Synthesis, X-ray Structure, Single-Crystal EPR and¹H NMR Studies of a Distorted Square Planar Cu(salEen)₂(ClO₄)₂Complex 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.

Towards ionic liquids with tailored magnetic properties: bmim+ salts of ferro- and antiferromagnetic CuII3 triangles

“…To account for this, we considered a series of axial species with g eff|| = 2.19 (for 2) and 2.15 (for 3) and with g eff|| ≥ g eff⊥ ≥ 0.7. Then, the experimental spectra were fitted to the relative weights of these sub-spectra and distributions were obtained according to a previously described procedure 34,39 [40][41][42][43] EPR spectra can help assess the physical meaning of the fits to magnetic susceptibility data. When analysed through this framework, the fits to the magnetic susceptibility data of 2 and 3 implied rather low values for g 0⊥ (see above).…”

Electron paramagnetic resonance study of ternary CuII compounds with glycine and phenanthroline

“…Providing information about interactions acting between molecular subunits is a subject relevant in biology and in materials science. 1 Several types of weak noncovalent interactions such as syn-anti carboxylate bridges, [2][3][4][5] H-bonds, 6,7 cation-π interactions, 8,9 and π-π stacking [10][11][12][13][14] are important to study biological function, and for a large variety of magnetic, electric and optical properties of materials. 15 Ternary complexes of amino acids 16 such as glycine, 17,18 L-methionine, 19 L-tyrosine, L-tryptophan, L-phenylalanine, 20 aspartic acid 21 and others, with the heteroaromatic diamine ligand 1,10-phenanthroline, show these bonds and * For correspondence attracted attention on preparing and characterizing metal organic frameworks.…”

Syntheses and crystal structures of two copper(II) complexes derived from 2-bromo-4-chloro-6-[(2-morpholin-4-ylethylimino)methyl]phenol

“…Schiff-base ligands similar to HL usually coordinate to copper(II) ions through the imine N and phenolate O atoms, forming square-planar coordination [27,28], however, when thiocyanate or azide anions participate in coordination, the amine N of the Schiff-base ligands also coordinates to the copper(II) [29][30][31][32].…”