Oxalate Monohydrate Single Crystals Research Articles

Nucleation kinetics, crystal growth and optical studies on lithium hydrogen oxalate monohydrate single crystal

Semi-organic lithium hydrogen oxalate monohydrate non-linear optical single crystals have been grown by slow evaporation solution technique at 40°C. The nucleation parameters such as critical radius, interfacial tension, and critical free energy change have been evaluated using the experimental data. The solubility and the nucleation curve of the crystal at different temperatures have been analyzed. The crystal has a positive temperature coefficient of solubility. The metastable zone width and induction period have been determined for the aqueous solution growth of lithium hydrogen oxalate monohydrate. The UV–vis–NIR spectrum showed this crystal has high transparency. The photoconductivity studies indicate lithium hydrogen oxalate monohydrate has positive photoconductivity behaviour. The low etch pit density observed on ( 0 0 1) crystal surface and the high resolution x-ray difraction analysis indicate the good quality of the grown crystals

Electron spin echo and spin relaxation of low-symmetry Mn2+-complexes in ammonium oxalate monohydrate single crystal

Pulse EPR experiments were performed on low concentration Mn2+ ions in ammonium oxalate monohydrate single crystals at X-band, in the temperature range 4.2–60K at crystal orientation close to the D-tensor z-axis. Hyperfine lines of the resolved spin transitions were selectively excited by short nanosecond pulses. Electron spin echo signal was not observed for the low spin transition (+5/2↔+3/2) suggesting a magnetic field threshold for the echo excitation. Echo appears for higher spin transitions with amplitude, which grows with magnetic field. Opposite behavior displays amplitude of echo decay modulations, which is maximal at low field and negligible for high field spin transitions. Electron spin–lattice relaxation was measured by the pulse saturation method. After the critical analysis of possible relaxation processes it was concluded that the relaxation is governed by Raman T7-process. The relaxation is the same for all spin transitions except the lowest temperatures (below 20K) where the high field transitions (−3/2↔−1/2) and (−5/2↔−3/2) have a slower relaxation rate. Electron spin echo dephasing is produced by electron spectral diffusion mainly, with a small contribution from instantaneous diffusion for all spin transitions. For the highest field transition (−5/2↔−3/2) an additional contribution from nuclear spectral diffusion appears with resonance type enhancement at low temperatures.

Investigations on the growth and characterization of l-citrulline oxalate monohydrate single crystal

New single crystals of l-citrulline oxalate (LCO) monohydrate are grown from aqueous solution by slow evaporation technique. Structure and morphology of the grown crystals are identified by single crystal XRD. The compound crystallizes in the orthorhombic structure with space group P2 12 12 1, having cell parameters, a=5.208(5) Å, b=9.829(5) Å and c=23.879(5) Å. Powder X-ray diffraction data is used for the assignment of the hkl values. The chemical composition of the synthesized crystals is verified by CHN analysis. Functional groups present in the sample are identified by Fourier transform infra red (FT-IR) and FT-Raman spectral analysis. The second harmonic signal generated by the crystal using pulsed Nd: YAG Laser is confirmed by the emission of green radiation, showing that the crystal is a potential candidate for nonlinear optical studies.

EPR and optical absorption studies of vanadyl impurity in lithium hydrogen oxalate single crystal

Electron paramagnetic resonance (EPR) and optical absorption studies of vanadyl ions in lithium hydrogen oxalate monohydrate single crystal and powder are reported at room temperature. Single crystal rotations in each of the three mutually orthogonal crystalline planes, a b ∗ , b ∗ c ∗ and a c ∗ indicate four different vanadyl complexes. The detailed investigation of EPR spectra indicates that one of the VO 2 + sites (the intense one) may enter the lattice substitutionally and the other three occupy the interstitial positions. From the angular variation, the spin Hamiltonian parameters are evaluated and discussed. The optical absorption spectrum shows four bands. From the optical and EPR data, various bonding parameters are determined and the nature of bonding in the crystal is discussed.

Growth aspects of barium oxalate monohydrate single crystals in gel medium

AbstractSingle crystals of barium oxalate monohydrate (BaC2O4.H2O, BOM) were grown in pure form by controlled diffusion of Ba2+ using the gel technique at different temperatures. Starting from aqueous Ba2+ chloride (BaCl2) and acetic acid (C2H2O4) in gel, this method offers a low‐cost and an easiest alternative to other preparation methods for the production of barium oxalate bulky single crystals. The optimal conditions for the growth of BOM crystals in silica gel were found by investigating different growth parameters such as gel pH, gel aging and crystallization temperature. Irrespective of all such crystallization environments, growth rate of the crystals were initially less and then exhibited supersaturation effect leading to non‐linearity. Gel aging and temperature has profound effect on nucleation density that resulted less number of crystals of maximum size in the gel matrix. Perfect single crystals were grown on gels of higher pH. The macropore morphology and porosity was controlled by changing age of the gel. It has been found that temperature has a fabulous effect in controlling the nucleation density by altering the supersaturation conditions for the formation of critical nuclei. The entire growth kinetics informed that the grown crystals were derived by the one dimensional diffusion controlled process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

EPR and optical absorption study of Cr3+-doped ammonium oxalate monohydrate single crystals

Abstract The electron paramagnetic resonance (EPR) study of the Cr 3+ -doped ammonium oxalate monohydrate (AOM) single crystal is done at room temperature. Two magnetically inequivalent sites for chromium are observed. The hyperfine structure for Cr 53 isotope is also obtained. The spin Hamiltonian parameters are evaluated as: D =(309±2)×10 −4 cm −1 , E =(103±2)×10 −4 cm −1 , g =1.9820±0.0002, A =(161±2)×10 −4 cm −1 for site I and D =(309±2)×10 −4 cm −1 , E =(103±2)×10 −4 cm −1 , g =1.9791±0.0002, A =(160±2)×10 −4 cm −1 for site II, respectively. On the basis of EPR data the site symmetry of Cr 3+ doped single crystal is discussed. The optical absorption spectra are recorded in 195–925 nm wavelength range at room temperature. The energy values of different orbital levels are determined. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The values of different parameters are B =803, C =3531, D q =2208 cm −1 , h =0.59 and k =0.21, where B and C are Racah parameters, D q is crystal field parameter and h and k are nephelauxetic parameters, respectively.

In situ study of growth and dissolution kinetics of ammonium oxalate monohydrate single crystals from aqueous solutions containing cationic impurities

AbstractThe results of an in situ investigation of the effect of four different bi‐ and trivalent cations (Fe(III), Cu(II), Mn(II) and Cr(III)) on the displacement velocity of individual growth steps on the (110) face of ammonium oxalate monohydrate crystals as a function of supersaturation are described and discussed. It was observed that: (1) at a particular temperature of pure solutions and solutions containing impurities, the velocity v of movement of the [110] growth steps is always greater than that of the [111] steps, (2) fluctuations in the velocity of individual growth steps occur in all solutions containing similar concentrations of different impurities, (3) the value of kinetic coefficient β for growth steps decreases with an increase in the concentration ci of Cu(II) impurity, but that for dissolution steps does not depend on ci; moreover, the value of kinetic coefficient β for growth steps is higher than that of dissolution steps, and (4) in the presence of Mn(II) and Cr(III) impurities, the kinetic coefficient β for dissolution steps is several times greater than that for growth steps. The results are explained from the standpoint of Kubota‐Mullin model of adsorption of impurities at kinks in the steps and the stability of dominating complexes present in solutions. Analysis of the results revealed that: (1) the effectiveness of different impurities in inhibiting growth increases in the order: Fe(III), Cu(II), Mn(II), and Cr(III), and this behavior is directly connected with the stability and chemical constitution of dominating complexes in saturated solutions, (2) fluctuations in the velocity of growth steps is associated with the effectiveness of an impurity for adsorption; the stronger the adsorption of an impurity, the higher is the fluctuation in step velocity v, and (3) depending on the nature of the impurity, the kinetic coefficient for the dissolution steps can remain unchanged or can be higher than that of the growth steps. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

EPR and optical study of Mn 2+-doped lithium hydrogen oxalate monohydrate single crystals

EPR study of Mn 2+-doped lithium hydrogen oxalate monohydrate single crystals are done at room temperature. The Mn 2+ spin-Hamiltonian parameters are evaluated employing a large number of resonant line positions observed for different orientations of the external magnetic field. The values of g, A , B , D, E and a are 1.9942±0.0002, 114±2×10 −4, 103±2×10 −4, 180±2×10 −4, 57±2×10 −4 and 7±1×10 −4 cm −1, respectively. The optical absorption study of the crystal is also done. The observed bands are assigned as transitions from the 6A 1g(S) ground state to various excited quartet levels of Mn 2+ ion in a cubic crystalline field. These bands are fitted with four parameters, inter-electronic repulsion parameters ( B and C), crystal field parameter ( D q) and Tree's correction ( α). The values found for the parameters are B=814 cm −1, C=2255 cm −1, D q=780 cm −1, and α=76 cm −1. On the basis of the data obtained, the surrounding crystalline field and the nature of metal–ligand bonding are discussed.

Growth kinetics of ammonium oxalate monohydrate single crystals from aqueous solutions containing Co(II) and Ni(II) impurities

AbstractThe growth kinetics of different faces of ammonium oxalate monohydrate (AO) single crystals from aqueous solutions containing different concentrations of Co(II) and Ni(II) ions at a constant temperature are described and discussed. It was found that: (1) at a given supersaturation σ, both Co(II) and Ni(II) ions lead to a decrease in the growth rates R of different faces of AO crystals, (2) the growth of a particular face of the crystals occurs above a critical supersaturation σd, but there is also another supersaturation barrier σ* when the rate abruptly increases with σ, and (3) the values of σd and σ* increase with increasing concentration ci of the impurity. The experimental R(σ) data for different concentrations ci of the impurities were analysed according to the model involving complex source of cooperating screw dislocations and concepts of instantaneous and time‐dependent impurity adsorption. Analysis of the data showed that: (1) adsorption of Co(II) and Ni(II) impurities occurs on the surface terrace of AO crystals, (2) there is a simple relationship between Langmuir constant K and the impurity concentration ci* corresponding to maximum surface coverage, and (3) the ratio σd/σ* of the supersaturation barriers observed in the presence of both impurities increases with an increase in impurity concentration ci, and may be explained from the standpoint of the mechanism of adsorption of impurity particles at kinks and ledges. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Study of segregation coefficient of Mn(II) impurity in ammonium oxalate monohydrate crystals and the relationship between segregation coefficient and growth kinetics

The experimental results of the dependence of effective segregation coefficient keff of Mn(II) impurity in ammonium oxalate monohydrate single crystals during growth from aqueous solutions at a constant temperature on solution supersaturation σ and impurity concentration and the relationship between keff and face growth rates R are described and discussed. Analysis of the results revealed that: (1) the segregation of Mn(II) impurity during crystal growth from solutions is mainly associated with the time-dependent adsorption of impurities and occurs when there is a sudden increase in the growth rate, (2) the time-dependent adsorption takes place when surface coverage by the adsorbed impurity approaches a particular value, (3) keff of an impurity is related with the face growth rate R of the crystals, and (4) the relationship between keff and R can be described by an equation based on the model involving surface coverage due to impurity adsorption and dependence of accumulation and depletion of solvated host molecules at kinks of steps on the F faces of crystals on supersaturation.

Effect of Mn(II) ions on the growth of ammonium oxalate monohydrate crystals from aqueous solutions: II. Growth kinetics

AbstractThe experimental results of the effect of concentration of Mn(II) ions on the growth kinetics of different faces of ammonium oxalate monohydrate single crystals from aqueous solutions at a constant temperature and different predefined supersaturations are described and discussed. It was observed that: (1) at a given supersaturation σ, Mn(II) ions lead to a decrease in the growth rates of different faces of AO crystals, (2) the growth of a particular face of the crystals occurs above a critical supersaturation σd but there is also another supersaturation barrier σ* when the rate abruptly increases with σ, (3) the values of σd and σ* increase with increasing concentration of the impurity, and (4) the values of σd depend on the growth kinetics of a face but those of σ* are independent of face growth kinetics. The experimental R(σ) data for different Mn(II) concentrations ci were analysed according to the model involving complex source of cooperating screw dislocations and concepts of instantaneous and time‐dependent impurity adsorption. It was found that: (1) for a given face the differential heat of adsorption Qdiff is higher during instantaneous impurity adsorption than that during time‐dependent adsorption, and (2) the values of Qdiff involved during instantaneous adsorption are related with face growth kinetics but those during time‐dependent adsorption are independent of face growth kinetics.

Study of segregation coefficient of cationic impurities in ammonium oxalate monohydrate crystals during growth from aqueous solutions

The segregation coefficient k eff of Cu(II), Fe(III) and Cr(III) ions in ammonium oxalate monohydrate single crystals during growth from aqueous solutions at a constant temperature was investigated as a function of solution supersaturation σ and impurity concentration c i. It was observed that: (1) irrespective of the impurity concentration, there is a threshold supersaturation of about 0.03 above which Cr(III) is captured in the crystals but there is no threshold supersaturation in the case of Cu(II) and Fe(III) ions, (2) above the threshold supersaturation, k eff increases with increasing σ and decreasing c i, and (3) at a given σ eff and c i , k eff decreases in the sequence: k eff[Cu(II)] ⪢ k eff[Fe(III)] > k eff[Cr(III)]. The dependence of effective segregation coefficient k eff on supersaturation and impurity concentration is in agreement with the predictions of the model involving surface coverage due to impurity adsorption and dependence of accumulation and depletion of solvated host molecules at kinks of steps on the F faces of crystals on supersaturation [J. Crystal Growth 212 (2000) 522]. Analysis of the effective segregation coefficient k eff of different impurities suggests that the dehydration energies of cations mainly determine the capability of capture of impurity species by the growing crystal.

Incorporation of fluorescent molecules and proteins into calcium oxalate monohydrate single crystals

A central question to understanding biomineralization is determining how biomolecules are integrated within inorganic host lattices, thereby changing material properties yet retaining single crystal structure of the biomineral. We have addressed guest incorporation within single biomineral crystals by investigating face specificity, anisotropy and the role of charges in fluorescent calcium oxalate monohydrate (COM) crystals nucleated from solutions containing eosin Y, fluoresceins and rhodamines. Additionally, we have examined the specificity of incorporation of Protein G wild-type (G-wt) and its mutant (G-Δ6, in which four aspartic acids and two glutamic acids have been replaced by the corresponding asparagine or glutamine), where G-wt promotes and G-Δ6 inhibits COM crystal growth. We found that (1) the negatively charged fluorophores, as well as the fluorophore-labeled proteins, G-wt and G-Δ6, were successfully incorporated during growth into the same {1 1 0} growth sectors in preference to all others; (2) the positively charged TRITC (tetramethyl rhodamine isothiocyanate) was not incorporated as free fluorophore, but it became incorporated if conjugated to G-wt and G-Δ6; (3) once the fluorophores are incorporated, the polarization measurements of adsorption and emission were similar irrespectively whether taken from COM containing the free fluorophores, or the protein conjugates. The anisotropy was similar for rhodamines and fluoresceins.

EPR Spectra of VO2+ Doped Ammonium Oxalate Monohydrate Single Crystals

Abstract The EPR spectra of VO2+ ions in ammonium oxalate monohydrate, [(NH 4)2C2O4-H2O], single crystals have been studied at room temperature and at 113 K in mutually three perpendicular planes. The spin Hamiltonian parameters are determined using a numerical technique together with a trial and error procedure to resolve the single crystal spectra. The parallel and perpendicular components of axially symmetric g and hyperfine tensors for VO2+ ion in ammonium oxalate monohydrate single crystal are determined, and the results are discussed.

EPR and optical absorption spectra of VO2+ ions in calcium oxalate monohydrate single crystals

Electron paramagnetic resonance (EPR) and Optical absorption spectra of vanadyl ions in calcium oxalate monohydrate single crystals have been studied. EPR spectrum at room temperature exhibits an isotropic octet spectrum. The detailed EPR analysis indicates that vanadyl ions exhibit liquid like behaviour. EPR spectrum has been studied at different temperatures. It is found that at 255 K, the EPR spectrum completely disappears. The optical absorption spectrum exhibits three absorption bands characteristic of vanadyl ions in tetragonal symmetry. From the optical data, the crystal field and tetragonal parameters have been evaluated.

EPR of Cu2+-doped potassium oxalate monohydrate single crystal: Jahn-Teller effect and positions of Cu2+ ions

X-band ( approximately 9.5 GHz) EPR measurements on a single crystal of Cu2+-doped K2C2O4.H2O (POM) have been carried out over the temperature interval 4.2-393 K. The data indicate the presence of four magnetically inequivalent Cu2+ sites, consisting of two pairs of physically equivalent sites. A study of the angular variation of the EPR line positions, and the variation of the EPR spectra with temperature reveal that Cu2+ ions belonging to one physically equivalent pair of sites exhibit pseudo-static and dynamic Jahn-Teller effects below and above 172 K, respectively, indicating that their local environment is nearly octahedral. The Cu2+ ions belonging to the other pair of physically equivalent sites do not exhibit a Jahn-Teller effect. An attempt has been made to determine the positions of the Cu2+ ions in the unit cell of POM. The principal values of the g and A matrices, as well as the orientations of their principal axes, for the two sets of physically equivalent Cu2+ ions, are evaluated from the positions of the allowed EPR hyperfine lines at 295, 77 and 4.2 K. In addition, the spin-lattice relaxation times of the Cu2+ ion in POM have been estimated from the EPR linewidths at various temperatures.