Xiang Shi Tan

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, 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, structure and magnetic properties of a new manganese(III) dimer [Mn2(μ-OCH3)2 (SAL)2(CH3OH)4] bridged by two μ-OCH3 groups

Abstract A new binuclear manganese(III) complex, [Mn2(μ-OCH3)2(sal)2(CH3OH)4] (salH2 = salicylic acid) has been prepared and characterized by x-ray crystallography, magnetic and spectroscopic measurements. The crystal structure consists of neutral manganese(III) dimer complexes, in which the two manganese(III) atoms across a Mn⋯ Mn distance of 3.00 A are bridged by two μ-OCH3 anions. Each MnIII additionally contains two trans-CH3OH and a bidentate salicylate ligands. Magnetic susceptibility data have been measured in the temperature range 80–300 K and indicated that an antiferromagnetic spin-exchange interaction operates between a pair of MnIII ions. The magnetic behaviour is better explained by the Heisenberg model, H = 2JS1S2 (−J = 10.33 cm−1).

Synthesis, crystal structure and superoxide dismutase activity of a five-co-ordinated manganese(II) complex

A five-co-ordinate manganese(II) complex [Mn(ntb)(Hsal)][ClO4], where ntb is tris(benzimidazol-2-ylmethyl)amine and Hsal– is the anion of salicyclic acid (H2sal), has been prepared and characterized by X-ray crystallography. The manganese adopts a distorted trigonal-bipyramidal co-ordination geometry with a N4O ligand donor set and bears structural similarities to the active site of manganese superoxide dismutase. The electro-chemical properties of the complex were studied in MeCN by cyclic voltammetry. The complex can catalyse the dismutation of superoxide (O2–) effectively in the riboflavin–methionine–nitro blue tetrazolium assay.

Synthesis, properties and structure of [MnIII(sa1)(bpy)(MeOH)Cl] · MeOH (sal = salicylate, bpy = bipyridyl, MeOH = CH3OH)

Abstract A new mononuclear manganese(III) complex [Mn(sal)(bpy)(MeOH)Cl] · MeOH (sal = salicylate, C 7 H 4 O 3 2− ; bpy = bipyridyl, C 10 H 8 N 2 ) has been prepared and characterized by X-ray diffraction analysis. The Mn III ion displays elongated octahedral coordination with a C] − and a MeOH molecule occupying axial sites, and the equatorial plane defined by two sal O atoms and two bpy N atoms. The magnetism, electronic spectra and electrochemical behaviour of the title complex are reported and discussed.

Synthesis, crystal structure and magnetic properties of a manganese(III) complex with bound water and double hydrogen-bonding bridges

Abstract The new manganese(III) complex {[HimH]+[Mn(sal)2(py)H2O]−}2 (sal = salicylate, C7H4O3; py - pyridine, C5H5n; [HimH]+ = imidazole cation, C3H5N2) has been prepared and characterized by X-ray analysis and magnetic measurements. The structure of the title complex consists of imidazole cations and two types of mononuclear MnIII complex anions of [Mn(1)(sal)2(py)(H2O)]− and [Mn(2)(sal)(py)(H2O)]−. Each manganese(III) ion display elongated octahedral geometry with water and pyridine molecules occupying axial sites. The equatorial plane is defined by four oxygen atoms from salicylates. Each MnIII complex units is linked to its neighbors above and below by pairs of OwH…O hydrogen bonds between bound water and two noncoordinating carboxylate oxygens of salicylates of the adjacent MnIII units forming an infinite chain running parallel to the crystallographic c-axis. The two types of chains are cross-linked by NH…O hydrogen bonds with imidazolium bridges. The magnetic properties of the title complex are reported and discussed.