Arindam Mukherjee

A new family of octanuclear Cu4Ln4 (Ln = Gd, Tb and Dy) spin clusters

The reaction of Cu(OAc)2 and Ln(OAc)3 (Ln = Gd, Tb and Dy) with 2-amino-2-methyl-1,3-propanediol (ampdH2) under solvothermal conditions has afforded a new family of isostructural octanuclear Cu4Ln4 complexes with the formula [Cu4Ln4(OAc)12(ampdH)8(OH2)2] (Ln = Gd (1), Tb (2) and Dy(3)) in good yield. Variable temperature magnetic susceptibility measurements reveal weak intramolecular exchange interactions for 1 and 2. Ferromagnetic coupling is observed for 1 and attributed to Cu...Gd interactions. In contrast, the magnetic susceptibility behaviour of 2 arises from a combination of intramolecular exchange interactions and the crystal field splitting of the (7)F6 ground state of the Tb(III) ions.

New family of ferric spin clusters incorporating redox-active ortho-dioxolene ligands.

Seven new di-, tri-, tetra-, and hexanuclear iron complexes that incorporate a polydentate Schiff base and variously substituted catecholate ligands have been synthesized from the trinuclear precursor [Fe(3)(OAc)(3)(L)(3)] (1), where LH(2) = 2-[[(2-hydroxyethyl)imino]phenylmethyl]-phenol. These were isolated as the compounds [Fe(3)(OAc)(Cat)(L)(3)] (2), [Fe(6)(OAc)(2)(Cat)(4)(L)(4)] (3), [Fe(4)(3,5-DBCat)(2)(L)(4)] (4), [Bu(4)N][Fe(4)(OAc)(3,5-DBCat)(4)(L)(2)] (5a, 5(-) is the complex monoanion [Fe(4)(OAc)(3,5-DBCat)(4)(L)(2)](-)), [Fe(4)(OAc)(3,5-DBCat)(3)(3,5-DBSQ)(L)(2)] (6), [Fe(2)(Cl(4)Cat)(2)(L)(LH(2))(H(2)O)] (7), and [Et(3)NH](2)[Fe(2)(Cl(4)Cat)(2)(L)(2)] (8a, 8(2-) is the complex dianion [Fe(2)(Cl(4)Cat)(2)(L)(2)](2-)), where CatH(2) = catechol; 3,5-DBCatH(2) = 3,5-di-tert-butyl-catechol; 3,5-DBSQH = 3,5-di-tert-butyl-semiquinone, and Cl(4)CatH(2) = tetrachlorocatechol. While compounds 2-4, 5a, 7, and 8a were obtained by directly treating 1 with the appropriate catechol, compound 6 was synthesized by chemical oxidation of 5a. These compounds have been characterized by single crystal X-ray diffraction, infrared and UV-visible spectroscopy, voltammetry, UV-visible spectroelectrochemistry, and magnetic susceptibility and magnetization measurements. An electrochemical study of the three tetranuclear complexes (4, 5(-), and 6) reveals multiple reversible redox processes due to the o-dioxolene ligands, in addition to reductive processes corresponding to the reduction of the iron(III) centers to iron(II). A voltammetric study of the progress of the chemical oxidation of compound 5a, together with a spectroelectrochemical study of the analogous electrochemical oxidation, indicates that there are two isomeric forms of the one-electron oxidized product. A relatively short-lived neutral species (5) that possesses the same ligand arrangement as complex 5(-) is the kinetic product of both chemical and electrochemical oxidation. After several hours, this species undergoes a significant structural rearrangement to convert to complex 6, which appears to be largely driven by the preference for the 3,5-DBSQ(-) ligand to bind in a non-bridging mode. Variable temperature magnetic susceptibility measurements for compounds 3, 4, 5a, 6, 7, and 8a reveal behavior dominated by pairwise antiferromagnetic exchange interactions, giving rise to a poorly isolated S = 0 ground state spin for compound 3, well-isolated S = 0 ground state spins for complexes 4, 5(-), 7 and 8(2-), and a well-isolated S = 1/2 ground state spin for complex 6. The ground state spin values were confirmed by low temperature variable field magnetization measurements. The thermal variation of the magnetic susceptibility for compounds 3, 4, 5a, 6, 7, and 8a were fitted and/or simulated using the appropriate Hamiltonians to derive J values that are consistent with magnetostructural correlations that have been reported previously for alkoxo-bridged ferric complexes.

Effect of carboxylate spacers on the supramolecular self-assembly of dicopper(II) Schiff base complexes stabilizing water assemblies of different conformations

Dicopper(II) complexes, namely [Cu2L(O2C–CHCH–C6H4-p-OH)]·2H2O (1·2H2O), [Cu2L(O2C–CH2–C6H4-p-OH)]·2H2O (2·2H2O) and [Cu2L(O2C–CH2CH2–C6H4-p-OH)]·0.5H2O (3·0.5H2O), having different carboxylate ligands with a p-hydroxyphenyl moiety and the pentadentate Schiff base N,N′-1,3-diylbis(salicylaldimino)propan-2-ol (H3L) in its trianionic form, were prepared and structurally characterized by X-ray crystallography. The complexes have a dicopper(II) unit with an alkoxo bridge from the Schiff base and the carboxylate, showing a three-atom bridging mode. The metal centres in a square planar CuNO3 coordination geometry are antiferromagnetically coupled in the asymmetrically double-bridged dicopper(II) core. A significant effect of the –CHCH–, –CH2– and –CH2CH2– spacers of the carboxylate ligands on the formation of different supramolecular structures is observed. Complex [Cu2L(O2C–CHCH–C6H4-p-OH)], 1, forms a helical supramolecular structure due to hydrogen-bonding interactions involving the p-hydroxy group of the phenol from the carboxylate and one phenoxo oxygen atom from the Schiff base. The lattice waters form a helical one-dimensional chain, in which alternate water molecules are anchored to the supramolecular host and the chain propagates along the crystallographic 21 screw axis. Complex 2 forms water aggregates of quasi-linear and pseudo-hexameric cyclic chair conformations involving lattice water molecules, and the previously mentioned para OH group phenoxo oxygen atom. Complex 3·0.5H2O shows the formation of a supramolecular one-dimensional chain structure due to hydrogen-bonding interactions between the p-OH group and the phenoxo oxygen atom. Two such supramolecular structures are linked by hydrogen-bonding interactions involving the lattice water. Differential scanning calorimetry (DSC) of 1·2H2O gives two endotherms at 61.5 and 88.5 °C for the loss of the “free” and the “anchored” water molecules, respectively. The overall change of enthalpy per water molecule is ∼36 kJ mol−1. Complex 2·2H2O shows an endotherm at 131 °C with a shoulder at ∼126 °C. The enthalpy change per water molecule is ∼26 kJ mol−1. The reversibility in loss or addition of lattice water molecules and the corresponding effect on the overall structure is probed by X-ray powder diffraction studies.

Helical supramolecular host with aquapores anchoring alternate molecules of helical water chains

Unprecedented 1D helical chains of hydrogen bonded water molecules, showing both handedness and anchored onto a helical supramolecular host formed from the self assembly of a dicopper(II) complex (1) containing pentadentate Schiff base (L) and p-hydroxycinnamate in 1.2H(2)O, propagate along the crystallographic 2(1)-screw axis and the compound shows two endotherms due to loss of water molecules at 61.5 and 88.5 degrees C in the differential scanning calorimetry giving an overall change of enthalpy value of approximately 36 kJ mol(-1) per water molecule.

Ferrocene Mono- and Di-Sulfonates as Building Blocks in Hydrogen-Bonded Networks

The structure directing influence of a variety of hydrogen-bonding cations on the arrangement of ferrocene mono- and di-sulfonate anions within the crystalline state is reported. The crystal structures of four different networks of composition A[Fe(η5-C5H5)(η5-C5H4SO3)] (A = imidazolium or N-methylimidazolium) and B2[Fe(η5-C5H4SO3)2] (B = imidazolium or pyridinium) are presented. The imidazolium ions are able to act as hydrogen bond bridges in the generation of layer-type structures similar to those found for guanidinium analogues. Secondary bonding interactions exert a powerful structure-directing influence within these networks even though the individual interactions appear to be rather weak.

Encapsulation of paramagnetic 3d1-vanadium(IV) in an antiferromagnetically coupled dodecanuclear copper(II) cage

A mixed metal cluster [Cu12VO5L6] of a pentadentate Schiff base (H3L) containing vanadium(IV) in a dodecanuclear copper(I) cage is prepared by vanadyl templated self assembly of dicopper(II) precursor and the structurally characterized complex shows antiferromagnetic coupling involving copper(II) centers, which leads close to diamagnetism for the Cu(II) cage below 40 K in the presence of an encapsulated paramagnetic 3d1-V(IV) atom.