title: Self assembled tetranuclear Cu4(II), Ni4(II) [2 × 2] square grids and a dicopper(II) complex of heterocycle based polytopic ligands - Magnetic studies.
abstract: The ditopic ligand PyPzOAP (N-[(Z)-amino(pyridin-2-yl)methylidene]-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazonic acid) and the polytopic ligand 2-PzCAP (N'(3),N'(5)-bis[(1E)-1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3,5-dicarbohydrazide) were synthesized in situ by condensation of methyl imino picolinate with 5-methyl-1-(2-pyridyl) pyrazole-3-carbohydrazide and 2-acetyl pyridine with pyrazole-3,5-dicarbohydrazide respectively. The ligands PyPzOAP and PzOAP (reported earlier, Dalton Trans., 2007, 1229) self-assemble to form homoleptic [2 × 2] tetranuclear M(4) (M = Cu(II) and Ni(II)) square grids structures [Cu(4)(PyPzOAP)(4)](NO(3))(4) (1), [Cu(4)(PzOAP)(4)](ClO(4))(4) (2) and [Ni(4)(PyPzOAP)(4)](NO(3))(4)·8H(2)O·2CH(3)CN (3). While the ligand 2-PzCAP forms a dicopper(II) complex [Cu(2)(2-PzCAP)(OH)(NO(3))(H(2)O)](NO(3))·2H(2)O (4). The complex 1 is a perfect square grid (a = 4.201 Å), whereas, 2 and 3 are almost square grids. All these compounds have been characterized by X-ray structural analyses and variable temperature magnetic susceptibility measurements. EPR studies have also been carried out for complexes 1, 2 and 4. In the Cu(4) grid (1), all the Cu(II) centers are in a distorted octahedral environment with N(4)O(2) chromophore, while, in complex 2, all four Cu(II) centers have a square pyramidal environment with N(3)O(2) chromophore. In complex 3, all four Ni(II) centers have distorted octahedral geometry with N(4)O(2) chromophore. In compound 4, the Cu(II) centers are in square pyramidal environment with N(3)O(2) chromophore. The magnetic properties of compounds 1 and 2 show the presence of intramolecular ferromagnetic exchange interaction (J = 5.88 cm(-1) for 1 and 4.78 cm(-1) for 2). The complex 3 shows weak intramolecular antiferromagnetic interaction (J = -4.02 cm(-1)). While, complex 4, shows strong antiferromagnetic behavior (J = -443 cm(-1)).
authors.affiliation: Department of Chemistry, University College of Science, University of Calcutta, Kolkata, India.
authors.forename: Tarak Nath
authors.initials: TN
authors.lastname: Mandal
authors.forename: Somnath
authors.initials: S
authors.lastname: Roy
authors.forename: Saugata
authors.initials: S
authors.lastname: Konar
authors.forename: Atanu
authors.initials: A
authors.lastname: Jana
authors.forename: Sangita
authors.initials: S
authors.lastname: Ray
authors.forename: Kinsuk
authors.initials: K
authors.lastname: Das
authors.forename: Rajat
authors.initials: R
authors.lastname: Saha
authors.forename: Mohamed Salah
authors.initials: MS
authors.lastname: El Fallah
authors.forename: Ray J
authors.initials: RJ
authors.lastname: Butcher
authors.forename: Sudipta
authors.initials: S
authors.lastname: Chatterjee
authors.forename: Susanta Kumar
authors.initials: SK
authors.lastname: Kar