Tarak Nath Mandal

An orthogonal ferromagnetically coupled tetracopper(II) 2 × 2 homoleptic grid supported by µ-O4 bridges and its DFT study

A pyrazole based ditopic ligand (PzOAP), prepared by the reaction between 5-methylpyrazole-3-carbohydrazide and methyl ester of imino picolinic acid, reacts with Cu(NO3)2·6H2O to form a self-assembled, ferromagnetically coupled, alkoxide bridged tetranuclear homoleptic Cu(II) square grid-complex [Cu4(PzOAP)4(NO3)2] (NO3)2·4H2O (1) with a central Cu4[µ-O4] core, involving four ligand molecules. In the Cu4[µ-O4] core, out of four copper centers, two copper centers are penta-coordinated and the remaining two are hexa-coordinated. In each case of hexa-coordination, the sixth position is occupied by the nitrate ion. The complex 1 has been characterized structurally and magnetically. Although Cu–O–Cu bridge angles are too large (138–141°) and Cu–Cu distances are short (4.043–4.131 A), suitable for propagation of expected antiferromagnetic exchange interactions within the grid, yet intramolecular ferromagnetic exchange (J = 5.38 cm−1) is present with S = 4/2 magnetic ground state. This ferromagnetic interaction is quite obvious from the bridging connections (dx2−y2) lying almost orthogonally between the metal centers. The exchange pathways parameters have been evaluated from density functional calculations.

Syntheses, characterization, and X-ray crystal structures of two cis-dioxovanadium(V) complexes of pyrazole-derived, Schiff-base ligands

Two mononuclear cis-dioxovanadium(V) complexes of pyrazole-derived, Schiff-base ligands have been synthesized and characterized. Single crystal X-ray analyses were performed with N ′-[(3-methyl-1H-pyrazole-5-yl)carbonyl]pyridine-2-carbohadrazonamido cis-dioxovanadium(V), {[VO2(PzOAP)] · H2O} (1), and 5-methyl-N-[(1E)-1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3-carbohydrazonate cis-dioxovanadium(V), {[VO2(PzCAP)]} (2). Both complexes crystallize in monoclinic crystal systems with different space groups. Complex 1 crystallizes in the space group P21/c, 2 in space group C2/C. In each complex, the vanadium sits within a distorted square pyramidal geometry with an N2O3 chromophore. The τ parameters of the complexes (0.33 for 1, 0.22 for 2) support their square pyramidal geometry. The interesting finding in the work is that the alkoxide oxygen, imino nitrogen, and pyridine nitrogen take part in the coordination process leaving the pyrazole rings inactive in coordination.