Cu(en)2SiF6 and [Cu(dmen)2(H2O)]SiF6 (en=1,2-diaminoethane; dmen = N,N-dimethyl-1,2-diaminoethane): Preparations, crystal structures, spectroscopic properties and hydrogen bonding mediated magnetism

Crystals of Cu(en)(2)SiF6 (en = 1,2-diaminoethane) (1) and [Cu(dmen)(2)(H2O)]SiF6 (dmen = N,N-dimethyl-1,2-diaminoethane) (2) were isolated from aqueous-ethanolic systems Cu2+-en or dmen-SiF62- . The chainlike crystal structure of 1 is built up of [Cu(en)(2)](2+) complex cations linked by bridging mu(2)-SiF62- anions with trans positions of the bridging fluorine atoms. Copper ion exhibits usual distorted octahedral coordination; there are two chelate coordinated en ligands in the equatorial plane with Cu-N1 bonds of l1.9994(14) angstrom (4x), while the axial positions are occupied by fluorine atoms from SiF62- anions with CuAF(2) bond of 2.6065(14) angstrom (2x). The individual chains are linked by N-H center dot center dot center dot F type hydrogen bonds. In 2 the coordination polyhedron of the Cu(II) atom can be described as slightly deformed square pyramid (tau = 13.0%) with four N atoms from two chelate dmen ligands placed in the basal plane (Cu-N bonds are from the range 2.0164-2.0599 angstrom) while the apical position is occupied by an aqua ligand at Cu-O distance is 2.293 (2) angstrom. The structure of 2 is stabilized by O-H center dot center dot center dot F and N-H center dot center dot center dot F hydrogen bonds between complex cations and the hexafluoridosilicate anions. The EPR spectra show the rhombic anisotropy of g-factor in both complexes. Magnetic measurements indicate the presence of two-dimensional antiferromagnetic structure in both complexes. A weak exchange coupling J/k(B) = -0.85 K was found in 1. Much stronger exchange coupling J/k(B) = -3.69 K present in 2 allowed us to identify spatial anisotropy of the exchange coupling, alpha = 0.2, and to describe 2 by rectangular antiferromagnetic lattice model. (C) 2012 Elsevier B.V. All rights reserved.