B.A. Sastry

ESR studies on some five coordinate copper (II) complexes in solutions

ESR and optical absorption studies have been made on four 5‐coordinate copper complexes, namely, Cu (trien) Br2, Cu (trien) (ClO4)2, [Cu (trien) NCS]Bφ4, and Cu (Me6trien) Br2 (where trien and Me6trien stand for triethylylenetetramine and N,N,N′N″,N‴,N‴‐hexamethlytrien, respectively) in solutions to study metal ligand bond nature and different contributions to line widths. The 4s character in the ground state is estimated and is found to influence spin‐Hamiltonian constants, bond parameters, and hyperfine linewidth. The hyperfine linewidth at room temperature is explained using the theory of Wilson and Kivelson.

Investigation of the ESR spectra of Cu2+ in K2Co(SO4)2 · 6H2O

Electron spin resonance studies have been carried out on Cu2+ doped K2Co(SO4)2 · 6H2O at different temperatures. The resolution of the spectrum is found to be maximum at about 210 °K and the electric field symmetry around Cu2+ at this temperature is found to be rhombic having the spin‐Hamiltonian constants, gz = 2.330 ± 0.005, gx = 2.227 ± 0.005, gy = 2.053 ± 0.005, Az ≃ (60 ± 2) × 10−4 cm−1, Ax ≃ (52 ± 2) × 10−4 cm−1, and Ay ≃ (59 ± 2) × 10−4 cm−1. These spin‐Hamiltonian parameters are found to be temperature dependent. The linewidth of the copper hyperfine lines are found to increase with decreasing temperature which is most probably brought about by the superposition of a very broad Co2+ line on Cu2+ hyperfine line.

Coordination compounds of manganese(II) with isoxazole, 3,5-dimethylisoxazole and 3-methyl, 5-phenylisoxazole

Abstract A series of compounds of general formula Mn(L) n X 2 have been prepared where L = isoxazole (isox), 3,5-dimethylisoxazole (3,5-diMeisox), 3-methyl, 5-phenylisoxazole (3-Me, 5-Phisox); 1,2,4; X = Cl, Br, I, SCN. The i.r., E.S.R. and electronic spectra, the magnetic moments and the conductivities of the compounds have been used to elucidate their structure. The ligands are generally bridging N and O-bonded and the complexes are hexacoordinate.

EPR studies on Cu(3-amino, 5-methyl isoxazole)4 (ClO4)2 and Cu(3-amino, 5-methyl isoxazole)4 (NO3)2

EPR studies have been carried out on Cu(3-AMI)4(ClO4)2 and Cu(3-AMI)4(NO3)2[3-AMI = 3-amino, 5-methyl isoxazole] in polycrystalline and solution forms both at room (300 K) and liquid nitrogen temperature to obtain stereochemical information and the nature of the metal-ligand bond. Cu(II) hyperfine lines are obtained in these complexes even at room temperature, which is rare for a non-dilute Cu(II) complex. No ligand hyperfine (LHF) structure from bonded nitrogen is obtained in polycrystalline samples of these complexes at the above temperatures to allow the σ-bond strength to be estimated more accurately. The change in the spectral parameters and resolution at liquid nitrogen temperature (LNT) is negligible. The above parameters obtained in MeCN and pyridine solutions of Cu(3-AMI)4(ClO4)2 obtained at LNT are of comparable magnitude with the polycrystalline values indicating less solvation in these solvents. LHF structure from bonded nitrogens observed on the perpendicular component of the above sample in forzen pyridine solution enabled us to calculate the σ-bond strength more accurately than the other cases. The species formed in the DMF (N, N′-dimethylformamide) solution of Cu(3-AMI)4(NO3)2 is characteristic of a CuO6 chromophore indicating stronger solvation in the above solution. The 4s-character in the ground state of Cu(II) in all the above cases was calculated to determine the relative strengths of axial fields.

Studies on the EPR spectra of Cu(3-methyl, 5-phenyl isoxazole)Br2 and Cu(3,5-dimethyl isoxazole)Br2 in solutions

Abstract EPR and optical absorption studies have been carried out on Cu(3-methyl, 5-phenyl isoxazole) Br 2 and Cu(3,5-dimethyl isoxazole)Br 2 in N,N-dimethylformamide (DMF) and pyridine in order to study the solvent effects on these complexes. The EPR spectrum of the former complex in pyridine at room temperature yielded spectra similar to those of powders, due to anisotropic molecular reorientation in solutions. The spin-Hamiltonian constants in DMF solution of both the complexes indicate the existence of CuO 6 chromophores. The metal-ligand bond parameters are calculated.

EPR studies on copper(II) complexes of 2,2',2″-triamino-triethylamine and its hexamethyl derivative

Abstract This paper presents EPR, and optical absorption studies on [Cu(tren)NCS]SCN and [Cu(Me 6 tren)NCS]SCN in solutions. Expressions derived by Barbucci and Bencini are evaluated. It is shown that the molecular motion of the complexes is anisotropic and nondiffusional.

Spectroscopic properties of copper(II) complexes with 4-chloro, 3,5-dimethylisoxazole

Abstract Some 4-chloro, 3,5-dimethylisoxazole copper(II) complexes have been prepared and characterized by the infrared, electronic, paramagnetic resonance spectroscopy and molar conductivity values. The ligand acts as monodentate N-bonded, the halide complexes are tetrahedral, while the perchlorate derivative is square planar.

EPR studies on some copper(II) complexes of 1,4,7,10-tetra-azadecane and its hexamethyl derivative

Abstract EPR studies have been carried out on solutions of the complexes [Cu(trien)NCS](NO 3 ), [Cu(trien)I]I, [Cu(Me 6 trien)NCS]Bϕ 4 and [Cu(Me 6 trien)](ClO 4 ) 2 , (trien = 1,4,7,10-tetraazadecane; Me 6 trien = hexamethyl trien) in different solvents to investigate the solute-solvent interactions. From calculations of the 4 s contribution in the ground state and bond parameters it is found that the axial bond in [Cu(trien)NCS](NO 3 ) dissolved in pyridine is weaker than that in the other complexes dissolved in different solvents. For the two methylated complexes, in spite of the + I effect of the methyl group, the in-plane copper-nitrogen bonds are found to be weak, which is probably due to the changes in structure caused by methylation.

Solute–solvent interaction studies of some Cu(II) complexes by EPR technique

Abstract Even though many workers have studied solute–solvent interactions of paramagnetic complexes in solutions through the spin-Hamiltonian constants, the attempts made to find a single parameter to study the above are less. From a study on a number of Cu(II) complexes, the authors found that the amount of 4s-character present in the ground state of Cu(II) indicated the nature of the symmetry of the chromophore around Cu(II). In the present investigation six Cu(II) complexes viz. , ( i )[Cu(trien)](ClO 4 ) 2 ,( ii )[Cu(trien)NCS] ClO 4 , ( iii ) [Cu(trien)Br] Br, ( iv ) [Cu(trien)NCS] BPh 4 ,( v ) [Cu(Me 6 trien)NCS] ClO 4 , ( vi )[Cu(Me 6 trien)NCS] SCN (trien = triethylenetetramine;Me 6 trien = hexamethyltrien) in DMF(N,N′-dimethylformamide)solutions are chosen to find the validity of the above procedure. From the calculations, it is found that the ground-state of Cu(II) in the ( iv ) complex is free from 4s contribution indicating planar structure. Whereas in the case of the ( iii ) complex, the ground-state is found to possess 0.95% of 4s character indicating strong axial bond. This 4s character in other cases is found to be less than in the above complex. From these studies it is found that 1% of 4s in the ground-state has reduced isotropic contact term (K) by about 30 MHz. Using this value, the values of K in other complexes are computed and these are found to surprisingly coincide with the values obtained experimentally within 1% error.