Wen Xia Tang

Synthesis, crystal structure and magnetic properties of an isophthalate-bridged manganese(II) chain complex

Abstract An isophthalate-bridged manganese(II) chain complex of the formula [Mn2(bipy)4(m-phth)]n-[ClO4]2n·4nH2O, where bipy is 2,2′-bipyridine and m-phth is isophthalate (dianion of benzene-1,3-dicarboxylic acid), has been prepared and characterized by X-ray crystallography and magnetic measurements. The structure consists of cationic isophthalate-bridged [Mn2(bipy)4(m-phth)]2+ chains, non-coordinated perchlorate anions and water molecules of crystallization. Each isophthalate ligand is bound to four manganese atoms through carboxylase oxygens with the syn-syn bridging mode, affording manganese(II) pairs that are linked by the isophthalate group to yield a one-dimensional chain running along the c-axis. The manganese(II) ion displays a distorted octahedral coordination being linked to four nitrogen atoms of two bipy ligands and two oxygen atoms of two carboxylate groups from two isophthalate ligands. The variable temperature magnetic susceptibility of the title complex in the temperature range 4–300 K has been interpreted in terms of MnII dimer with a molecular field approximation, and the values obtained for J, g(fixed) and zJ′ being −0.98 cm−1, 2.00 and − 0.03 cm−1, respectively, indicating a weakly antiferromagnetic exchange coupling between the MnII ions.

Preparation, crystal structure, magnetic and EPR properties of a heptacoordinated manganese(II) chain of [Mn(bipy) (H2O) (TBD)]n (H2TBD=trans-2-butene diacid, bipy= 2, 2′-bipyridine)

Abstract An infinite zigzag chain manganese(II) complex [Mn(bipy) (H 2 O)TBD)] n (bipy= 2, 2′-bipyridine: H 2 TBD=trans-2-butene diacid) has been prepared and characterized by single-crystal X-ray diffraction, and magnetic measurements. The structure was solved by direct methods and refined by least-squares methods to R ( Rw ) values of 0.031 (0.042). Each TBD is bound to two manganese(II) ions through car☐ylate oxygens, affording the manganese(II) ions bridged by TBD group to yield a infinite chain running along the a axis. The intrachain Mn···Mn separation is 9.05A˚, while the shortest interchain Mn···Mn distance is 5.86A˚. The manganese(II) ion displays a distorted pentagonal bipyramid coordination by virtue of bidentate bipyridine, two car☐ylate groups of two TBD and a H 2 O molecule. The variable temperature magnetic susceptibility of the title complex in the temperature range 3.3–302 K has been interpreted in terms of Heisenberg chain model with a molecular field, the values obtained for J, g and zJ′ being: 0.58 cm −1 , 2.01, and −0.09 cm −1 , respectively, indicating weakly antiferromagnetic intra- and interchain exchange interactions. The x -band EPR spectrum of the complex exhibits a six-line manganese hyperfine pattern centered at g = 2.001, A = 94.5G, together with five “forbidden” hyferfine doublets.

A novel mixed-valence manganese(II,III) complex of [Mn4(sal)4(H2O)4(py)8]n[salH]2n·4npy in an infinite chain (salH2 = salicyclic acid; py = pyridine)

Abstract A novel mixed-valence (II, III) infinite chain manganese complex [Mn4(sal)4(H2O)4(py)8]n[salH]2n·4npy with salicyclate bridging ligands has been prepared and characterized by X-ray crystallography and magnetic spectroscopic measurements. It crystallizes in the triclinic system, space group P 1 with a = 12.248(2), a = 14.045(2), c = 15.606(2) A , α = 94.15(1), β = 92.14(1), γ = 112.03(1)°, Z = 1 and V = 2476.0(6) A 3 . The structure was solved by direct methods (MULTAN) and refined by lest-squares methods to residual R(Rw) values of 0.059(0.064). The structure consists of a mixed-valence (II, III) manganese infinite chain of chemical formula [MN4(sal)4(H2O4(py)8]n2n+ containing a tetranuclear repeat unit, together with 2nsalH− and 4npy. In the chain structure, all Mn(II) and Mn(III) ions bridged by salicylate carboxylate groups in a syn-anti configuration are arranged alternately and are six-coordinate with O4N2 atoms. Both Mn2 and Mn3 are located in symmetric centers. The sal2− groups linking the Mn(II) and MN(III) ions have a μ−η3-bridgin mode. Magnetic susceptibility data have been measured in the temperature range 1.6–301 K. The carboxylate bridge could only mediate a very weak antiferromagnetic exchange interaction and the magnetic behavior is better explained by a single-ion zero-field splitting model. The X-band EPR spectrum of the complex exhibits a six-line manganese hyperfine pattern centered at g = 1.998, A = 97 G.

Synthesis, mollecular structure and magnetic properties of dinuclear copper(II) compelxes bridged by the trans-oxamidato group

Abstract The compounds [Cu(oxpn)Cu(HIm) 2 ](ClO 4 ) 2 (H 2 O) 2 ( 1 ) and Cu(oxpn)Cu(N 3 ) 2 ·2H 2 O ( 2 ), where oxpn is the dianion of N,N′-bis(3-aminopropyl)oxamide and HIm is imidazole, were prepared and characterized by means of X-ray crystallography, magnetic and spectroscopic measurements. The structures consist of molecular Cu 11 Cu 11 units in which the Cu 11 ions are bridged by an oxamidato group in the trans conformation. For 1 , the coordination environment of the copper(II) atom is a distorted square planar in the equatorial plane, with the perchlorate ion and water molecules bonded weakly in axial sites to form a quasi-octahedral geometry. For 2 , the centre copper(II) atom is located in an approximately square planar environment. The singlet-triplet energy gap J was deduced from the temperature dependences of magnetic susceptibility and found to be equal to −341.7 and −360.8 cm −1 for 1 and 2 , respectively, with the Hamiltonian H = − JS 1 S 2 . The EPR spectra of the dinuclear compounds indicate that the zero-field splitting tensor is essentially determined by the dipolar contribution, due to the inefficiency of the oxamidato bridge in transmitting the anisotropic exchange interaction.

Synthesis, crystal structure and properties of [Fe2O(bipy)4C12](ClO4)2 · 0.25CH3CN · 0.25CH30H · 0.25H2O, a μ-Oxo diiron(III) complex

Abstract A μ-Oxo binuclear iron(III) complex [Fe2O(bipy)4C12](ClO4)2 · 0.25CH3CN · 0.25CH30H · 0.25H2O with 2,2′-bipyridine and chlorine anion as terminal ligands has been prepared and characterized by X-ray crystallography, Mossbauer and magnetic spectroscopic measurements. The dimeric cation exhibits typical FeμO bond lengths of 1.786 A and a bridge angle of 167.0° . The Fe … Fe separations are 3.549 A. Magnetic susceptibility data have been measured in the temperature range 75–300 K. The μ-Oxo bridge could mediate a strong antiferromagnetic exchange interaction (J= 115.3 cm−1) between the two Fe(III) centers in high spin states. The data of isomer shift and quadrupole splitting obtained from Mossbauer spectrum are in agreement with the distorted octahedral coordination sphere of Fe(III) sites in high spin states.

Crystal structure and properties of a new five-coordinate manganese superoxide dismutase mimic

Abstract A new five-coordinate manganese(II) complex Mn(NTB)(C 8 H 4 O 4 )·DMF·0.5CH 3 OH·0.5H 2 O, where NTB is tris(2-benzimidazolyl-methyl) amine and C 8 H 4 O 4 2− is the dianion of terephthalic acid, was prepared and characterized by X-ray crystallography. It crystallizes in the tetragonal system, space group l 4 1 / a with a = 28.063(1), c = 22.8680(1) A , Z = 16 and V = 18009(9) A 3 . The structure was solved by direct methods and refined by full-matrix least-squares(on F ) to residual R ( wR ) values of 0.0785 (0.076). The manganese in the complex adopts a distorted trigonal-bipyramidal coordination geometry with an N 4 O ligand donor set and bears structural similarities to the active site of Mn-superoxide dismutase. The X-band electron paramagnetic resonance spectrum of the complex exhibits a six-line manganese hyperfine pattern with g = 2.005, A = 94 G. The electrochemical properties of the complex were studied in DMF by cyclic voltammetry. The complex can catalyse the dismutation of superoxide (O 2 − ) effectively in the riboflavin-methionine-nitro blue tetrazolium assay.

Synthesis, crystal structure and magnetic behavior of a linear trinuclear and an infinite chain mixed valence manganese(II,III) complex

Abstract Two mixed valence manganese(II,III) salicylate complexes [Mn3(sal)2(salH)2(H2O)4(4-Me-py)3][Mn(sal)2(4-Me-py)2]·2 (4-Mepy) (1) and [{Mn2 (sal)2(im)2(CH3OH)4}n][Mn(sal)2(py2)]n (2), where H2sal=salicylic acid, im=imidazole and py-pyridine, have been prepared and characterized by means of X-ray crystallography and magnetic measurements. Complex 1 crystallizes in the monoclinic system, space group C2/c, with a = 36.737(4), b = 10.595(4), c = 28.041(5) A , β = 111.337(9)°, V = 10166(3) A 3 and Z=4, while 2 crystallizes in the triclinic system, space group P1, with a = 9.060(1), b = 10.238(2), c = 15.693(5) A , α = 103.07(2), β = 100.50(2), γ = 109.47(1)°, V = 1283.1(2) A 3 and Z = 1. The structures were solved by direct methods and refined by least-squares methods to R (Rw) values of 0.046 (0.046) and 0.040 (0.042) for 1 and 2, respectively. The structure of 1 is composed of a linear trinuclear mixed valence manganese(II,III,II) cationic unit [Mn3(sal)2(salH)2(H2O)4(4-Me-py)6]+ with two bridging sal2− ligands, a monomeric manganese(III) anionic unit [Mn(sal)2(4-Me-py)2]− and two 4-Me-py molecules. The structure of 2 consists of two distinct ionic units. One of them is a polymeric chain formed by the cationic unit [Mn2(sal)2(im)2(CH3OH)4]+, and in the chain Mn(II) and Mn(III) ions are arranged alternately and bridged with sal2− ligands. The other is a monomeric anionic unit [Mn(sal)2(py2)]−. All Mn ions of the structures are six-coordinate and each sal2− group has a μ−η3-sal bridging mode. The magnetic behavior of the two complexes shows that the salicylate carboxylate bridge mediates a weakly antiferromagnetic exchange interaction.

Synthesis, crystal structure and magnetic properties of dinuclear nickel(II) complexes bridged by oxamides

Abstract Two dinuclear nickel(II) complexes, Ni(obbz)Ni(H 2 O) 4 ·2H 2 O ( 1 ) and Ni (oxen)Ni(en)(SCN) 2 ( 2 ) (en = ethylenediamine), (where obbz and oxen are N,N′-bis(2-aminobenzoato)oxamide and N,N′-bis(2-aminoethyl)oxamide dianions, respectively), were prepared and characterized by X-ray crystallography, magnetic and spectroscopic measurements. For both the dinuclear compounds, one nickel(II) central atom is located in an approximately square planar environment, the other one is in a distorted octahedral geometry. The structures consist of molecular Ni II Ni II units in which the nickel(II) ions are bridged by an oxamidato group in cis conformation. The effective moments of both complexes correspond to a high-spin (S = 1) nickel(II) ion at room temperature but decrease rapidly below 14 K. Analysis of the data showed the decrease to correspond to the effects of single ion anisotropy, and the susceptibility of Ni(obbz)Ni(H 2 O) 4 ·2H 2 O ( 1 ) can be described as resulting from the single-ion anisotropy parameter D = 5.54 cm −1 , with the m s = 0 singlet ground state for this complex.

Crystal structure and magnetic properties of two two-dimensional sheet-like polynuclear copper complexes with bridging trans-oxamidate and 4,4′-bipyridine or pyrimidine

Two two-dimensional complex polymers [Cu2L(4,4′-bipy)2]n[ClO4]2n1 and [Cu2L′(pym)2]n[ClO4]2n2, where H2L =N,N′-bis(2-aminoethyl)oxamide, H2L′=N,N′-bis(2-aminopropyl)oxamide, 4,4′-bipy = 4,4′-bipyridine and pym = pyrimidine, have been synthesised, and characterized by crystallographic, spectroscopic and magnetic methods. Both compounds crystallize in the monoclinic system, space group P21/c and Z= 4, with a= 6.859(1), b= 20.085(4), c= 11.860(4)A and β= 93.56(2)° for 1, and a= 8.721(2), b= 8.679(2), c= 16.741(2)A and β= 98.59(1)° for 2. The structures of the two compounds consist of layers of two-dimensional networks along the a-axis. Within each layer, trans-oxamidato-bridged copper(II) dimers asymmetrically connected by 4,4′-bipyridine or pyrimidine extend along bc plane to form an infinite network. The copper(II) has a square-pyramidal co-ordination geometry with N3O atoms forming the basal plane and a nitrogen atom from 4,4′-bipyridine or pyrimidine occupying the apical position. Both compounds exhibit strong antiferro-magnetic coupling with J=–335 for 1 and –560 cm–1 for 2, owing to the efficiency of the oxamidato bridges in facilitating such coupling between copper(II) ions which are separated by more than 5.2 A.

Magnetic properties and crystal structure of a 1D alternating chain copper(II) compound with bridging fumarate and trans-oxamidate ligands

Abstract The complex polymer [Cu2(oxap)(fum)]n·5nH2O, where oxap and fum are dianions of N,N′-bis(2-aminopropyl)oxamide and of fumarate, respectively, was prepared and characterized by means of X-ray crystallography, magnetic and spectroscopic measurements. The structure of this compound consists of alternating chains of copper(II) ions bridged by both oxap and fumarate ligands. The central copper atom is located in an approximately square planar environment. The compound exhibits strong anti-ferromagnetic coupling with J = −390 cm−1, due to the efficiency of the oxamidato bridge in propagating antiferromagnetic exchange interaction between copper(II) ions which are separated by more than 5.2 A.