Predicting ESR Peaks in Copper (II) Chelates Having Quadrupolar Coordinating Sites by NMR, ESR and NQR Techniques: A DFT Study (original) (raw)
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ESR Bonding parameter studies of single and mixed ligand complexes of copper (II)
1986
ESR and optical absorption studies are described for a number of copper(II) single and mixed ligand complexes formed with substituted salicylic acids and acetylacetone. ESR spectra of all these complexes give well-resolved spectra in DMF both at room and liquid nitrogen temperatures. The molecular orbital coefficients are estimated assuming an axial symmetry. A partial eovalency is observed in all the single ligand complexes while the in-plane ~r-bonding is as strong as the o-bonding in all the mixed ligand complexes. No regular trend is observed in the value of X (which is proportional to hyperfine constants) with the change in the overall electron withdrawing capacity of the substituent on salicylic acid, either in single ligand or in mixed ligand complexes. However, the X values for all the complexes (except in the case of b/s(acetylsalicylato)copper(II) and (acetylacetonato)-(3,5-dinitrosalicylato)copper(II)) are in agreement with the computed value of X = -3.61 for single crystals of copper-.~cetylacetonate possessing the same environment of four oxygens around copper(II).
European Journal of Inorganic Chemistry, 2003
Dicopper complexes with N,N′-p-xylylenebis(cyclam or cyclen) and with the heteroditopic N,N′-p-xylylenebis(cyclam-cyclen) were synthesized. An X-ray study of the N,N′-p-xylylenebis(cyclen)dicopper complex showed that the copper(II) ion is five-coordinate with an H2O molecule in apical position. With this ligand, a polymeric chain was also obtained in the presence of KSCN. The terminal donor atoms of the bridging NCS− anion are coordinated in apical position to the square-pyramidal copper(II) ion. Two alternating kinds of Cu2L4+ moieties are present in the chain, the first with two N4S chromophores and the second with two N5 chromophores. EXAFS and XANES results are in agreement with a five-coordinate copper ion in the cyclen unit and a six-coordinate copper ion in the cyclam unit. Thermodynamic constants were determined by potentiometry. The existence of dinuclear Cu2L4+ species (ligand/metal ratio < 1) and mononuclear CuLHn(2+n)+ species (ligand/metal ratio > 1) were confirmed by an ESR study at variable pH. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Structural diversity in heteroleptic dipyrrinato copper(II) complexes
Inorganica Chimica Acta, 2014
Synthesis and characterization of the heteroleptic dipyrrinato complexes [Cu 2 (2-pcdpm) 2 (acac) 2 ] (1), [Cu 2 (2-pcdpm) 2 (hfacac) 2 ] (2), [Cu 3 (4-OHdpm) 2 (acac) 4 ] (3), [Cu 3 (4-OHdpm) 2 (hfacac) 4 ] (4), [Cu 2 (3-OHdpm)(acac) 3 ] (5), [Cu 2 (3-OHdpm)(hfacac) 3 ] (6), [Cu(2-OHdpm)(acac)] (7) and [Cu(2-OHdpm)(hfacac)] (8) (acac = acetylacetone; hfacac = hexafluoroacetylacetone; 2-pcdpm = 4-(2-methoxypyridyl)phenyldipyrromethene; 3-pcdpm = 4-(3-methoxypyridyl)phenyldipyrromethene; 4-pcdpm = 4-(4-methoxypyridyl)phenyldipyrromethene; 4-/3-/2-OHdpm = 4-/3-/(2-hydroxyphenyl)dipyrromethene) have been described. The complexes 1-8 have been characterized by elemental analyses, ESI-MS, IR, UV-Vis, EPR and electrochemical (CV and DPV) studies. Electronic absorption spectra of 1-8 clearly suggested that position of the absorption bands depend on the nuclearity and coordination geometry about the copper(II) centres. Structures of 1, 2, 3 and 7 have been determined by X-ray single crystal analyses. The spectral and structural studies revealed that copper(II) in 1 and 2 adopted square pyramidal geometry, whereas in 7 a square planar geometry. On the other hand in trinuclear complex 3 one copper(II) adopted square planar, while other two square pyramidal geometry. In their cyclic voltammograms, 1-6 exhibited an irreversible oxidation and two reduction waves whereas 7 and 8 displayed one oxidation and reduction wave. Variable temperature magnetic susceptibility measurements suggested paramagnetic nature of the complexes 1-3. The X-ray photoelectron spectroscopic (XPS) studies indicated that copper(II) centres in complex 3 are present in two different coordination environments. Room temperature EPR studies on 1-8 (g || > g \ > 2.003) suggested a typical d 9 copper(II) with unpaired electron lying in a d x 2 Ày 2 orbital.
Crystal structure and vibrational spectra of polyamine-copper(II) complexes
Journal of Chemical Crystallography, 1996
The structures of [Cu(en)(H2O)2]SO4 (I), [Cu(en)2](NO3)2 (II) and [Cu(trien)I]I (III) have been determined by single crystal X-ray diffraction. ComplexI is monoclinic, space group C2/c, with unit cell parametera=7.232(1),b=11.725(2),c=9.768(1), β=105.50(1)°, andZ=4. ComplexII is also monoclinic, space group P21/a, witha=7.978(2),b=9.982(4),c=8.218(3), β=111.11(2)°, andZ=2. ComplexIII is orthorhombic, space group P212121, witha=8.098(1),b=11.902(1),c=13.682(2), andZ=4. The structures were solved by direct methods and refined by full-matrix least-squares to finalR values of 0.031, 0.043 and 0.036 for complexesI, II, andIII, respectively. ComplexesI andII show an octahedral coordination geometry. ComplexIII shows a square pyramidal coordination geometry. ComplexI forms infinite monodimensional chains where the SO 4 2− ions acts as a bridge between two neighboringen molecules. The vibrational spectra of these complexes agree well with their crystal structures. Structure and stability of seven other related Cu(II) complexes of (trien), (dien)2, (en)2 and (en) are inferred in this study.
Structure correlation study of four-coordinate copper(I) and (II) complexes
Acta Crystallographica Section B Structural Science, 2000
The geometries of four-coordinate Cu(I) and Cu(II) complexes in the Cambridge Structural Database (CSD) have been analysed systematically and compared using symmetry deformation coordinates and principal component analysis. The observed stereochemistries have been rationalised in terms of the d-electron configurations, interligand repulsion and πbonding effects. The results confirm that the majority of four-coordinate Cu(I) complexes in the CSD adopt tetrahedral geometries, and deviations from tetrahedral symmetry are caused by the presence of chelating ligands or by the incorporation of copper centres into dimeric or polymetallic structures. Four-coordinate Cu(II) complexes generally adopt geometries that are close to square planar; this is particularly evident for bis(chelate) complexes where πbonding is important. Distortions towards tetrahedral geometries are attributable to steric interactions of bulky substituents in the bidentate ligands.
Inorganic Chemistry, 1978
The single-crystal ESR spectra of copper(11)-doped bis(N-methylsalicylaldiminato)zinc(II) and (bis(3-salicylaldiminatopropyl)methylamine)zinc(II) have been recorded. Both the complexes are five-coordinate with geometries intermediate between a square pyramid and a trigonal bipyramid The g and A values of these complexes are discussed on the basis of an angular overlap model. Criteria are suggested for recognizing the ESR spectra of distorted five-coordinate complexes in diluted powders or frozen solutions.