Anangamohan Panja

Synthesis, crystal structures and magnetic properties of 1D polymeric [MnIII(salen)N3] and [MnIII(salen)Ag(CN)2] complexes

The syntheses, crystal structures and variable temperature (5–300 K) magnetic susceptibility measurements of two salen complexes of manganese(III) [where H2salen = N,N′-bis(salicylidene)-1,2-diaminoethane] having azido and dicyano argentate(I) as bridging ligands are reported. Both complexes belong to one-dimensional systems in which the azido functions as μ-(1,3) and Ag(CN)2− as ⋯NC– Ag–CN⋯ bridging ligands. The azido-bridged compound is antiferromagnetic with an intrachain interaction constant J = −4.52(4) cm−1 (Weng model) or J = −5.19(8) cm−1 (Fisher model), and it is a candidate to observe the Haldane gap in a S = 2 system. The silver cyanide bridged complex shows single ion behaviour of the Mn(III) ion, perhaps in combination with a very weak antiferromagnetic interaction.

Syntheses, Structures, and Magnetic Properties of a Novel mer-[(bbp)FeIII(CN)3]2– Building Block (bbp: bis(2-benzimidazolyl)pyridine dianion) and Its Related Heterobimetallic Fe(III)–Ni(II) Complexes

A new symmetrical tricyanide building block mer-[Fe(bbp)(CN)3](2-) [1; bbp = bis(2-benzimidazolyl)pyridine dianion] has been prepared and structurally and magnetically characterized. It forms a new low-spin meridionally capped {Fe(III)L(CN)3} fragment with the tridentate bbp ligand. The reaction of 1 with Ni(II) salts in the presence of various ancillary ligands affords several new cyanido-bridged complexes: a trinuclear complex {[Ni(ntb)(MeOH)]2[Fe(bbp)(CN)3][ClO4]2}·2MeOH (2), a tetranuclear compound {[Ni(tren)]2[Fe(bbp)(CN)3]2}·7MeOH (3), and a one-dimensional heterobimetallic system: {[Ni(dpd)2]2[Fe(bbp)(CN)3]2}·9MeOH·3H2O (4) [ntb = tris(2-benzimidazolylmethyl)amine, tren = tris(2-aminoethyl)amine, and dpd = 2,2-dimethyl-1,3-propanediamine]. The structural data shows that 2 is a linear complex in which a central Fe(III) ion links two adjacent Ni(II) ions via axial cyanides, while 3 is a molecular square that contains cyanido-bridged Ni(II) and Fe(III) ions at alternate corners. Complex 4 is a one-dimensional system that is composed of alternating cyanido-bridged Ni(II) and Fe(III) centers. Compounds 2-4 display extensive hydrogen bonding and moderately strong π-π stacking interactions in the solid state. Magnetic studies show that ferromagnetic exchange is operative within the Fe(III)LS(μ-CN)Ni(II) units of 2-4.

Oxygenation of 4-tert-butylcatechol catalysed by a manganese(II) complex: implications for extradiol catechol dioxygenases

An N donor tetradentate manganese complex, [MnII(bispicen)Cl2] (A) [bispicen = N,N′-bis(2-pyridylmethyl)-1,2-ethanediamine)] catalyses the oxidative cleavage of 4-tert-butylcatechol (1) in the presence of O2. The oxygenated products were isolated by t.l.c. and column chromatography and characterised by 1H-, 13C-n.m.r., DEPT, i.r. and u.v.–vis. spectroscopy. The oxygenated products as well as other spectral evidence suggest that the oxygenation occurs via a 4-tert-butylsemiquinone bound complex, [MnII(bispicen)(4-sq)]+ (4-sq = 4-tert-butylsemiquinone). 1H-n.m.r. spectroscopy suggests that the oxygenation follows multiple pathways. Isolation of the products suggests that the oxygenations proceed in an extradiol fashion and a probable mechanism is suggested. Some intradiol cleaved products have also been detected. E.s.r. spectroscopy suggests that manganese(II) is ultimately converted into the manganese(IV) species.

Solvent-Triggered Cis/Trans Isomerism in Cobalt Dioxolene Chemistry: Distinguishing Effects of Packing on Valence Tautomerism

In this article, the synthesis and X-ray crystal structures of two cis/trans isomers of valence tautomeric (VT) cobalt dioxolene compounds are reported. The cis isomer (1) was isolated from the polar protic methanol solvent as a kinetic product, whereas the less polar nonprotic solvent acetone yielded the trans isomer (2). It should be noted that, although some coordination polymers involving cobalt bis(dioxolene) with the cis disposition are known for bridging ancillary ligands, such an arrangement is unprecedented for mononuclear compounds. A careful study of intermocular interactions revealed that the methanol solvent does not have much influence on the crystal growth in 1, whereas acetone forms strong halogen-bonding interactions that are crucial in the solid-state architecture of 2. This behavior can likely be used in crystal engineering to design new organic-inorganic hybrid materials. The energy difference between the two isomers was examined using DFT calculations, confirming that the trans form is in the thermodynamic state whereas the cis isomer is a kinetic product that can be converted into the trans isomer with time. Finally, both isomers exhibit solvent loss at elevated temperatures that is accompanied by a change in magnetic properties, associated with an irreversible valence tautomerism. Our results highlight the crucial role of the solvents for the isolation of cis/trans isomers in cobalt dioxolene chemistry, as well as the distinguishing effects of intermolecular forces and the solid-state packing on VT behavior.

Synthesis and characterization of new manganese(III) complexes having N4O2 donor sets: Study of the X-ray crystal structure of [Mn(5-Br-sal-N-1,4,7,10)]ClO4 and its electron transfer kinetics with sulfur(IV)

A series of manganese(III) complexes with hexadentate Schiff base ligand having N 4 O 2 donor sets have been synthesized. One of them, [Mn(5-Br-sal-N-1,4,7,10)]ClO 4 ( 1 ), has been characterized through X-ray crystallography. In the complex cation of 1 , the manganese is coordinated by the hexadentate 5-Br-sal-N-1,4,7,10 ligand producing a distorted octahedral MnN 4 O 2 geometry with average MnO and MnN (imine), MnN (amine) bond lengths of 1.952(4), 1.988(5) and 2.244(5) A, respectively. The presence of two long MnO and MnN bonds are consistent with Jahn–Teller effects. The electron transfer reactivity of 1 with sulfur(IV) has been studied over a range of pH 2.60–6.00.