# Magnetostructural Studies on Ferromagnetically Coupled Copper(II) Cubanes of Schiff-Base Ligands

Mukherjee, Arindam and Raghunathan, Rajamani and Saha, Manas K and Nethaji, Munirathinam and Ramasesha, Suryanarayanasastry and Chakravarty, Akhil R (2005) Magnetostructural Studies on Ferromagnetically Coupled Copper(II) Cubanes of Schiff-Base Ligands. In: Chemistry, 11 (10). pp. 3087-3096.

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## Abstract

Three cubane copper(II) clusters, namely $[Cu_4(HL')_4]$ (1), $[Cu_4L_2(OH)_2]$ (2), and $[Cu_4L_2(OMe)_2]$ (3), of two pentadentate Schiff-base ligands N,N'-(2-hydroxypropane-1,3-diyl)bis(acetylacetoneimine) $(H_3L')$ and N,N'-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine) $(H_3L)$, are prepared, structurally characterized by X-ray crystallography, and their variable-temperature magnetic properties studied. Complex 1 has a metal-to-ligand stoichiometry of 1:1 and it crystallizes in the cubic space group P43n with a structure that consists of a tetranuclear core with metal centers linked by a $\mu_3$-alkoxo oxygen atom to form a cubic arrangement of the metal and oxygen atoms. Each ligand displays a tridentate binding mode which means that a total of eight pendant binding sites remain per cubane molecule. Complexes $[Cu_4L_2(OH)_2]$ (2) and $[Cu_4L_2(OMe)_2]$ (3) crystallize in the orthorhombic space group Pccn and have a cubane structure that is formed by the self-assembly of two ${Cu_2L}^+$ units. The variable-temperature magnetic susceptibility data in the range 300-18 K show ferromagnetic exchange interactions in the complexes. Along with the ferromagnetic exchange pathway, there is also a weak antiferromagnetic exchange between the copper centers. The theoretical fitting of the magnetic data gives the following parameters: $J_1$ = 38.5 and $J_2 = -18 cm^-^1$ for 1 with a triplet (S = 1) ground state and quintet (S = 2) lowest excited state; $J_1$ = 14.7 and $J2 = -18.4 cm^-^1$ for 2 with a triplet ground state and singlet (S = 0) lowest excited state; and $J_1$ = 33.3 and $J2 = -15.6 cm^-^1$ for 3 with a triplet ground state and quintet lowest excited state, where $J_1$ and $J_2$ are two different exchange pathways in the cubane ${Cu_4O_4}$ core. The crystal structures of $2 \cdot 6 H_2O$ and $3 \cdot 2 H_2O \cdot THF$ show the presence of channels containing the lattice solvent molecules.

Item Type: Journal Article The Copyright belongs to WILEY-VCH Verlag. copper complexes;cubane complexes;ferromagnetism;magnetic properties;Schiff bases;self-assembly Division of Chemical Sciences > Solid State & Structural Chemistry UnitDivision of Chemical Sciences > Inorganic & Physical Chemistry 02 Mar 2006 19 Sep 2010 04:24 http://eprints.iisc.ernet.in/id/eprint/5644