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)2SiF6 (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 chain-like crystal structure of 1 is built up of [Cu(en)2]2+ complex cations linked by bridging μ2-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 CuN1 bonds of 1.9994(14) Å (4x), while the axial positions are occupied by fluorine atoms from SiF62− anions with CuF2 bond of 2.6065(14) Å (2x). The individual chains are linked by NH···F type hydrogen bonds. In 2 the coordination polyhedron of the Cu(II) atom can be described as slightly deformed square pyramid (τ = 13.0%) with four N atoms from two chelate dmen ligands placed in the basal plane (CuN bonds are from the range 2.0164–2.0599 Å) while the apical position is occupied by an aqua ligand at CuO distance is 2.293 (2) Å. The structure of 2 is stabilized by OH···F and NH···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/kB = −0.85 K was found in 1. Much stronger exchange coupling J/kB = −3.69 K present in 2 allowed us to identify spatial anisotropy of the exchange coupling, α = 0.2, and to describe 2 by rectangular antiferromagnetic lattice model.