Determination of intermolecular copper–copper distances from the EPR half-field transitions and their comparison with distances from X-ray structures: applications to copper(II) complexes with biologically important ligands

Abstract

An EPR method involving measurement of halffield transitions was applied to determine the intermolecular Cu-Cu distances in copper(II)-carboxylate complexes with biologically important ligands. The experimental powder EPR spectra are composed of allowed (DM S = ±1) transitions centered at *3,200 Gauss and of weak intensity, nominally forbidden, half-field (DM S = ±2) peaks observable at *1,600 Gauss. Values of the average interspin distance for each complex were determined from the ratios of integrated allowed and forbidden peak areas using each of several methods. The calculated interspin distances were correlated with the copper-copper distances experimentally obtained by X-ray crystallography. The distances determined from the EPR spectra agree well with the X-ray determined values when the crystallographic value for one member of a series is used to calibrate the series. Less satisfactory agreement is found when methods based on Cu-spin-label systems are used.

CuSe-based layered compoundBi2YO4Cu2Se2as a quasi-two-d

“…Moreover, the weak resonance signal at 1600 Gauss is often concomitant with the PM resonance signal at 3200 Gauss in the Cu-contained compounds and is termed as half-field transition arising from the formation of a triplet state Cu(II) dimers. 43 As a results, the existence of magnetic ordering and/or spin fluctuation in Bi 2 YO 4 Cu 2 Se 2 can be ruled out based on the present magnetic and EPR results.…”

EPR based distance measurement in Cu-porphyrin–DNA

“…The distance, r, between the paramagnetic centres 33 is given from I rel in eqn (2) with K 0 = 21 (Å 6 ).…”

Structural and spectroscopic characterization of copper(II) tolfenamate complexes

“…X-ray analysis of some copper(II) fenamates (ArCO 2 -) of general formula [Cu 2 (ArCO 2 ) 4 L 2 ], where L is H 2 O, dmf, dmso or caffeine showed, that the copper(II) atoms are bridged in pairs by four fenamate groups to form binuclear molecules [8][9][10][11][12][13][14][15][16][17]. On the other hand, X-ray analysis of some copper(II) fenamates of general formula [Cu(ArCO 2 ) 2 L 2 (H 2 O) n ], where n = 0-2 and L = N,N-dietylnicotinamide, 2-pyridylmethanol, pyridine or imidazole revealed the presence of monomeric complexes with tetragonal-pyramidal or tetragonal-bipyramidal environment about the copper atom [18][19][20][21][22][23][24]. The complexes [Cu(ArCO 2 ) 2 (l-3-pyme) 2 ] n are one-dimensional [25] or two-dimensional coordination polymers [26].…”