B. Natarajan

Site determination of vanadyl impurity in cadmium sodium sulphate hexahydrate: single crystal EPR and optical studies

Electron paramagnetic resonance (EPR) and optical studies of VO(II) doped cadmium sodium sulphate hexahydrate (CSSH) are carried out at room temperature. The EPR spectra, recorded in the three orthogonal planes, indicate that the paramagnetic impurity has entered the lattice site both in substitutional and interstitial positions. The spin Hamiltonian parameters, calculated from the spectra for the two sites, are: site I: gxx=1.984, gyy=1.975, gzz=1.938; Axx=6.56, Ayy=7.50, Azz=18.61 mT; site II: gxx=1.982, gyy=1.978, gzz=1.940; Axx=6.88, Ayy=7.56, Azz=18.57 mT. The EPR spectrum of the powder sample also reveals the presence of two sites in the host lattice, suggesting that the two sites are chemically and magnetically inequivalent. The optical absorption spectrum exhibits three characteristic bands. Crystal field, tetragonal field, admixture coefficients and bonding parameters are evaluated, which suggest that the complex is fairly covalent in nature.

Identification of doped paramagnetic vanadyl impurity in dipotassium diaquabis(malonato-κ2O,O′) zincate dihydrate single crystal using EPR and optical techniques

Single crystal electron paramagnetic resonance (EPR) spectroscopic investigation of VO(II) doped dipotassium diaquabis(malonato-κ2O,O′) zincate dihydrate has been carried out at X-band frequencies at 300 K. Single crystal, rotated along the three orthogonal crystallographic axes, has yielded spin Hamiltonian parameters g and A as g xx =1.978, g yy =1.972, g zz =1.936 and A xx =7.12, A yy =6.73, A zz =18.24 mT, respectively. These spin Hamiltonian parameters reflect a slight deviation from axial symmetry to rhombic, which is explained by the interstitial occupation of vanadyl ions. The isofrequency plots and powder EPR spectrum have been simulated using the calculated spin Hamiltonian parameters. The percentage of metal–oxygen bond has been estimated to be 20%. The admixture coefficients and bonding parameters have also been calculated by combining the EPR data with optical data.

The substitutional occupation of vanadyl ion in diaquamalonatozinc(II)—single crystal EPR and powder optical studies

Room temperature single crystal electron paramagnetic resonance (EPR) studies have been carried out on VO(II) doped diaquamalonatozinc(II) at X-band frequencies. The analysis of the data suggests the position of the vanadyl ion is substitutional replacing zinc ion. The spin Hamiltonian parameters gxx=1.998, gyy = 1.960, gzz=1.924 and Axx=7.40, Ayy=6.63, Azz=18.27 mT indicate that the symmetry around metal ion is no longer axial due to the substitution position of the impurity. The optical spectrum of the powder sample recorded at room temperature indicates three bands and the percentage of covalency of the metal–oxygen bond has been estimated as 22%. The admixture coefficients and bonding parameters have been calculated correlating EPR and optical data.

Effect of Jahn–Teller ion in zinc sodium sulphate hexahydrate: a case of low hyperfine coupling constant for Cu(II) ion

Single crystal electron paramagnetic resonance (EPR) studies of Cu(II) doped zinc sodium sulphate hexahydrate are carried out from room temperature (RT) to 123 K. The RT spectra show unresolved hyperfine lines and hence angular variation studies are also carried out at 123 K to obtain spin Hamiltonian parameters. The spin Hamiltonian parameters calculated from the 123 K spectra are: g 11=2.039; g 22=2.232; g 33=2.394; A 11=5.64 mT; A 22=4.20 mT; and A 33=7.94 mT. The g-matrix values at RT and 123 K have matched fairly well with each other. The low hyperfine value (A 33), obtained at 123 K, has been explained by considering considerable admixture of ground state with excited state and the delocalization of the unpaired spin density onto the ligands. The admixture coefficients of ground state wave function are: a=0.346, b=0.935, c=0.055, d=0.040, e=−0.040, where a and b correspond to admixture coefficients for and , respectively. Angular variation of Cu(II) resonances in the three orthogonal axes shows that the impurity has entered a substitutional site in the host lattice in place of Zn(II). Bonding parameters, κ=0.295, P=245.4×10−4, α2=0.709,α=0.8421 and α′=0.6034, have also been calculated to fully characterize the EPR.

Kinetics of thermal degradation of water borne polyurethane dispersion containing polycaprolactone with either isophorone diisocyanate or metatetramethyl xylene diisocyanate

Water borne polyurethane dispersions synthesized using poly caprolactone–isophorone diisocyanate combination and caprolactone–metatetramethyl xylene diisocyanate combination. Thermal stability of the polyurethane dispersions was studied using thermogravimetric technique. The activation energy of decomposition of these polyurethane dispersions was determined by applying classical kinetic models and isoconversional method. Though the classical kinetic models assume constant activation energy for any reaction, the activation energy determined is in good agreement with that obtained via isoconversional analysis. However, the advantage of isoconversional analysis is highlighted compared to classical kinetic models based on the mechanism delineating capacity of isoconversional analysis. The present work compares the thermal stability of the aqueous polyurethane dispersion formed from poly caprolactone–isophorone diisocyanate with caprolactone–metatetramethyl xylene diisocyanate.

Single-crystal EPR investigation of Mn(II)-doped biomineral cobalt ammonium phosphate hexahydrate: a case of multiple substitutions

Single-crystal electron paramagnetic resonance (EPR) study of Mn(II)-doped cobalt ammonium phosphate hexahydrate has been carried out at room temperature. The impurity shows more than 30 line pattern EPR spectra along the three crystallographic axes, suggesting the existence of more than one type of impurity ion in the host lattice. The spin Hamiltonian parameters, estimated from the three mutually orthogonal crystal rotations, are: site 1: g xx =1.989, g yy =1.994, g zz =1.999; A xx =−8.97, A yy =−9.52, A zz =−9.71 mT; D xx =−8.09 mT, D yy =−6.05 mT, D zz =14.14 mT; site 2: g xx =1.988, g yy =2.009, g zz =2.019; A xx =−9.11 mT, A yy =−9.58 mT, A zz =−9.93 mT; D xx =−6.61 mT, D yy =−6.11 mT, D zz =12.72 mT. The angular variation studies further reveal that the Mn(II) impurities enter the lattice substitutionally. The other Mn(II) sites which are at interstitial locations are difficult to follow due to their low intensity. The variation of zero-field splitting parameter with temperature indicates no phase transition. The observation of well-resolved Mn(II) spectrum at room temperature has been interpreted in terms of ‘host spin-lattice relaxation narrowing’ mechanism.

EPR Investigation Of Mn (II) Probe In Diaquamalonatozinc(II) Single Crystals - Usage In Enrichment Of Dental Cement

Single crystal EPR studies on Cu(II) and VO(II) doped Diaquamalonatozinc(II) are already studied and published. Inorder to understand the effect of Mn(II) in the host lattice Diaquamalonatozinc(II), single crstal EPR studies of Mn(II) doped Diaquamalonatozinc(II) are carried out at room temperature to identify the local structure of the host ion. Angular variation of Mn(II) hyperfine lines in the three orthogonal planes shows the presence of a two sites. The spin-Hamiltonian parameters calculated from the single crystal EPR spectra are: gxx = 1.989, gyy = 1.999, gzz = 2.023; Axx = 8.72, Ayy = 9.28; Azz = 9.34 mT, Dxx = -33.36, Dyy = -7.25, Dzz = 40.61 mT and E = 13.05 mT. The spin-Hamiltonian parameters calculated from the powder EPR spectrum are: g = 1.995, A = 9.25 mT, D = -53.6. The percentage of covalency obtained is around 8.5%.