Oxalato Groups Research Articles

Synthesis, crystal structure, and spectroscopic properties of bis(rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)(μ-1,2,3,4-oxalato)dichloridozincate(II)(μ-1,2,3-oxalato)dichromium(III) tetrachloridozincate monohydrate

A novel oxalato-bridged trinuclear heterometallic complex, cis-[Cr(cyc b)(μ-1,2,3,4-ox)ZnCl2(μ-1,2,3-ox)Cr(cyc b)]ZnCl4·H2O (1) (cyc b = rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane; C16H36N4, ox = oxalate; C2O42−), was prepared and its structure was determined by single-crystal X-ray diffraction analysis at 100 K. Complex 1 crystallizes in the orthorhombic system space group Pca21, with a = 31.702(6), b = 9.087(2), c = 17.677(4) Å, and Z = 4. The two [Cr(cyc b)]3+ units are bridged by the central Zn(II) atom through the oxalato groups, which present bis-bidentate (μ-1,2,3,4-ox) and bidentate-monodentate (μ-1,2,3-ox) modes. Each Cr(III) ion is coordinated by four N atoms from the cyc b ligand and two O atoms of the oxalato ligand in cis-V conformation. The central Zn(II) ion is coordinated in a distorted trigonal-bipyramidal geometry formed by two Cl atoms and two O atoms from μ-1,2,3,4-ox and one O atom from μ-1,2,3-ox. However, the ZnCl42− anion and the uncoordinated water molecule remain outside the coordination sphere. Infrared, UV–visible, and electron paramagnetic resonance spectroscopic analyses confirmed the structural data.

Synthesis, crystal structure and characterization of chiral, three-dimensional anhydrous potassium tris(oxalato)ferrate(III)

The synthesis, crystal structure and physical properties of chiral, three-dimensional anhydrous potassium tris(oxalato)ferrate(III) [K3Fe(C2O4)3] are described. X-ray analysis reveals that the compound crystallized in the chiral space group P4132 of cubic system with a¼ b¼c ¼ 13.5970(2), Z¼4. The structure of the complex consists of infinite anionic [Fe(C2O4)3] 3� units with distorted octahedral environment of iron surrounded by six oxygen atoms of three oxalato groups. The anionic units are interlinked through K þ ions of three different coordination environments of distorted octahedral, bicapped trigonal prismatic and trigonal prismatic yielding a three-dimensional motif. The two broad absorption bands at 644 and 924 nm from UV–vis–NIR transmittance spectra were ascribed to a ligandto-metal charge transfer. The room temperature crystalline EPR spectra indicate the high-spin (S ¼5/2) of Fe(III) ion. The vibrating sample magnetometer measurement shows the paramagnetic nature at room temperature. Thermal studies of the compound confirm the absence of water molecule.

Magnetic coupling and spin topology in linear oxalato-bridged tetranuclear chromium(III)–copper(II) complexes with aromatic diimine ligands

A novel heterotetranuclear chromium(III)–copper(II) complex of formula {[CrIII(bpy)(ox)2]2CuII2(bpy)2(ox)}·6H2O (1) has been synthesized by the ligand exchange reaction between Ph4P[CrIII(bpy)(ox)2]·H2O and [CuII(bpy)2(NO3)]NO3·MeOH in methanol (bpy=2,2′-bipyridine; ox2−=oxalate dianion). The X-ray crystal structure of 1 consists of neutral oxalato-bridged CrIII2Cu2II zigzag entities which are formed by the monodentate coordination of two [CrIII(bpy)(ox)2]− mononuclear anionic units through one of its two oxalato groups toward a [CuII2(bpy)2(ox)]2+ dinuclear cationic moiety featuring relatively long axial bonds at the square pyramidal CuII ions. Variable temperature (2.0–300K) magnetic susceptibility and variable-field (0–5.0T) magnetization measurements for 1 have been interpreted on the basis of the linear tetranuclear topology of the CrIII2CuII2 entities [H=–J(S1·S2+S3·S4)–J′S2·S3 with S1=S4=SCr=3/2 and S2=S3=SCu=1/2]. A weak antiferromagnetic coupling occurs between the outer CrIII and inner CuII ions through the peripheral bidentate/monodentate(outer) oxalates (J=–8.7cm−1), while a strong antiferromagnetic coupling is operative between the inner CuII ions across the central bis-bidentate oxalate (J′=–472.2cm−1), leading thus to a S=(SCr–SCu)–(SCr–SCu)=0 ground spin state for the CrIII2CuII2 entity of 1. A simple orbital analysis of the electron exchange interaction in the oxalato-bridged CuII2 and CrIIICuII fragments identify the σ-type pathways involving the dx2-y2(Cu)/dx2-y2(Cu) and dxy(Cr)/dx2-y2(Cu) pairs of magnetic orbitals as the two main contributions responsible for the different strength of the intramolecular magnetic coupling parameters for 1. A magneto-structural correlation between the nature and magnitude of the magnetic coupling and the bending angle at the axial carbonyl-oxygen to copper bond has been established for 1 and related oxalato-bridged chromium(III)–copper(II) dinuclear complexes.

Theoretical Insights into the Ferromagnetic Coupling in Oxalato-Bridged Chromium(III)-Cobalt(II) and Chromium(III)-Manganese(II) Dinuclear Complexes with Aromatic Diimine Ligands

Two novel heterobimetallic complexes of formula [Cr(bpy)(ox)(2)Co(Me(2)phen)(H(2)O)(2)][Cr(bpy)(ox)(2)]·4H(2)O (1) and [Cr(phen)(ox)(2)Mn(phen)(H(2)O)(2)][Cr(phen)(ox)(2)]·H(2)O (2) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and Me(2)phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the "complex-as-ligand/complex-as-metal" strategy by using Ph(4)P[CrL(ox)(2)]·H(2)O (L = bpy and phen) and [ML'(H(2)O)(4)](NO(3))(2) (M = Co and Mn; L' = phen and Me(2)phen) as precursors. The X-ray crystal structures of 1 and 2 consist of bis(oxalato)chromate(III) mononuclear anions, [Cr(III)L(ox)(2)](-), and oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear cations, [Cr(III)L(ox)(μ-ox)M(II)L'(H(2)O)(2)](+)[M = Co, L = bpy, and L' = Me(2)phen (1); M = Mn and L = L' = phen (2)]. These oxalato-bridged Cr(III)M(II) dinuclear cationic entities of 1 and 2 result from the coordination of a [Cr(III)L(ox)(2)](-) unit through one of its two oxalato groups toward a [M(II)L'(H(2)O)(2)](2+) moiety with either a trans- (M = Co) or a cis-diaqua (M = Mn) configuration. The two distinct Cr(III) ions in 1 and 2 adopt a similar trigonally compressed octahedral geometry, while the high-spin M(II) ions exhibit an axially (M = Co) or trigonally compressed (M = Mn) octahedral geometry in 1 and 2, respectively. Variable temperature (2.0-300 K) magnetic susceptibility and variable-field (0-5.0 T) magnetization measurements for 1 and 2 reveal the presence of weak intramolecular ferromagnetic interactions between the Cr(III) (S(Cr) = 3/2) ion and the high-spin Co(II) (S(Co) = 3/2) or Mn(II) (S(Mn) = 5/2) ions across the oxalato bridge within the Cr(III)M(II) dinuclear cationic entities (M = Co and Mn) [J = +2.2 (1) and +1.2 cm(-1) (2); H = -JS(Cr)·S(M)]. Density functional electronic structure calculations for 1 and 2 support the occurrence of S = 3 Cr(III)Co(II) and S = 4 Cr(III)Mn(II) ground spin states, respectively. A simple molecular orbital analysis of the electron exchange mechanism suggests a subtle competition between individual ferro- and antiferromagnetic contributions through the σ- and/or π-type pathways of the oxalato bridge, mainly involving the d(yz)(Cr)/d(xy)(M), d(xz)(Cr)/d(xy)(M), d(x(2)-y(2))(Cr)/d(xy)(M), d(yz)(Cr)/d(xz)(M), and d(xz)(Cr)/d(yz)(M) pairs of orthogonal magnetic orbitals and the d(x(2)-y(2))(Cr)/d(x(2)-y(2))(M), d(xz)(Cr)/d(xz)(M), and d(yz)(Cr)/d(yz)(M) pairs of nonorthogonal magnetic orbitals, which would be ultimately responsible for the relative magnitude of the overall ferromagnetic coupling in 1 and 2.

Low-Dimensional Copper(II) Complexes with the Trinucleating Ligand 2,4,6-Tris(di-2-pyridylamine)-1,3,5-triazine: Synthesis, Crystal Structures, and Magnetic Properties†

The preparation and structural characterization of three new copper(II) complexes of formula [Cu(3)(dipyatriz)(2)(H(2)O)(3)](ClO(4))(6) x 2 H(2)O (1), {[Cu(4)(dipyatriz)(2)(H(2)O)(2)(NO(3))(2)(ox)(2)](NO(3))(2) x 2 H(2)O}(n) (2), and [Cu(6)(dipyatriz)(2)(H(2)O)(9)(NO(3))(3)(ox)(3)](NO(3))(3) x 4 H(2)O (3) [dipyatriz = 2,4,6-tris(di-2-pyridylamine)-1,3,5-triazine and ox = oxalate] are reported. The structure of 1 consists of trinuclear units [Cu(3)(dipyatriz)(2)(H(2)O)(3)](6+) and uncoordinated perchlorate anions. The two dipyatriz molecules in 1 act as tris-bidentate ligands with the triazine cores being in a quasi eclipsed conformation. Each copper atom in 1 exhibits a distorted square pyramidal geometry CuN(4)O with four pyridyl-nitrogen atoms from two dipyatriz ligands building the basal plane and a water molecule occupying the axial position. The values of the intratrimer copper-copper separation are 8.0755(6) and 8.3598(8) A. Compound 2 exhibits a layered structure of copper(II) ions which are connected through bis-bidentate dipyatriz ligands and bidentate/outer monodentate oxalato groups. The copper atoms in 2 exhibit six- [Cu(1)N(4)O(2)] and five-coordination [Cu(2)N(2)O(3)]. A water molecule and three pyridyl-nitrogen atoms [Cu(1)] and two pyridyl-nitrogen plus two oxalate-oxygen atoms [Cu(2)] define the equatorial plane whereas either an oxalate-oxygen and a pyridyl-nitrogen [Cu(1)] or a nitrate-oxygen [Cu(2)] fill the axial positions. The copper-copper separation through the bridging oxalato is 5.6091(6) A whereas those across dipyatriz vary in the range 7.801(1)-9.079(1) A. The structure of compound 3 contains discrete cage-like hexacopper(II) units [Cu(6)(dipyatriz)(2)(H(2)O)(9)(NO(3))(3)(ox)(3)](3+) where two trinuclear [Cu(3)(dipyatriz)](6+) fragments are connected by three bis-bidentate oxalate ligands, the charge being balanced by three non-coordinated nitrate anions. The values of the intracage copper-copper distance are 5.112(3)-5.149(2) A (across oxalato) and 7.476(2)-8.098(2) A (through dipyatriz). Magnetic susceptibility measurements of polycrystalline samples of 1-3 in the temperature range 1.9-295 K show the occurrence of a weak antiferromagnetic interaction across dipyatriz in 1 [J = -0.08(1) cm(-1), the Hamiltonian being defined as (wedge)H = -J ((wedge)S(1).(wedge)S(2) + (wedge)S(1) x (wedge)S(3) + (wedge)S(2) x (wedge)S(3))] and weak ferro- (2) and strong antiferromagnetic (3) interactions through the oxalato bridge in 2 [J = +0.45(2) cm(-1)] and 3 [J = -390(1) cm(-1)]. The use of the dipyatriz-containing copper(II) species as a building block to design homo- and heterometallic magnetic compounds is analyzed and discussed.

EXAFS characterization of oxaliplatin anticancer drug and its degradation in chloride media

Oxaliplatin is a second-generation platinum-based anticancer drug. Its degradation is studied in solution, in the presence of chloride ions (in neutral or acidic media) in excess. In both cases the degradation product precipitates immediately. The EXAFS spectra of these products show that they are identical. EXAFS modeling and refinement of the first coordination sphere shows that two light atoms are replaced by two chloride ions. The complete refinement of the local structure is possible by studying the multiple-scattering signal. The results show that the main multiple-scattering contribution is due to the binding oxalato group and that the degradation product is [Cl(2)-(diaminocyclohexane)-Pt(II)].

Two new oxalato-bridged dinuclear copper(II) complexes with di-2-pyridylamine: crystal structures, spectroscopic and magnetic properties

Two dinuclear Cu(II) complexes of formula [Cu 2(dpyam) 2(μ-C 2O 4)(Cl) 2] ( 1) and [Cu 2(dpyam) 2(μ-C 2O 4)(CF 3SO 3) 2] n ( 2) (dpyam = di-2-pyridylamine) have been synthesized and their spectroscopic and magnetic properties characterized. The structure of 1 is made up of the centrosymmetric dinuclear [{Cu(dpyam)(Cl)} 2(μ-C 2O 4)] units, while 2 contains chains of the dimeric [Cu 2(dpyam) 2(μ-C 2O 4)(CF 3SO 3) 2] units linked by the triflate anions. The two copper atoms in both compounds are linked through a bis-didentate oxalato group leading to a metal–metal separation of 5.526(1) and 5.228(3) Å. The stereochemistry of the Cu(II) chromophore in 1 is approximately square pyramidal, while compound 2 displays an elongated octahedral Cu(II) environment. The IR, ligand field and EPR measurements are in agreement with the structures found. The magnetic susceptibility measurements, measured from 5 to 350 K, revealed a very strong antiferromagnetic interaction between the Cu(II) atoms with a singlet–triplet energy gap ( J) of −274 and −342 cm −1, for compounds 1 and 2, respectively, in agreement with the coplanarity of the magnetic orbitals.

Bis and tris(oxalato)ferrate(iii) complexes as precursors of polynuclear compounds

The preparation and crystal structure of two oxalato-bridged NaI–FeIII compounds, [Na3Fe(ox)3(H2O)4]·H2O (1) and [FeII(phen)3][NaFe(ox)3(H2O)3]·4H2O (5), two mononuclear FeIII complexes AsPh4[Fe(bipy)(ox)2]·H2O (3) and AsPh4[Fe(phen)(ox)2]·H2O (4) and an oxalato-bridged FeIII compound [AsPh4]4[Fe2(ox)5]·5H2O (2) (ox = oxalate dianion, bipy = 2,2′-bipyridine, phen = 1,10-phenantroline and AsPh4+ = tetraphenylarsonium cation) are reported here. The structure of 1 consists of infinite anionic [NaFe(ox)3]2− layers linked trough centrosymmetric [Na4(H2O)8]4+ tetranuclear units yielding a three-dimensional motif. Crystallization water molecules ensure the cohesion of the crystal lattice in 1. The iron environment is distorted octahedral being surrounded by six oxygen atoms of three oxalate groups, with an average iron to oxalate-oxygen bond distance of 2.012(3) A. There are four crystallographically independent sodium atoms, all of which have a highly distorted octahedral environment. Six oxalate-oxygen atoms are bound to Na(1) and Na(2), whereas the other two sodium atoms are surrounded by four water oxygen and two oxalate oxygen atoms [Na(3)] and three water oxygen and three oxalate oxygen atoms [Na(4)]. The structure of compound 2 consists of centrosymmetric dinuclear [Fe2(ox)5]4− anions, AsPh4+ cations and crystallization water molecules. The anionic unit contains two Fe(III) atoms, four bidentate and one bridging oxalato ligands. Each iron atom has a distorted octahedral environment. The structures of 3 and 4 consist of discrete [Fe(AA)(ox)2]− [AA = bipy (3) and phen (4)] anions, tetraphenylarsonium cations and uncoordinated water molecules which are linked by hydrogen bonds. Each iron atom is six-coordinated with two nitrogen atoms from the bidentate AA ligand and four oxalate-oxygen atoms building a distorted octahedral environment. The structure of compound 5 consists of anionic [Fe(ox)3Na(H2O)3]2− chains, tris-chelated low-spin iron(II) [Fe(phen)3]2+ units and lattice water molecules linked to the chains through hydrogen bonds in which the water molecules and oxygen atoms of the oxalate groups are involved. The chains contain Fe3+ and Na+ cations alternatively bridged by oxalate groups, the tris-chelated [Fe(ox)3]3− unit acting as a bidentate ligand through one oxalato group toward a central sodium atom. Magnetic susceptibilty measurements in the temperature range 2.0–290 K for 2 that reveal the occurrence of antiferromagnetic coupling (J = −6.5 cm−1, the Hamiltonian being defined as H = −JS1S2) between the high-spin iron(III) ions across the oxalato bridge.

Dinuclear copper(II) complexes with ferromagnetic and antiferromagnetic interactions mediated by a bridging oxalato group: structures and magnetic properties of [Cu2L4(μ-C2O4)](PF6)2(H2O)2 and [Cu2L2(μ-C2O4)(NO3)2((CH3)2NCOH)2] (L = di-2-pyridylamine)

Two dinuclear CuII complexes of formula [Cu2(dpyam)4(μ-C2O4)](PF6)2(H2O)2(1) and [Cu2(dpyam)2(μ-C2O4)(NO3)2(DMF)2] (2) (dpyam=di-2-pyridylamine) have been synthesized and their spectroscopic and magnetic properties characterized. Complex (1) crystallizes in the non-centrosymmetric monoclinic space group Pc, while (2) crystallizes in the non-centrosymmetric triclinic space group P1. Compound (1) involves the compressed octahedral CuII environment, whereas (2) exhibits an elongated octahedral CuII geometry. Both complexes contain six-coordinate metal centers bridged by planar bis-didentate oxalate group. The geometry, spectroscopic properties and the effective magnetic moment of (1) are very close to those of the recently published [Cu2(dpyam)4 (μ-C2O4)](ClO4)2(H2O)3 and [Cu2(dpyam)4(μ-C2O4)](BF4)2(H2O)3. Thus (1) is expected to exhibit a very weak ferromagnetic interaction between the CuII centers which is confirmed by EPR spectrum. Those of (2) are comparable to those of the recently published [Cu2(dpyam)2(μ-C2O4)(NO3)2(DMSO)2]. Therefore a strong antiferomagnetic interaction is expected. The effective magnetic moment at room temperature of (1) was measured to be 2.55 BM/dimer, which agrees with the spin only value of CuII, 2.45BM calculated for two uncoupled spin=1/2 centers. In (2) the room temperature effective magnetic moment of 2.16 BM/dimer indicates the partial spin paring by antiferromagnetic coupling. This is confirmed by the e.p.r. spectrum and is explained as a result of the magnetic interaction between the coplanar \({\rm d}_{x^2-y^2}\) orbitals on the two copper atoms.

Synthesis, crystal structures and magnetic properties of new oxalato- and phenolato-bridged binuclear copper(II) complexes with Schiff-base ligands

Two binuclear complexes of copper(II), [(Hfsaaep)Cu(μ-C 2O 4)Cu(Hfsaaep)] ( 1) and [Cu 2(Hfsadmpn) 2(H 2O) 2](ClO 4) 2 ( 2), have been synthesized by using Schiff-base ligands derived from 3-formyl-salicylic acid: 3-[ N-2-(pyridylethyl)formimidoyl]salicylic acid (H 2fsaaep) and 3- N-[ N′, N′-dimethylaminopropyl)formimidoyl]salicylic acid (H 2fsadmpn). The crystal structures of compounds 1 and 2 have been solved. That of compound 1 consists of neutral binuclear entities with copper atoms bridged by one oxalato group, which connect axial–equatorial positions of the two coordination polyhedra. The copper atoms are related by an inversion center and exhibit a distorted square-pyramidal stereochemistry. The Cu⋯Cu distance within the binuclear unit is 5.482(1) Å. The structure of 2 consists of cationic centrosymmetric binuclear entities and perchlorate anions. The tertiary amino groups from the ligands are protonated. The copper(II) ions are bridged by phenolic oxygen atoms, assuming a square-pyramidal geometry bridge the copper(II) ions. The apical positions are occupied by the aqua ligands (CuO=2.335(4) Å). The distance between the copper atoms is 3.008(2) Å. Cryomagnetic investigations of the two compounds reveal antiferromagnetic interactions between the copper ions in both compounds ( 1: J=−9 cm −1; 2: J=−646 cm −1).

Novel chiral three-dimensional iron(III) compound exhibiting magnetic ordering at T(c) = 40 K.

The preparation and crystal structure determination of the iron(III) compound of formula [(NH(4))(2)[Fe(2)O(ox)(2)Cl(2)].2H(2)O](n) (1) (ox = oxalate dianion) are reported here. Complex 1 crystallizes in the orthorhombic system, space group Fdd2, with a = 14.956(7) A, b = 23.671(9) A, c = 9.026(4) A, and Z = 8. The structure of complex 1 consists of the chiral anionic three-dimensional network [Fe(2)O(ox)(2)Cl(2)](2-) where the iron(III) ions are connected by single oxo and bisbidentate oxalato groups. The metal-metal separations through these bridging ligands are 3.384(2) and 5.496(2) A, respectively. Ammonium cations and crystallization water molecules are located in the helical pseudohexagonal tunnels defined by iron atoms. The longest iron-iron distance in the pseudohexagonal tunnel is 15.778(2) A whereas the shortest one is 8.734(2) A. The iron atoms are hexacoordinated: a terminal chloro ligand and five oxygen atoms, that of the oxo group and four from two cis coordinated oxalate ligands, build a distorted octahedral environment around the metal atom. The Fe-O(oxo) bond distance [1.825(2) A] is significantly shorter than the Fe(III)-O(ox) [average value 2.103(4) A] and Fe(III)-Cl bond distances [2.314(2) A]. Magnetic susceptibility measurements of 1 in the temperature range 2.0-300 K reveal the occurrence of a susceptibility maximum at 195 K and a transition toward a magnetically ordered state in the lower temperature region with T(c) = 40 K. The strong antiferromagnetic coupling through the oxo bridge (J = -46.4 cm(-1), the Hamiltonian being H = -JS(A).S(B)) accounts for the susceptibility maximum whereas a weak spin canting of approximately 0.3 degrees due to the antisymmetric magnetic exchange within the chiral three-dimensional network is responsible for the magnetic ordering. The values of coercive field (H(c)) and remnant magnetization (M(r)) obtained from the hysteresis loop of 1 at 5 K are 4000 G and 0.016 micro(B).

Synthesis, crystal structure and magnetic properties of [Cu(bipy) 2(CH 3COO)][Cu(bipy) 2(Cr(C 2O 4) 3)]·∼10.5H 2O, the first compound containing the [Cr(C 2O 4) 3] 3− building block acting as a monodentate ligand

The reaction between copper(II) acetate with 2,2′-bipyridine and K 3[Cr(C 2O 4) 3] leads to the novel salt [Cu(bipy) 2(CH 3COO)][Cu(bipy) 2(Cr(C 2O 4) 3)]·∼10.5H 2O, 1 (bipy=2,2′-bipyridine). The crystal structure of 1 consists of mononuclear cationic species [Cu(bipy) 2(CH 3COO)] + and heterobinuclear anionic units, [Cu(bipy) 2(Cr(C 2O 4) 3)] −. The tris-oxalato-chromium entity behaves as a monodentate ligand toward the copper(II) ion within the complex anion. The distance between Cr(III) and Cu(II) across the bridging oxalato group is 5.056(2) Å. The copper(II) ions exhibit a distorted trigonal bipyramidal surrounding in both cationic and anionic species. The π–π stacking interaction between bipy ligands of the neighboring [Cu(bipy) 2(CH 3COO)] + mononuclear entities leads to chains of copper atoms running along the b axis. Magnetic susceptibility measurements of 1 in the temperature range of 1.9–290 K reveal a quasi-Curie law behavior, the magnetic coupling between Cr(III) and Cu(II) through the bridging oxalato group with the bidentate/monodentate coordination mode being negligible.

Cr(dpa)(ox)2]–: a new bis-oxalato building block for the design of heteropolymetallic systems. Crystal structures and magnetic properties of PPh4[Cr(dpa)(ox)2], AsPh4[Cr(dpa)(ox)2], Hdpa[Cr(dpa)(ox)2]·4H2O, Rad[Cr(dpa)(ox)2]·H2O and Sr[Cr(dpa)(ox)2]2·8H2O (dpa = 2,2′-dipyridylamine)

The new complexes of formulae PPh4[Cr(dpa)(ox)2] (1), AsPh4[Cr(dpa)(ox)2] (2), Hdpa[Cr(dpa)(ox)2]·4H2O (3), Rad[Cr(dpa)(ox)2]·H2O (4) and Sr[Cr(dpa)(ox)2]2·8H2O (5) [PPh4 = tetraphenylphosphonium cation; AsPh4 = tetraphenylarsonium cation; dpa = 2,2′-dipyridylamine; ox = oxalate dianion; Rad = 2-(4-N-methylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl-3-N-oxide] have been prepared and characterised by single-crystal X-ray diffraction. The structures of 1–4 consist of discrete [Cr(dpa)(ox)2]− anions, tetraphenylphosphonium (1), tetraphenylarsonium (2), monoprotonated Hdpa (3) and univalent radical (4) cations and uncoordinated water molecules (2–4). The chromium environment in 1–4 is distorted octahedral with Cr–O bond distances between 1.982(2)–1.946(2) A and Cr–N bonds of 2.0716(17)–2.048(3) A. The angles subtended at the chromium atom by the two oxalates are 83.6(2)–81.71(8)°, whereas the N–Cr–N angles are 87.76(7)–86.24(9)°. The [Cr(dpa)(ox)2]− unit of 1–4 is also present in 5 but it acts as a chelating ligand through its two oxalato groups towards divalent strontium cations, yielding heterobimetallic zig-zag chains that run parallel to the a axis. Each chain is formed of diamond-shaped units sharing the strontium atoms, while the two other corners are occupied by two crystallographically independent chromium atoms. The [Cr(dpa)(ox)2]− unit in 5 retains the environment observed in 1–4 and the strontium atom is coordinated to eight oxalate oxygens from four oxalate ligands. The two crystallographycally independent chromium centres within each double chain have opposite chirality. However, the adjacent double chains are related by an inversion centre resulting in achiral layers parallel to the ac plane. The magnetic properties of 1–5 have been investigated in the temperature range 1.9–290 K. A quasi Curie law behaviour is observed for 1–3 and 5 in agreement with their crystal structures, whereas a significant antiferromagnetic interaction between the chromium(III) and the radical centre occurs in the case of 4. The synthetic possibilities offered by the use of the heteroleptic species [CrL(ox)2]− (L = α-diimine-type ligand) as a ligand towards metal ions is analysed and discussed in the light of the available structural results.

Structures and Magnetic Properties of [o- and p-MePyNN+]2[Cu(ox)2] (MePyNN+ = Nitronyl Nitroxyl Radical Cation)

Abstract Reactions of [o-MePyNN+]PF6 and [p-MePyNN+]PF6 with [n-Bu4N]2[Cu(ox)2] in acetonitrile yielded dark-blue crystals of [o-MePyNN+]2[Cu(ox)2]·2CH3OH (1) and [p-MePyNN+]2[Cu(ox)2]·2H2O (2), respectively, where [o-MePyNN+] or [p-MePyNN+] represents the 2-(2 or 4-N-methylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazo-1-oxyl 3-oxide radical cation. X-ray structural analyses showed that the crystals of 1 and 2 are isomorphous. The coordination geometry of the Cu2+ ions in 1 and 2 is an elongated octahedron, and the equatorial and apical coordination sites of the Cu2+ ions are occupied by two oxalato groups and two radial cations, respectively. Magnetic susceptibility measurements for 1 and 2 revealed that the copper and radical centers are ferromagnetically coupled with J = +8.2(1) and +7.8(1) cm-1 (H = -2J∑SCu·Srad), respectively.

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.

Synthesis, Crystal Structure, and Magnetic Properties of Oxalato-Copper(II) Complexes with 3,3-Bis(2-imidazolyl)propionic Acid, an Imidazole-Carboxylate Polyfunctional Ligand: From Mononuclear Entities to Ladder-Like Chains.

The synthesis of five new Cu(II) compounds of formula [Cu(HBIP)(C(2)O(4))].H(2)O (1), [Cu(HBIP)(C(2)O(4))(OH(2))].2H(2)O (2), [{Cu(HBIP)Cl}(2)(&mgr;-C(2)O(4))].2H(2)O (3), [{Cu(BIP)}(2)(&mgr;-C(2)O(4))].2H(2)O (4) and [{Cu(BIP)}(2)(&mgr;-C(2)O(4))].6H(2)O (5), together with their spectral and magnetic characterization, is reported. Crystal structures of compounds 2, 3 and 5 have been solved. All these compounds crystallize in the triclinic system, space group P&onemacr;, with a = 7.3322(3) Å, b = 10.014(1) Å, c = 11.541(1) Å, alpha = 113.22(1) degrees, beta = 91.37(1) degrees, gamma = 94.51(1) degrees, Z = 2 for compound 2; a = 7.444(2) Å, b = 8.518(2) Å, c = 11.231(2) Å, alpha = 97.45(2) degrees, beta = 98.99(2) degrees, gamma = 97.95(2) degrees, Z = 1 for compound 3; and a = 7.977(1) Å, b = 8.656(1) Å, c = 11.807(1) Å, alpha = 69.06(1) degrees, beta = 86.07(1) degrees, gamma = 67.36(1) degrees, Z = 1 for compound 5. In compound 2 the asymmetric unit consists of one isolated neutral [Cu(HBIP)(C(2)O(4))(OH(2))] molecule and two noncoordinated water molecules. The Cu(II) ion is five-coordinated (4+1 coordination mode) with HBIP and oxalato entities acting as bidentate ligands and the water molecule as the fifth ligand. The structure of compound 3 is made up of centrosymmetric binuclear [{Cu(HBIP)(Cl)}(2)(&mgr;-C(2)O(4))] units and noncoordinated water molecules. The two copper atoms are linked through a bis-bidentate oxalato group leading to a metal-metal separation of 5.28(3) Å. The coordination stereochemistry of the CuN(2)O(2)Cl chromophore is approximately SP. Compound 5 exhibits a structure built of ladder-like chains. In these chains the rungs are constituted by the neutral dinuclear centrosymmetric [(BIP)Cu(C(2)O(4))Cu(BIP)] entities. The oxalato group bridges two copper atoms in a bis-bidentate fashion, whereas the BIP acts as a tridentate ligand, connecting through their carboxylate groups these dimeric units along the a axis. The copper atom is involved in a five-coordinated CuN(2)O(2)O' chromophore, with a coordination geometry intermediate between SP and TBP. The magnetic properties of all complexes have been investigated. Compound 1 and 2 follow a Curie-Weiss law with very low values of theta. The other three compounds exhibit an antiferromagnetic coupling, with 2J = -265 cm(-)(1) for 3, 2J = -108 cm(-)(1) for 4, and 2J = -5.7 cm(-)(1) for 5. The strength of the exchange interaction is discussed on the basis of the structural features and correlated with published magneto-structural data on similar oxalato-bridged copper(II) compounds.

Calcium Potassium Tris(oxalato-O1,O2)chromate(III) Pentahydrate

The CrIII atom in CaK[Cr(C2O4)3].5H2O, has a regular octahedral geometry with three oxalato groups completing the coordination. Both the calcium and potassium cations are coordinated to the O atom of the oxalate group.

Bis(dicyclohexylammonium) Aquadimethyldi(oxalato-O,O')stannate Ethanol Solvate

The Sn atom in the title compound, [(C6H11)2NH2]2[Sn(C2O4)2(CH3)2(H2O)].C2H6O, is chelated by two isobidentate oxalato groups and it exists in a trans-C2SnO5 pentagonal-bipyramidal environment [C—Sn—C 173.5 (2)°] . The coordinated water molecule is hydrogen bonded to a carbonyl O atom of an adjacent stannate [O⋯O = 2.796 (3) Å] to form a centrosymmetric dinuclear tetraanion. These are linked into sheets through the two ammonium cations [N⋯O 2.783 (3), 2.790 (3), 2.793 (3), 2.848 (3) Å]. The ethanol solvate molecule is hydrogen bonded to another doubly bonded carbonyl O atom [O⋯O = 2.819 (9) Å].

Cr(bipy)(C 2O 4) 2] −—a versatile building block for the design of heteropolymetallic systems 2. Syntheses and crystal structures of [formula omitted] and (AgCr(bipy)(μ-C 2O 4) 2(H 2O) 2) 2 and magnetic properties of the copper(II) derivative

The compounds CuCr 2( bipy) 2(μ- C 2 O 4) 2( H 2 O) 2·1 1 2 H 2 O ( 1) and (AgCr(bipy)(μ-C 2O 4) 2(H 2O) 2) 2 ( 2) have been obtained by self-assembling [Cr(bipy)(C 2O 4) 2] − building blocks with Cu(II) and Ag(I) ions, respectively. The molecular and crystal structures of the two compounds were determined. Crystal 1 is monoclinic, C2/c, a = 20.379(14), b = 11.037(4), c = 17.480(7) A ̊ , β = 124.83(3)° , Z = 4 and R = 0.0369. Its structure consists of discrete linear {CrCuCr} trinuclear species with the copper atom lying on an inversion center. The copper atom exhibits [4 + 2] axially elongated octahedral geometry, the apical positions being occupied by two oxalato oxygen atoms. The CuO bond distances are 1.953(4) (H 2O), 1.998(3) and 2.357(3) Å, the CrO bonds vary from 1.945(3) to 1.982(3) Å, and the CrN bonds are 2.031(4) and 2.054(3) Å. The Cr…Cu distances are 5.288 Å. Crystal 2 is monoclinic, P2 1/ c, a = 14.639(16), b = 15.553(10), c = 16.899(12) A ̊ , β = 114.70(4)°, Z = 4 and R = 0.0629 , and contains discrete tetranuclear cycles formed by two chromium and two silver atoms bridged by the oxalato groups. The silver atoms are penta-coordinated, exhibiting distorted trigonal bipyramidal geometries. The AgO bond distances vary from 2.350(8) to 2.548(7) Å, while the CrO bonds are in the range 1.942(7) to 1.982(6) Å. The magnetic susceptibility data of 1 reveal an irregular spin state structure with S = 5/2 ground state and an antiferromagnetic interaction between the central copper(II) and the chromium(III) atoms ( J = −18.8 cm −1.

μ-Disalicylaldehyde Acyloyl- and Phthaloyldihydrazonato— μ-Oxalatobis(Dioxouranium(VI)) Complexes: Synthesis and Spectral Characterization

Abstract The bis(dioxouranium(VI)) complexes of the composition [(UO2)2 (HLLH)(C2O4)]n 2n H2O of disalicylaldehyde- oxaldyldihydrazone (H4A2) -malonoyldihydrazone (H4A2) -succinoyldihydrazone (H4C2) -glutaroyldihydrazone (H4D2) and -phthaloyldihydrazone (H4E2) have been synthesized. The structural assessment of the complexes has been done on the basis of molar conductance, electronic, infrared, Raman, and 1H nmr spectral studies. The 1H nmr and infrared spectral features of the complexes, on comparison with those of the uncoordinated dihydrazones, indicate that dihydrazones act as dibasic, hexadentate ligands in the keto form coordinating to the uranyl ion through the phenolic oxygen, carbonyl oxygen, and azomethine nitrogen in a bridging fashion. The oxalato group retains its D2h symmetry in the complexes, and is coordinated as a bridging tetradentate ligand to the uranyl ion. The complexes involve eight- coordinated uranium atom.