Structural elucidation of transition metal complex by single crystal EPR study

Single crystal EPR studies of Mn(II) doped hexaaquazincdiaquabis(malonato) zincate [Zn(H₂O)₆][Zn(mal)₂(H₂O)₂] have been carried out at room temperature using X-band spectrometer to identify the location of the dopant. Single crystal rotations along the three orthogonal axes show more than 30 line pattern EPR spectra indicating the presence of two types of dopant ions in the host lattice, with intensity ratio of 6:1. However, the latter could not be followed due to its low intensity during crystal rotations. The spin-Hamiltonian parameters, estimated from the three mutually orthogonal crystal rotations are: g_xx = 1.972, g_yy = 2.000, g_zz = 2.023, A_xx = 8.95, A_yy = 9.48, A_zz = 9.93 mT, D_xx = −34.49, D_yy = −3.26, D_zz = 37.74 mT and E = 15.6 mT. The direction cosines of one of the principal values of g match with that of Zn-O bond in the host lattice, suggesting that the Mn(II) ion entered the lattice substitutionally. The large value of E is indicative of low symmetry of the substitutional site, in accordance with the crystal structure of the isomorphous [Zn(H₂O)₆][Cu(mal)₂(H₂O)₂]. Covalency of Mn-O bond, estimated from Matamura’s plot, is 9%. Various admixture coefficients, bonding and optical parameters have also been calculated.     

Synthesis of 3-carboethoxy-4,11-dihydro-11-alkyl/phenyl-4-oxopyrimido[1,2-b][1,2,4]benzothiadiazine 6,6-dioxides. A novel heterocyclic ring system

The synthesis of some novel 3-carboethoxy-4,11-dihydro-11-alkyl/phenyl-4-oxopyrimido[1,2-b][1,2,4]benzo-thiadiazine 6,6-dioxides ( IVa-c ) from 3-amino-4-alkyl/phenyl-4H-1,2,4-benzothiadiazine 1,1-dioxides ( 1a-c ) and diethyl ethoxymethylenemalonate ( II ) is described. The compounds have been screened for their antibacterial activity.     

Synthesis,Spectral, Valence‐Bond Parameters,and Single Crystal X‐ray Structural Studies on [Ni(dnpdtc)(PPh3)(NCS)] and [Ni(dnpdtc)(PPh3)(CN)]

Two new nickel complexes withplanar surrounding of Ni [Ni(dnpdtc)(PPh₃)(NCS)] (1) and [Ni(dnpdtc)(PPh₃)(CN)] (2) (dnpdtc=N, N‐dipropyldithiocarbamate) were prepared from the parent dithiocarbamate and were characterized by elemental analysis, electronic, IR and NMR spectra. The structures of both the complexes were determined by single crystal X‐ray crystallography. Thioureide stretching vibrations occur at 1528 cm^‐1 and 1521 cm^‐1 for 1 and 2 respectively. Large ³¹P chemical shifts were observed for the two compounds. A significant asymmetry in Ni—S bond distances was observed in compound 1 [2.1700(16) and 2.2251(17)Å] whereas in compound 2 the bond distances were almost similar [2.2100(14) and 2.2122(13)Å]. A marginal difference was observed with respect to the thioureide bond distances [1.340(6)Å for 1 and 1.312(5)Å for 2 ]. The observation clearly supports the less effective trans influence of SCN^— over PPh₃. However, PPh₃ and CN^— show almost similar trans influence.     

Synthesis, spectral, and single crystal X-ray structural studies on (2,2′-bipyridyl)bis(dimethyldithiocarbamato) zinc(II) and (1,10-phenanthroline) bis(dimethyldithiocarbamato)zinc(II)

Synthesis, spectral, and single crystal X-ray structural studies on (2,2-bipyridyl)bis (dimethyldithiocarbamato)zinc(II) (1) and (l,10-phenanthroline)bis(dimethyldithiocarbamato)zinc(II) (2) complexes are reported in this paper. The complex (1) crystallizes in the orthorhombic lattice, space group Pcca, a = 18.456(3), b = 6.529(2), and c = 17.092(2) Å. The complex (2) crystallizes in the monoclinic space group C2/c, a = 13.372(2), b = 13.850(2), c = 24.680(3) Å, and = 102.71(4)°. IR spectra of the complexes (1) and (2) show the thioureide (C-N) bands at 1489 and 1510 cm^–1, respectively, which are lower than the value observed for the parent bisdithiocarbamate. Reduction in the thioureide stretching frequency is due to the increase in coordination around the zinc ion and the resultant increase in electron density. Thermal studies indicate that the 1,10-phenanthroline adduct is marginally more stable than the other complex. X-ray crystal structures of the two adducts show them to be octahedrally coordinated and monomeric in nature. The Zn-S distances are longer than those observed in the parent bisdithiocarbamate. The thioureide C-N bond distances in (1) and in (2) indicate the partial double bond character. The most important structural changes as a result of the adduct formation are observed in the Zn-S bond distances and S-Zn-S bond angles, in terms of very significant increases in Zn-S bond distances and reductions in S-Zn-S angles, compared to the parent bisdithiocarbamate. The observed changes are indicative of a strong steric force in operation in the adducts rather than electronic effects.     

A single crystal X-Ray diffraction analysis of 1,9-dihydro[1] benzothiopyrano[4,3-c] pyrazole 5,5-dioxide

The structure of 1,4-rlihydro[1 ]benzothiopyrano[4,3-c ]pyrazole 5,5-dioxide was determined by single crystal x-ray diffraction. The molecule crystallizes in space group P2₁/c with a = 13.4378(6), b = 5.5938(3), c = 12.9837(6)Å, and β = 103.831°. The final R value is 0.083. Surprisingly, the tautomer with N(2)-H exists in the crystal with the pyrazole ring being planar. The entire system is not planar as the benzene ring is rotated about C(9a) and C(9b) with respect to the pyrazole ring. In the crystal structure the pyrazole exists as hydrogen-bonded dimers with two molecules related by a center of symmetry.     

Cationic Closo Carboranes—Promising Weakly Coordinating Ions

The unexplored carbon rich cationic closo carboranes, C₃B_n?3H_n⁺¹ (n=5, 6, 7, 10, 12) are investigated theoretically. The position isomers were calculated at the B3LYP/6‐31G* level, and the charge distribution in the cluster is estimated by NBO analysis. The criterion of ring‐cap orbital overlap compatibility along with the number of B? C, C? C, and B? B bonds help in explaining the stability order in each category. The most stable isomer is the one with maximum ring‐cap orbital overlap and largest number of B? C bonds. The order of relative stability among the trigonal bipyramid is 1c > 1b > 1a ′, where the stability is proportional to the number of CH caps over the small three‐membered ring. The C₃B₃H₆⁺ isomer with the one allyl C3 group ( 2b ) is more favorable than the one with a cyclopropenyl group ( 2a ). Among the C₃B₄H₇⁺ isomers the stability order is 3e > 3d > 3c > 3b > 3a , which mostly depends on the ring‐cap orbital overlap. In the bicapped square antiprism (4) where there is large number of isomers, the order follows the rule of ring cap compatibility and the number of B? C bonds. The order of 5e > 5d > 5c > 5b > 5a obtained from the calculations is in perfect agreement with the above sited rules. Equations (1) – (5) devised for estimating the stability of isomers of C₃B_n?3H_n⁺ indicate an increase in stability with cage size. The mono‐positive charge of the isomers is distributed throughout the cage, making them suitable candidates as weakly electrophillic cations. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1542–1551, 2001     

Supramolecular Control of Singlet Oxygen Generation

Singlet oxygen (¹O₂) is the excited state electronic isomer and a reactive form of molecular oxygen, which is most efficiently produced through the photosensitized excitation of ambient triplet oxygen. Photochemical singlet oxygen generation (SOG) has received tremendous attention historically, both for its practical application as well as for the fundamental aspects of its reactivity. Applications of singlet oxygen in medicine, wastewater treatment, microbial disinfection, and synthetic chemistry are the direct results of active past research into this reaction. Such advancements were achieved through design factors focused predominantly on the photosensitizer (PS), whose photoactivity is relegated to self-regulated structure and energetics in ground and excited states. However, the relatively new supramolecular approach of dictating molecular structure through non-bonding interactions has allowed photochemists to render otherwise inactive or less effective PSs as efficient ¹O₂ generators. This concise and first of its kind review aims to compile progress in SOG research achieved through supramolecular photochemistry in an effort to serve as a reference for future research in this direction. The aim of this review is to highlight the value in the supramolecular photochemistry approach to tapping the unexploited technological potential within this historic reaction.     

Quantitative property-property relationship (QPPR) approach in predicting flotation efficiency of chelating agents as mineral collectors

The QPPR approach has been used to model cupferrons as mineral collectors. Separation efficiencies (Es) of these chelating agents have been correlated with property parameters namely, log P , log K oc , substituent-constant σ , Mullikan and ESP derived charges using multiple regression analysis. Es of substituted-cupferrons in the flotation of a uranium ore could be predicted within experimental error either by log P or log K oc and an electronic parameter. However, when a halo , methoxy or phenyl substituent was in para to the chelating group, experimental Es was greater than the predicted values. Inclusion of a Boolean type indicative parameter improved significantly the predictability power. This approach has been extended to 2-aminothiophenols that were used to float a zinc ore and the correlations were found to be reasonably good.