title: Magnetostructural studies on ferromagnetically coupled copper(II) cubanes of Schiff-base ligands.
abstract: Three cubane copper(II) clusters, namely [Cu(4)(HL')4] (1), [Cu4L2(OH)2] (2), and [Cu4L2(OMe)2] (3), of two pentadentate Schiff-base ligands N,N'-(2-hydroxypropane-1,3-diyl)bis(acetylacetoneimine) (H3L') and N,N'-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine) (H3L), 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 [Cu4L2(OH)2] (2) and [Cu4L2(OMe)2] (3) crystallize in the orthorhombic space group Pccn and have a cubane structure that is formed by the self-assembly of two {Cu2L}+ 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: J1 = 38.5 and J2 = -18 cm(-1) for 1 with a triplet (S = 1) ground state and quintet (S = 2) lowest excited state; J1 = 14.7 and J2 = -18.4 cm(-1) for 2 with a triplet ground state and singlet (S = 0) lowest excited state; and J1 = 33.3 and J2 = -15.6 cm(-1) for 3 with a triplet ground state and quintet lowest excited state, where J1 and J2 are two different exchange pathways in the cubane {Cu4O4} core. The crystal structures of 2 * 6 H2O and 3 * 2 H2O * THF show the presence of channels containing the lattice solvent molecules.
authors.affiliation: Department of Inorganic and Physical Chemistry, Indian Institute of Science, Sir C. V. Raman Avenue, Bangalore 560 012, India.
authors.forename: Arindam
authors.initials: A
authors.lastname: Mukherjee
authors.forename: Rajamani
authors.initials: R
authors.lastname: Raghunathan
authors.forename: Manas K
authors.initials: MK
authors.lastname: Saha
authors.forename: Munirathinam
authors.initials: M
authors.lastname: Nethaji
authors.forename: Suryanarayanasastry
authors.initials: S
authors.lastname: Ramasesha
authors.forename: Akhil R
authors.initials: AR
authors.lastname: Chakravarty
mesh_terms: D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008024:Ligands; D008280:Magnetics; D008958:Models, Molecular; D015394:Molecular Structure; D012545:Schiff Bases / Q000737:chemistry
chemical_list: D008024:Ligands; D012545:Schiff Bases; D003300:Copper