Oxalate Oxygen Atoms Research Articles

Ammonium di-μ-oxalatotitanate(III) dihydrate: an eight-coordinate, polymeric titanium(III) complex

The preparation, magnetic and spectral properties and crystal structure of ammonium di-μ-oxalatotitanate(III) dihydrate are described. NH 4[Ti(C 2O 4) 2] · 2H 2O, M r = 278.01, hexagonal, P6 222, a = 8.935(3) c = 10.878(4) Å, V = 752.1(7) Å 3, Z = 3; R = 0.045 for 426 absorption-corrected independent reflections and 48 parameters. The crystals are isomorphous with those of ammonium di-μ-oxalatoindate(III) dihydrate. The titanium atoms are coordinated by eight oxalate oxygen atoms in a square-antiprismatic arrangement, and bridging oxalate groups link the coordination polyhedra to form a right-handed spiral structure about 6 2 crystal axes.

Two different (oxalato)(bipyridine)copper(II) complexes in one single crystal. Crystal structures and magnetic properties of [Cu2(bipy)2(H2O)2(C2O4)]X2·[Cu(bipy)(C2O4)](X = NO3–, BF4–or ClO4–)

Three complexes of formula [Cu2(bipy)2(H2O)2(C2O4)]X2·[Cu(bipy)(C2O4)](bipy = 2,2′-bipyridine; C2O42–= oxalate, X = NO3–1, BF4–2 or ClO4–3 have been synthesised and their crystal structures determined by single-crystal X-ray diffraction methods at room temperature. They are all isostructural and crystallize in the monoclinic system, space group C2/c, Z= 4, with a= 21.739(2), b= 10.458(1), c= 16.023(2)A, β= 95.69(1)° for 1, a= 22.740(5), b= 10.508(1), c= 16.129(2)A, β= 92.32(1)° for 2, and a= 22.819(3), b= 10.583(2), c= 16.389(2)A, β= 91.52(2)° for 3. The crystal structures of 1 and 2 were determined from Patterson and Fourier analysis and refined by full-matrix least-squares techniques, whereas that of 3 was solved by direct methods. Final values of the reliability factors R(R′) were 0.029 (0.051) for 1, 0.033 (0.046) for 2 and 0.057 (0.059) for 3 with 3290, 3526 and 1972 observed reflections respectively. Their structures consist of cationic centrosymmetric dinuclear [Cu2(bipy)2(H2O)2(C2O4)]2+ units, neutral axiosymmetric mononuclear [Cu(bipy)(C2O4)] entities and either NO3–, BF4– or ClO4– as counter ion. Each copper atom of the dinuclear species is in a square-pyramidal environment with two oxalate oxygen and two bipyridine nitrogen atoms as a base and a water molecule at the apical position. The copper atom of the mononuclear complex is in a slightly tetrahedrally distorted square comprised of two bipyridine nitrogen and two oxalate oxygen atoms. In both complexes one or two more distant atoms of the counter ion completes a (5 + 1) or a (4 + 2) copper co-ordination, respectively. The mono- and di-nuclear entities form an alternating chain via weak interactions through counter ions and copper atoms. Variable-temperature (20–300 K) magnetic susceptibility measurements revealed a strong antiferromagnetic interaction within the dinuclear unit, the singlet–triplet energy gap being –386, –378 and –376 cm–1 for 1, 2 and 3, respectively. The χMT versus T curve for all three complexes exhibits a plateau at T < 80 K which corresponds to the Curie law expected for the mononuclear complex. The magnitude of the exchange coupling in this series has been analysed in the framework of a simple orbital model.

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 structures of µ-oxalato-di[bisethylenediamine-nickel(II)] dinitrate, µ-oxalato-bis[di-(2-aminoethyl)aminecopper(II)] di-perchlorate, and µ-oxalato-bis[di-(3-aminopropyl)aminezinc(II)] diperchlorate

Crystal and molecular structures of the title compounds are reported. In each the complex cation is dimeric with the planar oxalate group acting as a bridge by forming five-membered chelate rings with two metal centres. Co-ordination geometries are approximately octahedral in the nickel compound (I), square pyramidal in the copper compound (II)(oxalate oxygen atoms occupying one basal and one axial site), and trigonal bipyramidal in the zinc compound (III)(oxalate oxygens occupying one apical and one equatorial site). The conformations of the co-ordinated amines are discussed and their relationships with the stereochemistry of the metal centres and with the hydrogen bonding network examined.Crystal data: (I), monoclinic a= 6·33(2), b= 12·03(2), c= 14·95(3)A, β= 91·2(3)°, Z= 2, space group P21/n; (II), orthorhombic. a= 7·02(1), b= 13·25(3), c= 25·27(4)A, Z= 4, space group Pbc2l; (III), orthorhombic, a= 13·38(2), b= 14·72(3), c= 13·30(3)A, Z= 4, space group Pna2l. The structures were solved by the heavy-atom method from photographic data and refined by least squares to R 0·105 [(I), 1936 independent reflexions], 0·101 [(II), 1948], and 0·090 [(III), 1688].

The reactivity of co-ordinated oxalate. Part V. Oxygen-18 exchange studies on the cis-diaquobisoxalatochromate(III) anion

cis-Diaquobisoxalatochromate(III) anion exchanges all eight of its oxalate oxygen atoms with solvent water at the same rate in aqueous acid media at room temperature. Rates and Arrhenius parameters for this reaction are similar to those for the corresponding reaction of the trisoxalatochromate(III) anion.Exchange of the co-ordinated water of both cis- and trans-isomers in aqueous solution is negligible for at least eight days in neutral and acid media at room temperature.