric in solution and in the solid state, 3 appears to exist as an oligomer or polymer, (3)n, which can be broken up by addition of a ligand L such as a phosphine, CO, or 2-methoxypyridine to form (eta 5-C5Me5)Ir(L)(CO2CO2) (6). The synthesis of (3)n from [(eta 5-C5Me5)IrCl(mu-Cl)]2 required the use of silver oxalate in CH3CN, but if other solvents were used, the bridging oxalato complex (eta 5-C5Me5)IrCl(mu-eta 2-eta 2-C2O4)ClIr(eta 5-C5Me5) (7) was obtained and identified by X-ray diffraction. Enthalpies for reaction of THF-soluble monomers 1 and 2 with PMe3 were determined to be -28.7(0.5) and -28.5(0.4) kcal mol-1, respectively. The oligomerization behavior of 3 may be a result of reduced sigma- or pi-donation of carboxylato ligands compared to N-tosylamido ligands, because the values for nu CO in oxalato and bissulfonamido complexes 6-CO and (eta 5-C5Me5)Ir(CO)(TsNCH2CH2NTs) (4-CO) were 2064 and 2042 cm-1, respectively.

Direct determination of the single-ion anisotropy in a one-dimensional magnetic system by high-field EPR spectroscopy; synthesis, EPR, and X-ray structure of NixZn1-x(C2O4)(dmiz)2.

The synthesis, X-ray structure, and EPR measurements of the integer-spin linear-chain antiferromagnet [Ni(ox)(dmiz)2] (where ox = C2O4(2-) and dmiz = 1,2-dimethylimidazole) are presented. The sign and size of the single-ion zero field splitting (Zfs) of the divalent Ni have been determined by high field/high-frequency EPR spectroscopy. The spectra of powder samples of the derivatives [NixZn1-x(C2O4)(dmiz)2] for x = 0.09 and 0.07, at frequencies ranging from 110 to 440 GHz allowed the accurate determination of the zfs parameters D and E, with D = 1.875(4) cm(-1) and E = 0.38 cm(-1). The X-ray structure has been determined from measurements on a single crystal with x = 0.07. Structural parameters are as follows: a = 14.5252(7) A, b = 12.1916(8) A, c = 8.6850(8) A,beta = 97.460(6)degrees in space group C2/c. The zigzag chain contains octahedrally coordinated metal ions with two cis-oriented N-coordinated dmiz ligands and two cis-oriented, tetradentate bridging oxalato(2-) ligands, together resulting in a MN2O4 donor set. The structure was refined to a conventional R value of 0.073 for 1,051 observed reflections. Zn-O distances are 2.167(5) A and Zn-N = 2.098 A. Coordination angles vary for cis angles from 78.4 to 100.7 degrees, with trans angles varying from 163.9 degrees to 165.5 degrees.

Crystal structures and magnetic studies of six new nickel(II) amine μ-oxalato compounds

Six new nickel(II) binuclear oxalato-bridging compounds were obtained and crystal structures were solved at room temperature. Factors influencing the nitrite coordination modes are discussed. [ mer-Ni 2(3,3′-diamino- N-methyldipropylamine) 2(OH 2) 2(μ-OX)]Cl 2·3H 2O ( I), Ni 2C 16Cl 2H 48N 6O 9 is a μ-oxalato bridged dimer with a Medpt ligands in the mer conformation, a nitro(N) ligand trans to the N-methyl group and a water ligand trans to an oxalato oxygen. Green [ fac-Ni 2(3,3′-diamino- N-methyldipropylamine) 2(ONO) 2(μ-OX)] ( II), Ni 2C 16H 38N 8O 8 is also a μ-oxalato bridged dimer with a fac-Medpt, making this substance unique since it is the only fac-dpt compound ever made. The nitro(O) ligand is trans to the N-methyl group. Violet [ mer-Ni 2(3,3′-diamino- N-methyldipropylamine) 2(NO 2) 2(μ-OX)]·2H 2O ( III), Ni 2C 16H 42N 8O 10 is interesting as this compound came from the same reaction pot as II. The two are readily separated by hand since their colors differ drastically. It is also a μ-oxalato bridged dimer with mer-Medpt but the nitro ligand is (O) bound and trans to an oxalato oxygen. [ mer-Ni 2( N-(3-aminopropyl)-1,3-propanediamine) 2(OH 2) 2(μ-OX)]Cl 2 ( IV), Ni 2C 14Cl 2H 38N 6O 6 is also a μ-oxalato bridged dimer with an unmethylated dpt ligand in mer conformation. The sixth position of the coordination sphere is a water located trans to an oxalato oxygen. [ mer-Ni 2( N-(3-aminopropyl)-1,3-propanediamine) 2(OH 2) 2(μ-OX)]Cl(NO 2) ( V), Ni 2C 14ClH 38N 7O 8. The amine ligand of both nickels are mer, an oxalato bridge links the two metal centers and a water occupies a site trans to an oxalato oxygen. It is surprising to find a nitro ligand as a counter ion while a water occupies a coordination site. Normally, one would expect displacement of the aquo ligand by NO 2 − . [ mer-Ni 2( N-(2-aminoethyl)-1,3-propanediamine) 2(OH 2) 2(μ-OX)](ClO 4) 2 ( VI), Ni 2C 12Cl 2H 34N 6O 14. The mer-aep and the μ-oxalato ligands fill five positions of the coordination sphere of this dimer. The other positions are taken up by water molecules located trans to an oxalato oxygen. The structures of all six compounds were determined and the temperature dependence of their magnetic susceptibility were also established.

Synthesis, Crystal Structure, and Magnetic Properties of Tetraphenylarsonium Tetrachloro(oxalato)rhenate(IV) and Bis(2,2'-bipyridine)tetrachloro(&mgr;-oxalato)copper(II)rhenium(IV).

Two new rhenium(IV) compounds of formula (AsPh(4))(2)[ReCl(4)(ox)] (1) and [ReCl(4)(&mgr;-ox)Cu(bipy)(2)] (2) (AsPh(4) = tetraphenylarsonium cation, ox = oxalate anion, and bipy = 2,2'-bipyridine) have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. 1 and 2 crystallize in the monoclinic system, space groups P2(1)/c and P2(1)/n, respectively, with a = 22.250(5) Å, b = 11.245(3) Å, c = 19.089(4) Å, beta = 96.59(2) degrees, and Z = 4 for 1 and a = 9.421(2) Å, b = 16.909(4) Å, c = 16.179(4) Å, beta = 93.97(2) degrees, and Z = 4 for 2. The structure of 1 is made up of [ReCl(4)(ox)](2)(-) anions and AsPh(4)(+) cations held united by electrostatic forces. Rhenium(IV) is hexacoordinate, with two oxygens of a chelating ox and four chlorine atoms building a distorted octahedron around the metal atom. There is no contact between the [ReCl(4)(ox)](2)(-) anions, the shortest Re.Re and Cl.Cl distances being 10.345 and 7.209 Å, respectively. This anionic complex is coordinated to a [Cu(bipy)(2)](2+) cation in 2, through one oxalate-oxygen, giving a neutral heterometallic dinuclear unit. The Cu(II) ion shows a very distorted five-coordinated geometry, four bipy-nitrogens occuping the equatorial positions and the oxygen atom the apical one. The basal plane geometry is distorted toward the tetrahedron, the dihedral angle between the mean planes of the two bipy ligands is 37.6(2) degrees. These [ReCl(4)(&mgr;-ox)Cu(bipy)(2)] units are arranged in such a way that a chlorine atom of one of them points toward the copper atom of the neighboring one, forming helicoid chains. The intrachain Re.Cu distances through chloro and oxalato bridges are 4.658 and 4.798 Å, respectively. The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.8-300 K. 1 is a magnetically diluted Re(IV) complex, the great value of zero-field splitting of the ground level (D = 60 cm(-)(1)) accounting for the variation of chi(M)T with T in the low-temperature range. 2 behaves as a ferrimagnetic chain, with weak antiferromagnetic interactions between Re(IV) and Cu(II) through oxalato and single chloro bridges.

The Synthesis and Structure of A. New Oxomolybdenum Complex with Oxalate as Ligand

An oxomolybdenum complex with oxalate as ligand has been synthesized by the reaction of (NH4)2MoS4 and K2C2O4H2O in the presence of KOH. The crystal structure of the complex K2[MoO3(C2O4)]H, O (1) has been determined by X-ray diffraction. The crystals belong to the monocinic space group P21 /a, with a = 7.544 (1) Å, b = 12.767 (3) Å, c = 8.710 (4)Å, P. = 95.10 (2)°, Z. = 4, V. = 835.6 (5) Å3, F (OOO) = 632, R. = 0.025 and Rw = 0.042. The structure analysis reveals that the complex is a new infinite-chain compound, in which each molybdenum atom is coordinated to bridging oxo, terminal oxo and oxalato ligand, forming a distorted octahedron.

Synthesis, chemical characterization, X-ray crystal structure and magnetic properties of oxalato-bridged copper(II) binuclear complexes with 2,2′-bipyridine and diethylenetriamine as peripheral ligands

Two new μ-oxalato binuclear copper(II) complexes, [{Cu(NO 3)(H 2O)(bipy)} 2(ox)] ( 1) and [{Cu(dien)} 2(ox)](NO 3) 2 ( 2), with ox=oxalate, dien=diethylenetriamine and bipy=2,2′-bipyridine, have been synthesized and their crystal and molecular structures have been determined by single-crystal X-ray diffraction methods. The crystal structure of 1 consists of centrosymmetric neutral dimers where the copper atoms lie in a strongly elongated octahedral environment, surrounded by two nitrogen atoms of a bipy molecule and two oxygen atoms of the bridging oxalato group in the equatorial plane and oxygen atoms of water molecules and nitrate ions in the axial positions. Crystal structure of 2 is made up of non-coordinated nitrate anions and asymmetric binuclear cations in which copper atoms are in a distorted square–pyramidal coordination with three atoms of a diethylenetriamine ligand and an oxygen atom of the asymmetrically coordinated oxalato bridge building the basal plane and the other oxygen atom of the oxalato ligand filling the apical position. Both compounds have been also characterized by Fourier transform infrared (FT-IR) and electron spin resonance (ESR) spectroscopies, thermal analysis and variable temperature magnetic susceptibility measurements. The two compounds exhibit antiferromagnetic exchange with a singlet–triplet separation of −382 and −6.5 cm −1 for 1 and 2, respectively. Magnetic and ESR results are discussed with respect to the crystal structure of the compounds.

New Oxamido Bridged Molecular Based Magnets and High-Spin Molecules

The reaction of copper(II) bis-oxamido monomers with a manganese(II) salt leads to compounds 1, 2 and 3 of general formula (PPh4)2Mn2[CuL]3-nH2O where L= (PhMe2opbox)4−, (PhPr2opbox)4−, (PhBu2opbox)4− for 1, 2 and 3 respectively. Critical temperatures of 12.5, 11.5 and 13.5 K were measured for 1, 2 and 3 respectively. This range of temperature likely indicates that this family of compounds assumes a 2D structure. Two tetrameric complexes 10 and 11 were prepared from the Cr(III) tamox precursor. Magnetic investigations of 10 in the 2–300 K temperature range reveal a ferromagnetic interaction between the Cr(III) and Ni(II) magnetic centers with a spin coupling constant J estimated to be +10.8 cm−1 which is twice the value observed for the oxalato bridge. On the other hand, an antiferromagnetic exchange is observed for the CrMn3 complex 11. The magnetic behavior can be reproduced using the interaction parameter JCrMn= −3 cm-1, JMnMn= −0.5 cm-1, gCr=1.98 and gMn= 2.07.

Magnetism and photophysics in supramolecular transition-metal compounds

Based on a synthetic strategy, extended anionic, homo and bimetallic oxalato-bridged transition-metal compounds with two (2D) and three-dimensional (3D) connectivities can be synthesized and crystallized. Thereby, the choice of the templating counterions will determine the crystal chemistry. Since the oxalato bridge is a mediator for both antiferro and ferromagnetic interactions between similar and dissimilar metal ions, long-range magnetic ordering will occur. Examples of the determination of magnetic structures in 2D and 3D compounds by means of elastic neutron scattering methods will be discussed. In addition, due to the possibility of the variation of different metal ions in varying oxidation states, interesting photophysical processes can be observed within the extended three-dimensional host/guest systems.

Study of the interaction between [Cu(bipy)] 2+ and oxalate in dimethyl sulfoxide. Crystal structure of [Cu 2(bipy) 2(H 2O) 2ox]SO 4·[Cu(bipy)ox

A study of complex formation between [Cu(bipy)] 2+ and ox 2− (bipy and ox 2− being 2,2′-bipyridyl and the dianion of oxalic acid), has been carried out by potentiometry in dimethyl sulfoxide solution. The constants of the equilibria ▪ and ▪ are log β 110 = 11.165(1) and log β 210 = 13.185(5) at 25 °C and 0.1 mol dm −3 tetra-n- butylammonium perchlorate. The high values of these constants are consistent with the symmetrical bidentate and bis-bidentate modes of oxalate in [Cu(bipy)ox] and [Cu 2(bipy) 2ox] 2+ units, respectively, as shown by X-ray diffraction studies. Well-formed single crystals of [Cu 2(bipy) 2(H 2O) 2ox]SO 4· [Cu(bipy)ox] were grown from aqueous solutions and characterized by X-ray diffraction. The system is monoclinic, space group C2/ c, with a = 22.706(5), b = 10.485(3), c = 16.172(4) Å, β = 92.63(3)°, V = 3846(3) Å 3, Z = 4, D x = 1.670 g cm −3, μ(Mo Kα) = 18.38 cm −1, F(000) = 1956 and T = 298 K. A total of 3214 reflections was collected over the range 2⩽θ⩽25°; of these, 1099 (independent and with I⩾2.5σ( I) were used in the structural analysis. The final R and R w residuals were 0.067 and 0.070, respectively. The structure is made up of cationic centrosymmetric [Cu 2(bipy) 2ox] 2+ dinuclear units, neutral axiosymmetric [Cu(bipy)ox] mononuclear entities and SO 4 2− as a counterion. Each copper atom of the dinuclear unit shows a square-pyramidal environment with the two nitrogen atoms of 2,2′-bipyridyl and two oxygen atoms of oxalato bridge building the basal plane and an oxygen atom of a water molecule filling the apical position. The copper atom of the mononuclear unit is bound to two oxygen atoms of oxalate and two nitrogen atoms of 2,2′-bipyridyl forming a four-fold surrounding slightly deviating from planarity. In these complexes, copper coordination is 4 + 1 + 1 (dinuclear unit) or 4 + 2 (mononuclear unit) because of the weak binding of the sulfate group in a bis-monodentate fashion linking alternately dinuclear and mononuclear entities. This is a rare case where the two copper( II) complexes bound to the same ligands, that have been observed in solution, are found in the same compound in the solid state.

Crystal and molecular structure and magnetic properties of a new µ-oxalato binuclear copper(II) complex containing mepirizole

The crystal and molecular structure of the new µ-oxalato binuclear copper(II) complex [(mpym)(H2O)(NO3)Cu(C2O4)Cu(NO3)(H2O)(mpym)]·2H2O 1[mpym = mepirizole = 4-methoxy-2-(5-methoxy-3-methyl-1H-pyrazol-1-yl)-6-methylpyrimidine] has been determined by X-ray diffraction methods. It consists of discrete binuclear entities where the copper atoms lie in a strongly elongated octahedral environment, surrounded by two nitrogen atoms (one from each ring of a mepirizole molecule) and two oxygen atoms of the bridging oxalato group in the equatorial plane and oxygen atoms of water molecules and nitrate ions in the axial positions. The binuclear entities are not centrosymmetric and the difference in the ligand environments of the copper(II) ions induces and energy separation between the two magnetic orbitals large enough to weaken the antiferromagnetic interaction (J=–142 cm–1) by approximately 60 cm–1 compared to that of symmetrical µ-oxalato binuclear copper(II) compounds. ESR, vibrational and electronic spectra are consistent with the above results.

Formation and degradation of an oxalato and peroxo bridged dicobalt bisdien dioxygen complex: a binuclear complex as host for the activation of two co-ordinated guests

The dioxygen complex of the dicobalt bisdien complex co-ordinates with and oxidizes a bridging oxalato group, thus providing the first example of a redox reaction between two co-ordinated ligands within the cavity of a binuclear macrocyclic complex.

Structure of a binuclear nickel(II) complex of a pyridine-containing tetraaza macrocycle, including a tetradentate oxalato bridge, [(L)Ni(μ-ox)Ni(L)](ClO4)2

Structure of a binuclear nickel(II) complex of a pyridine-containing tetraaza macrocycle, including a tetradentate oxalato bridge, [(L)Ni(μ-ox)Ni(L)](ClO4)2

ChemInform Abstract: INTERACTIONS IN COPPER(II)‐COPPER(II), VANADYL(II)‐VANADYL(II), AND COPPER(II)‐VANADYL(II) PAIRS THROUGH OXALATO BRIDGING LIGAND

Chemischer InformationsdienstVolume 15, Issue 17 Physical Organic Chemistry ChemInform Abstract: INTERACTIONS IN COPPER(II)-COPPER(II), VANADYL(II)-VANADYL(II), AND COPPER(II)-VANADYL(II) PAIRS THROUGH OXALATO BRIDGING LIGAND M. JULVE, Search for more papers by this authorM. VERDAGUER, Search for more papers by this authorM.-F. CHARLOT, Search for more papers by this authorO. KAHN, Search for more papers by this authorR. CLAUDE, Search for more papers by this author M. JULVE, Search for more papers by this authorM. VERDAGUER, Search for more papers by this authorM.-F. CHARLOT, Search for more papers by this authorO. KAHN, Search for more papers by this authorR. CLAUDE, Search for more papers by this author First published: April 24, 1984 https://doi.org/10.1002/chin.198417055AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume15, Issue17April 24, 1984 RelatedInformation

Interactions in Cu(II)Cu(II), VO(II)VO(II) and Cu(II)VO(II) pairs through oxalato bridging ligand

The goal of this paper was to compare the interaction in Cu(II)Cu(II), VO(II)VO(II) and Cu(II)VO(II) pairs through the same oxalato bridging ligand. For this, two new bimetallic complexes were synthesized, namely acacVO(C 2O 4)VOacac·4H 2O noted [VOVO] and tmenCu(C 2O 4)VO(C 2O 4)·3H 2O noted [CuVO], with acac = acetylacetonato and tmen = N,N,N′,N′-tetramethylethylenediamine. The [CuCu] compound of formula [tmen(H 2O)Cu(C 2O 4)Cu(H 2O)tmen] (ClO 4) 2·1.25H 2O has already been described and its crystal structure solved by X-ray diffraction. The singlet-triplet energy gaps arising from the intramolecular interaction, determined from the magnetic data, are −385.4 cm −1 in [CuCu], −5.75 cm −1 in [VOVO] and ∣J∣ < 1 cm −1 in [CuVO]. The EPR spectrum of this last compound, however, shows a transition in a triplet state with a singlet-triplet energy gap larger, in absolute value, than the incident quantum (∼0.3 cm −1 in X-band). To obtain this result, the spectrum was compared to those of the monomeric species tmenCu(C 2O 4)·4H 2O and (NH 4) 2VO(C 2O 4) 2·2H 2O. The magnitude of the singlet-triplet gaps J was rationalized within the framework of an orbital model developed in our group. [CuVO] is a new heterobimetallic compound in which the interaction is expected to be purely ferromagnetic owing to the strict orthogonality of the magnetic orbitals. Finally, an explanation of the absence of zero field splitting in the triplet state of [CuCu] was proposed. It was shown that the anisotropic exchange interaction in [CuCu] might be considered as being proportional to the isotropic exchange interaction in [CuVO].