Transition metal complexes derived from ketone based N(4)-substituted thiosemicarbazones: Crystal structures and spectral studies

Thiosemicarbazones have recently attracted considerable attention due to their ability to form tridentate chelates with transition metal ions through either two nitrogen and sulfur atoms, N–N–S or oxygen, nitrogen and sulfur atoms, O–N–S. Considerable interest in thiosemicarbazones and their transition metal complexes has also grown in the areas of biology and chemistry due to biological activities such as antitumoral, fungicidal, bactericidal, antiviral and nonlinear optical properties. They have been used for metal analyses, for device applications related to telecommunications, optical computing, storage and information processing.The versatile applications of metal complexes of thiosemicarbazones in various fields prompted us to synthesize the tridentate NNS-donor thiosemicarbazones and their metal complexes. As a part of our studies on transition metal complexes with these ligands, the researcher undertook the current work with the following objectives. 1. To synthesize and physico-chemically characterize the following thiosemicarbazone ligands: a. Di-2-pyridyl ketone-N(4)-methyl thiosemicarbazone (HDpyMeTsc) b. Di-2-pyridyl ketone-N(4)-ethyl thiosemicarbazone (HDpyETsc) 2. To synthesize oxovanadium(IV), manganese(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes using the synthesized thiosemicarbazones as principal ligands and some anionic coligands. 3. To study the coordination modes of the ligands in metal complexes by using different physicochemical methods like partial elemental analysis, thermogravimetry and by different spectroscopic techniques. 4. To establish the structure of compounds by single crystal XRD studies

The Synthesis and Coordination Chemistry of Two Families of Polydentate Ligands - Exploring Their Potential for the Preparation of Molecule-Based Magnets

The synthesis and studies of two classes of poly dentate ligands are presented as two projects. In project 1, four new carboxamide ligands have been synthesised via the condensation of 2,2',6,6'-tetrachloroformyl-4,4'-bipyridine or 2,6-dichloroformyl pyridine together with heterocyclic amines containing pyridine or pyrazole substituents. The coordination chemistry of these ligands has been investigated and studies have shown that with a Cu(II) salt, two carboxamide ligands LJ and L2 afford large clusters with stoichiometries [Cu8(L1)4Cl16].CHCl3.5H2O.7CH3OH (I) and [Cu9(L2)6Cl6].CH3OH.5H2O.(C2H5)3N (II) respectively. [molecular diagram availabel in pdf]. X-ray diffraction studies of cluster (I) reveal that it has approximate S4 symmetry and is comprised of four ligands and eight copper (II) centers. Here, coordination takes place via amide 0 atoms, and pyrazole nitrogens. This complex is the first reported example of an octanuclear copper cluster with a saddle-shaped structure. The second cluster comprises nine copper ions that are arranged in a cyclic array. Each ligand coordinates three copper centers and each copper ion shares two ligands to connect six ligands with nine copper ions. The amide nitrogens are completely deprotonated and both amide Nand 0 atoms coordinate the metal centres. The cluster has three-fold symmetry. There are six chloride ions, three of which are bridging two neighbouring Cu(II) centres. Magnetic studies of (I) and (II) reveal that both clusters display weak antiferromagnetic interactions between neighbouring Cu(II) centers at low temperature. In the second project, three complexes with stoichiometries [Fe[N302](SCN)2]2 (III), R,R-[Fe[N3O2](SCN)2 (IV) and R,R-]Fe[N3O2](CN)2] (V) were prepared and characterized, where [N302] is a pentadentate macrocycle. Complex (III) was prepared via the metal templated Schiff-base condensation of 2,2',6,6'-tetraacetyl-4,4'-bipyridine together with 3,6-dioxaoctane-I,8-diamine and comprises of a dimeric macro cycle where the two Fe(II) centres are in a pentagonal-bipyramidal environment with the [N302] ligands occupying the equatorial plane and two axial NCS ligands. Complexes (IV) and (V) were prepared via the condensation of 2,6-diacetylpyridine together with a chiral diamine in the presence of FeCh. The synthetic strategy for the preparation of the chiral diamine (4R,5R)-4,5-diphenyl-3,6-dioxa-I,8-octane-diamine was elucidated. The chirality of both macrocycles (IV) and (V) was probed by circular dichroism spectroscopy. The crystal structure of (IV) at 200 K contains two independent molecules in the unit cell, both of which contain a hepta-coordinated Fe(II) and axial NCS ligands. Variable temperature magnetic susceptibility and structural studies are consistent with a high spin Fe(II) complex and show no evidence of any spin crossover behaviour. In contrast, the bis cyanide derivative (V) crystallizes with two independent molecules in the unit cell, both of which have different coordination geometries consistent with different spin states for the two Fe(II) centres. At 250 K, the molecular structure of (V) shows the presence of both 7- and a 6-coordinate Fe(II) complexes in the crystal lattice. As the temperature is lowered, the molecules undergo a structural change and at 100 K the structural data is consistent with a 6- and 5-coordinate Fe(II) complex in the unit cell. Magnetic studies confirm that this complex undergoes a gradual, thermal, spin crossover transition in the solid state. Photomagnetic measurements indicate this is the first chiral Fe (II) sea complex to exhibit a LIESST.

Spectroscopic and Coordination Behavior of α-Cyanothioacetamide

α-Cyanothioacetamide (CTAM) complexes of cuprous chloride CuCl–2CTAM and cuprous bromide CuBr–2CTAM have been prepared. The infrared spectra of CTAM and its complexes, and the laser Raman spectrum of CTAM have been recorded. Assignment of the frequencies of the ligand has been made on the basis of a normal coordinate analysis using the Urey-Bradley force field. The copper (I) complexes are inferred to have thiocarbonyl sulfur and amide nitrogen bonded CTAM as evidenced from infrared and electronic spectra.

Bonding and correlation analysis of various SiCO isomers

The structural properties for various SiCO isomers in the singlet and triplet states have been investigated using CASSCF methods with a 6-311 +G* basis set and also using three DFT and MP2 with same basis set for those systems except for the linear singlet state. The detailed bonding character is discussed, and the state-state correlations and the isomerization mechanism are also determined. Results indicate that there are four different isomers for each spin state, and for all isomers, the triplet state is more stable than the corresponding singlet state. The most stable is the linear SiCO ((3)Sigma(-)) species and may be refer-red to the ground state. At the CASSCF-MP2(full)/6-311+G* level, the state-state energy separations of the other triplet states relative to the ground state are 43.2 (cyclic), 45.2 (linear SiOC), and 75.6 kcal/mol (linear CSiO), respectively, whereas the triplet-singlet state excitation energies for each configuration are 17.3 (linear SiCO), 2.2 (cyclic SiCO), 10.2 (linear SiOC), and 18.5 kcal/mol (linear CSiO), respectively. SiCo ((3)Sigma(-)) may be classified as silene (carbonylsilene), and its COdelta- moiety possesses CO- property. The dissociation energy of the ground state is 42.5 kcal/mol at the CASSCF-MP2(full)/6-311+G* level and falls within a range of 36.5-41.5 kcal/mol at DFT level, and of 23.7-28.9 kcal/mol at the wave function-correlated level, whereas the vertical IP is 188.8 kcal/mol at the CASSCF-MP2(full)/6-311+G* level and is very close to the first IP of Si atom. Three linear isomers (SiCO, SiOC, and CSiO) have similar structural bonding character. SiOC may be referred to the iso-carbonyl Si instead of the aether compound, whereas the CSiO isomer may be considered as the combination of C (the analogue of Si) with SiO (the analogue of CO). The bonding is weak for all linear species, and the corresponding potential energy surfaces are flat, and thus these linear molecules are facile. Another important isomer is of cyclic structure, it may be considered as the combination of CO with Si by the side pi bond. This structure has the smallest triplet state-singlet state excitation energy (similar to2.2 kcal/mol); the C-O bonds are longer, and the corresponding vibrational frequencies are significantly smaller than those of the other linear species. This cyclic species is not classified as an epoxy compound. State-state correlation analysis and the isomerization pathway searches have indicated that there are no direct correlations among three linear structures for each spin state, but they may interchange by experiencing two transition states and one cyclic intermediate. The easiest pathway is to break the Si-O bond to go to the linear SiCO, but its inverse process is very difficult. The most difficult process is to break the C-O bond and to go to the linear CSiO.

Morphological Adaptations to Drought and Reproductive Strategy of the Moss Syntrichia caninervis in the Gurbantunggut Desert, China

The biological soil crusts (BSCs) in the Gurbantunggut Desert, the largest fixed and semi-fixed desert in China, feature moss-dominated BSCs, which play an indispensable role in sand fixation. Syntrichia caninervis Mitt. (S. caninervis) serves as one of the most common species in BSCs in the desert. In this study we examined the morphological structure of S. caninervis from leafy gametophyte to protonema using light and scanning electron microscopy (SEM). We also examined the relationships between the morphological structure of S. caninervis and environmental factors. We found that: (1) this moss species is commonly tufted on the sand surface, and its leaves are folded upwards and twisted around the stem under dry conditions; (2) the cells on both upper and lower leaf surfaces have C-shaped dark papillae, which may reflect sunlight to reduce the damage from high temperature; (3) the leaf costa is excurrent, forming an awn with forked teeth; and (4) the protonema cells are small and thickset with thick cell walls and the cytoplasm is highly concentrated with a small vacuole. In addition, we also found that the protonema cells always form pouches on the tip of the mother cells during the process of cell polarization. Our results suggest that S. caninervis has, through its life cycle, several morphological and structural characteristics to adapt to dry environmental conditions. These morphological features of S. caninervis may also be found in other deserts in the world due to the world-wide distribution of the species.

Chemical Bonding and Electronic Structure of 4d-Metal Monosulfides

Bond distances, vibrational frequencies, dissociation energies, electron affinities, ionization potentials and dipole moments of the title molecules in neutral and charged ions were studied by use of density functional method. Ground states for each molecule were assigned. The calculated bond distance decreases with the increasing of atomic number of 4d metals, reaches minimum at RhS, then increases. For cationic molecules, the calculated bond distance decreases to the minimum at MoS+, then increases. The calculated vibrational frequency decreases from YS(YS+) to PdS(PdS+) for both neutral and cationic molecules. The bond ionic character decreases from YS(YS+) to PdS(PdS+) for neutral and cationic molecules. The bonding patterns are discussed and compared with the available studies.

Chemical bonding and electronic structure of 4d-metal monocarbides

Bond distances, vibrational frequencies, dissociation energies, electron affinities, ionization potentials and dipole moments of the title molecules in neutral and charged ions were studied by use of density functional method. Ground states for each molecule were assigned. For neutral and cationic molecules, the bond distance decreases from YC (YC+) to RhC (RhC+), then increases, while for anionic molecules, the bond distance decreases from YC- to RuC-, then increases. Opposite trend was observed for vibrational frequency. The bond ionic character decreases from ZrC to PdC for neutral molecules. The bonding patterns are discussed and compared with the available studies.

Extraction and coordination studies of the unexplored bifunctional ligand carbamoyl methyl sulfoxide (CMSO) with uranium(VI) and cerium(III) nitrates. Synthesis and structures of [UO2(NO3)(2)((PhSOCH2CONBu2)-Bu-i)] and [Ce(NO3)(3)(PhSOCH2CONBu2)(2)]

The bifunctional carbamoyl methyl sulfoxide ligands, PhCH2SOCH2CONHPh (L-1), PhCH2SOCH2CONHCH2Ph (L-2), (PhSOCH2CONPr2)-Pr-i (L-3), PhSOCH2CONBu2 (L-4), (PhSOCH2CONBu2)-Bu-i (L-5) and PhSOCH2CON(C8H17)(2) (L-6) have been synthesized and characterized by spectroscopic methods. The selected coordination chemistry of L-1, L-3, L-4 and L-5 with [UO2(NO3)(2)] and [Ce(NO3)(3)] has been evaluated. The structures of the compounds [UO2(NO3)(2)((PhSOCH2CONBu2)-Bu-i)] (10) and [Ce(NO3)(3)(PhSOCH2CONBu2)(2)] (12) have been determined by single crystal X-ray diffraction methods. Preliminary extraction studies of ligand L-6 with U(VI), Pu(IV) and Am(III) in tracer level showed an appreciable extraction for U(VI) and Pu(IV) in up to 10 M HNO3 but not for Am(III). Thermal studies on compounds 8 and 10 in air revealed that the ligands can be destroyed completely on incineration. The electron spray mass spectra of compounds 8 and 10 in acetone show that extensive ligand distribution reactions occur in solution to give a mixture of products with ligand to metal ratios of 1 : 1 and 2 : 1. However, 10 retains its solid state structure in CH2Cl2.

Self-assembled molecular complexes and coordination polymers of CdII, hexamine, and monocarboxylates: structural analysis and theoretical studies of supramolecular interactions

Four new cadmium(II) complexes [Cd-2(bz)(4)(H2O)(4)(mu 2-hmt)]center dot Hbz center dot H2O (1), [Cd-3(bz)(6)(H2O)(6)(mu 2-hmt)(2)]center dot 6H(2)O (2), [Cd(pa)(2)(H2O)(mu(2)-hmt)](n) (3), and {[Cd-3(ac)(6)(H2O)(3)(mu(3)-hmt)(2)]center dot 6H(2)O}(n) (4) with hexamine (hmt) and monocarboxylate ions, benzoate (bz), phenylacetate (pa), or acetate (ac) have been synthesized and characterized structurally. Structure determinations reveal that 1 is dinuclear, 2 is trinuclear, 3 is a one-dimensional (1D) infinite chain, and 4 is a two-dimensional (2D) polymer with fused hexagonal rings consisting of Cd-II and hmt. All the Cd-II atoms in the four complexes (except one CdII in 2) possess seven-coordinate pentagonal bipyramidal geometry with the various chelating bidentate carboxylate groups in equatorial sites. One of the CdII ions in 2, a complex that contains two monodentate carboxylates is in a distorted octahedral environment. The bridging mode of hmt is mu 2- in complexes 1-3 but is mu 3- in complex 4. In all complexes, there are significant numbers of H-bonds, C-H/pi, and pi-pi interactions which play crucial roles in forming the supramolecular networks. The importance of the noncovalent interactions in terms of energies and geometries has been analyzed using high level ab initio calculations. The effect of the cadmium coordinated to hmt on the energetic features of the C-H/pi interaction is analyzed. Finally, the interplay between C-H/pi and pi-pi interactions observed in the crystal structure of 3 is also studied.