Crystal structures and magnetic properties of a set of dihalo-bridged oxalamidato copper(ii) dimers

Abstract

A set of four copper(II) complexes, L 1 -X and L 2 -X (X = Cl, Br; L 1 = N-(L-leucine methyl ester)-N'-((2-pyridin-2-yl)methyl)oxalamide and L 2 = N-benzyl-N'-((2-pyridin-2-yl)methyl)oxalamide) have been synthesized and characterized by X-ray structural analysis, electron paramagnetic resonance (EPR) spectroscopy on single crystal and by SQUID magnetization measurements. X-ray diffraction studies show one-dimensional hydrogen bonded networks of dimeric copper(II)-complexes bridged by two halide ions and with the two metal centers 3.44-3.69Å apart. The geometry at each copper(II) atom is ideal or near ideal square pyramidal. EPR and SQUID studies indicate that all complexes exhibit weak antiferromagnetic interactions between the Cu(II) paramagnetic centers, with exchange parameter |J| ∼1 cm −1 . Magneto-structural comparisons among similar dihalo-bridged Cu(II) dinuclear complexes are also provided, and a possible correlation has been established.

Magnetostructural Characterization of Oxalamide Dihalo‐Bridged Copper Dimers: Intra‐ and Interdimer Interactions Studied by Single‐Crystal Electron Spin Resonance Spectroscopy

“…Reaction of ligands L A = N ‐( l ‐alanine methyl ester)‐ N ′‐[(2‐pyridine‐2‐yl)methyl]oxalamide and L V = N ‐( l ‐valine methyl ester)‐ N ′‐[(2‐pyridine‐2‐yl)methyl]oxalamide with CuCl 2 and CuBr 2 in MeOH resulted in crystals of the [CuL A (μ‐Cl)] 2 , [CuL A (μ‐Br)] 2 (which crystallized with two independent molecules in the asymmetric unit), [CuL V (μ‐Cl)] 2 , and [CuL V (μ‐Br)] 2 complexes, which were analyzed by X‐ray single‐crystal diffraction (Figure ). The structures of these complexes are very similar to the structures of the dihalo‐bridged Cu II complexes we previously described . Each Cu II ion has an ideal or approximately ideal square‐pyramidal‐type of geometry, as ascertained by the geometric parameter τ of 0.00–0.20 (Table ), for which perfectly square‐pyramidal geometry is associated with τ =0 .…”

“…Recently, magnetostructural correlations in a set of dihalo‐bridged oxalamide copper(II) dimers were reported . Herein, the presented four newly synthesized complexes have slightly different ligands than those previously reported.…”

“…The ligands prepared from l ‐valine and l ‐alanine and the corresponding Cu complexes were synthesized as previously described . Reagents were purchased from Aldrich or Fluka and were used without further purification.…”

From mononuclear to linear one-dimensional coordination species of copper(ii)–chloranilate: design and characterization

“…The simulated spectra, shown in Fig. 56,57 If we consider all copper ions in the sphere of radius 15Å, the values of the dipolar linewidths are G d $ 5-25 mT. The same parameters were used for the simulation of the spectra at low and room temperatures by taking into consideration only line-broadening effect (ESR lines were broader at higher temperatures).…”

Self‐Complementary Dimers of Oxalamide‐Functionalized Resorcinarene Tetrabenzoxazines

“…As far as hydrogen bond mediated self‐assembly systems are concerned, very little attention have been paid to the oxalamide derivatives, despite their high ability to participate in hydrogen bonding and rigid conformation. Indeed, oxalamide derivatives, due to their self‐complementary hydrogen bonding interactions ability, have been used successfully in materials science, in protein engineering and for designing homo‐ and heterometallic complexes . Compared with the amide group, the oxalamide (‐NH‐CO‐CO‐NH‐) group possesses elegant hydrogen‐bond‐forming capacity between ‐C=O and ‐NH units.…”