Synthesis, X-ray structure, single-crystal EPR and 1H NMR studies of a distorted square planar Cu(salEen)2(ClO4)2 complex in a novel bilayered architecture: salEen = N,N-diethylethylenesalicylidenamine.

Abstract

Single-crystal X-ray structure and spectroscopic characterizations of Cu(salEen)2(ClO4)2, are reported; salEen is a Schiff base condensation product of equimolar amounts of salicylaldehyde and N,N-diethylethylenediamine. The complex crystallizes in a triclinic space group P1 with a = 12.055(4) A, b = 10.652(3) A, c = 12.701(3) A, alpha = 90.54(2) degrees, beta = 94.39(2) degrees, gamma = 91.35(3) degrees, and Z = 2. The coordination geometry around Cu(II) ion is tetrahedrally distorted square planar with salEen coordinating as a neutral bidentate ligand through N and O donor atoms (average Cu-N and Cu-O distances are 2.004 and 1.880 A, respectively). The counterion ClO4- makes H-bonding contacts with the neighboring cation moieties and forms a one-dimensional layered arrangement of the molecules. The pendent, N,N-diethylethylenediamine groups of salEen (from the centrosymmetrically related molecules) in adjacent layers interpenetrate, forming novel bilayered architectures, which are further held together by pi-pi stacking interactions. EPR studies on single crystals, in three mutually orthogonal planes, yield a rhombic g tensor (gx = 2.041(1), gy = 2.073(1), and gz = 2.220(1)) consistent with the distorted square planar geometry of the CuN2O2 moiety. The peak-to-peak line width of the EPR signal exhibits a |3 cos2 theta - 1|4/3 variation, attributable to one-dimensional magnetic exchange behavior of the complex. The analysis suggests that both the dipole-dipole and exchange interactions contribute to the line width. Interestingly, the complex is amenable for both EPR and NMR studies at ambient temperatures. The proton NMR signals are narrow in CD3CN solutions and the HOMO correlation spectroscopy (COSY) studies reveal the 1H connectivities. Nuclear spin lattice relaxation time (T1) measurements, using inversion recovery method, indicate that T1 values for all the protons are remarkably long compared to those of other mononuclear Cu(II) complexes.