Chemistry

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Three new transition metal complexes using 2-pyrimidineamidoxime (pmadH2) as multidentate chelating and/or bridging ligand have been synthesized and characterized. The ligand pmadH2 has two potential bridging functional groups [$\mu$-O and $\mu$-(N-O)] and consequently shows several coordination modes. While a polymeric 1D CuII complex [Cu(pmadH2)2(NO3)](NO3) (1) was obtained upon treatment of Cu(NO3)2{\textperiodcentered}3H2O with pmadH2 at room temperature in the absence of base, a high temperature reaction in the presence of base yielded a tetranuclear Cu II-complex [Cu4(pmad)2(pmadH) 2(NO3)](NO3)(H2O) (2). One of the CuII centers is in a square pyramidal environment while the other three are in a square planar geometry. Reaction of the same ligand with an equimolar mixture of both Cu(NO3)2{\textperiodcentered}3H2O and NiCl2{\textperiodcentered}6H2O yielded a tetranuclear heterometallic CuII2NiII2 complex [Cu2Ni2(pmad)2(pmadH)2Cl 2]{\textperiodcentered}H2O (3) containing both square planar (Ni II) and square pyramidal (CuII) metal centers. Complexes 1-3 represent the first examples of polynuclear metal complexes of 2-pyrimidineamidoxime. The analysis of variable temperature magnetic susceptibility data of 2 reveals that both ferromagnetic and antiferromagnetic interactions exist in this complex (J1 = +10.7 cm-1 and J2 = -2.7 cm-1 with g = 2.1) leading to a resultant ferromagnetic behavior. Complex 3 shows expected antiferromagnetic interaction between two CuII centers through -N-O- bridging pathway with J 1 = -3.4 cm-1 and g = 2.08. DFT calculations have been used to corroborate the magnetic results. {\textcopyright} 2010 The Royal Society of Chemistry.

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Dalton Transactions

Use of 2-pyrimidineamidoxime to generate polynuclear homo-/heterometallic assemblies: Synthesis, crystal structures and magnetic study with theoretical investigations on the exchange mechanism

Reaction of formamide with Ni(NO3)2{\textperiodcentered}6H 2O under hydrothermal condition in a mixture of MeOH/H2O forms a two-dimensional formate bridged sheet Ni(HCOO)2(MeOH) 2 (1). X-ray structure analysis reveals the conversion of formamide to formate which acts as a bridging ligand in complex 1 where the axial sites of Ni(II) are occupied by methanol used as a solvent. An analogous reaction in presence of 4,4′-bipyridyl (4,4′-bipy) yielded a three-dimensional structure Ni(HCOO)2(4,4′-bpy) (2). DC magnetic measurements as a function of temperature and field established the presence of spontaneous magnetization with Tc (Curie temperature) = 17 and 20.8 K in 1 and 2, respectively, which can be attributed due to spin-canting. DFT calculations were performed to corroborate the magnetic results of 1 and 2. {\textcopyright} 2010 Elsevier Ltd. All rights reserved.

Polyhedron

A formate bridged Ni(II) sheet and its 3D analogue in presence of a linear organic linker: Synthesis, crystal structure and magnetic properties

The crystal structures and magnetic properties of five new transition metal-azido complexes with two anionic [pyrazine-2-carboxylate (pyzc) and p-aminobenzoate (paba)] and two neutral [pyrazine (pyz) and pyridine (py)] coligands are reported. All five complexes were synthesized by solvothermal methods. The complex [Co2(pyzc)2(N3) 2(H2O)2]n (1) is 1D and exhibit canted antiferromagnetism, while the 3D complex [MnNa(pyzc)(N3) 2(H2O)2]n (2) has a complicated structure and is weakly ferromagnetic in nature. [Mn2(paba) 2(N3)2(H2O)2] n (3), is a 2D sheet and the MnII ions are found to be antiferromagnetically coupled. The isostructural 2D complexes [Cu 3(pyz)2(N3)6]n (4) and [Cu3(py)2(N3)6]n (5) resemble remarkably in their magnetic properties exhibiting moderately strong ferromagnetism. Density functional theory calculations (B3LYP functional) have been performed to provide a qualitative theoretical interpretation of the overall magnetic behavior shown by these complexes. {\textcopyright} 2010 The Royal Society of Chemistry.

A series of transition metal-azido extended complexes with various anionic and neutral co-ligands: Synthesis, structure and their distinct magnetic behavior

With the emerging interest in optical in vivo imaging, there is an increasing demand of photostable near-infrared (NIR) dyes. Herein we report the rational design of an amine tricarbocyanine structure with improved photostability (CyNA) and its combinatorial derivatization to render CyNA-414 as a NIR-fluorescent dye with stronger emission intensity and higher photostability than the NIR standard IndoCyanine Green (ICG). © 2010 The Royal Society of Chemistry.

Chemical Communications

Development of photostable near-infrared cyanine dyes

Treatment of pink titanium(iii) triflate (0.045 M) with HF in triflic acid (CH3SO3H) converts Ti(iii) rapidly to a 1:1 mixture of TiIV and green TiII: (2 TiIII + 4 HF → TiF4 + TiII + 4 H+). This disproportionation is half complete when [HF] added is 0.027 M. Substituted 1,4-benzoquinones are reduced rapidly by Ti(iii) in the absence of fluoride, yielding straightforward logarithmic curves, but reactions of the same quinones with Ti(ii) in fluoride media exhibit more complex profiles, the major portions of which are zero order in oxidant. These reactions are strongly catalyzed by added Ti(iv). Analyses of complex curves are consistent with a reaction sequence initiated by Ti(ii)-Ti(iv) disproportionation, forming Ti(iii), which reacts with the quinone, yielding the quinhydrone, QH. The latter is rapidly reduced by Ti(ii). Values of rate constants obtained from these analyses are in agreement with those for reductions of quinones by Ti(iii), in the absence of fluoride. © The Royal Society of Chemistry 2010.

Hypovalent titanium and Ti(II)-Ti(III) interconversions

Poly(Lactic Acid): Synthesis, Structures, Properties, Processing, and Applications

Design and Synthesis of Different Types of Poly(Lactic Acid)

Experimental charge density distributions in two known conformational polymorphs (orange and yellow) of coumarin 314 dye are analyzed based on multipole modeling of X-ray diffraction data collected at 100 K. The experimental results are compared with the charge densities derived from multipole modeling of theoretical structure factors obtained from periodic quantum calculation with density functional theory (DFT) method and B3LYP/6-31G(d,p) level of theory. The presence of disorder at the carbonyl oxygen atom of ethoxycarbonyl group in the yellow form, which was not identified earlier, is addressed here. The investigation of intermolecular interactions, based on Hirshfeld surface analysis and topological properties via quantum theory of atoms in molecule and total electrostatic interaction energies, revealed significant differences between the polymorphs. The differences of electrostatic nature in these two polymorphic forms were unveiled via construction of three-dimensional deformation electrostatic potential maps plotted over the molecular surfaces. The lattice energies evaluated from ab initio calculations on the two polymorphic forms indicate that the yellow form is likely to be the most favorable thermodynamically. The dipole moments derived from experimental and theoretical charge densities and also from Lorentz tensor approach are compared with the single-molecule dipole moments. In each case, the differences of dipole moments between the polymorphs are identified. © 2010 American Chemical Society.

Crystal Growth and Design

Experimental and theoretical charge density analysis of polymorphic structures: The case of coumarin 314 dye

The performance attained by electronic devices incorporating more than a single molecule is in part limited by weak electronic coupling between molecules. By implementing designed supramolecular interactions, chemists have begun taking control of the nanoscale ordering of the active layer in an effort to move beyond the trial and error tuning of the device morphology. This review describes current progress in solid-state devices in which the molecular components possess designed supramolecular interactions - as opposed to non-specific cohesive forces - used to instill or modify functionality. Supramolecular organic devices for applications in solar energy conversion, light-emitting diodes, field-effect transistors, storage and logic functions are covered. © 2010 Elsevier B.V.

Coordination Chemistry Reviews

Harnessing supramolecular interactions in organic solid-state devices: Current status and future potential

Steady state and time-resolved fluorescence spectroscopic techniques have been used to explore the Stokes shift dynamics and rotational relaxation of a dipolar solute probe in molten mixtures of acetamide (CH3CONH 2) with sodium and potassium thiocyanates (Na /KSCN) at T ∼ 318 K and several other higher temperatures. The dipolar solute probe employed for this study is coumarin 153 (C153). Six different fractions (f) of KSCN of the following ternary mixture composition, 0.75CH3CONH2 + 0.25[(1 - f)NaSCN + fKSCN], have been considered. The estimated experimental dynamic Stokes shift for these systems ranges between 1800 and 2200 cm -1 (±250 cm-1), which is similar to what has been observed with the same solute probe in several imidazolium cation based room temperature ionic liquids (RTIL) and in pure amide solvents. Interestingly, this range of estimated Stokes shift, even though not corresponding to the megavalue of static dielectric constant reported in the literature for a binary mixture of molten CH3CONH2 and NaSCN, exhibits a nonmonotonic KSCN concentration dependence. The magnitudes of the dynamic Stokes shift detected in the present experiments are significantly less than the estimated ones, as nearly 40-60% of the total shift is missed due to the limited time resolution employed (full-width at half-maximum of the instrument response function ∼70 ps). The solvation response function, constructed from the detected shifts in these systems, exhibits triexponential decay with the fastest time constant (τ1) in the 10-20 ps range, which might be much shorter if measured with a better time resolution. The second time constant (τ2) lies in the 70-100 ps range, and the third one (τ3) ranges between 300 and 800 ps. Both these time constants (τ2 and τ3) show alkali metal ion concentration dependence and exhibit viscosity decoupling at higher viscosity in the NaSCN-enriched region. Time dependent rotational anisotropy has been found to be biexponential at all mixture compositions studied. Both the average solvation (〈τs〉) and rotation (〈τr〉) times of C153 in these mixtures exhibit fractional power law dependence on medium viscosity (〈τx〉 ∞ νp, x being solvation or rotation). For solvation, p is found to be 0.46, which is very different from that obtained for common polar and nonpolar solvents, and RTILs (p ≈ 1). For rotation, p ≈ 0.65, which is again different from the value (p ≈ 1) obtained for common polar solvents and RTILs but very similar to that (p ≈ 0.6) found for nonpolar solvents. In addition, experimentally measured average rotation times in these mixtures are found to exhibit slip behavior in the low ν/T region, which gradually transforms to subslip as ν/T increases. Calculations using a recently developed semimolecular theory predict a total dynamic Stokes shift for C153 (dipolar solute) in these molten mixtures near ∼1600 cm-1 where the solute-solvent (dipole-dipole) and the ion-solute (ion-dipole) interactions contribute respectively ∼80% and ∼20% to the calculated total shift. Like in experiments, the theoretically predicted solvation response function in the overdamped limit at each mixture composition has been found to be triexponential. The calculations in the underdamped limit, however, suggest a biphasic decay where a composition independent subpicosecond component and a much slower component with the time constant spreading over 150-850 ps contribute equally to constitute the total decay. The calculated average solvation times in this limit are found to be in better agreement with experimental results than the predictions from the overdamped limit. © 2010 American Chemical Society.

Journal of Physical Chemistry B

Fluorescence spectroscopic studies of (acetamide + sodium/potassium thiocyanates) molten mixtures: Composition and temperature dependence

Research on structure and magnetic properties of polynuclear metal complexes to understand the structural and chemical factors governing the electronic exchange coupling mediated by multi-atom bridging ligands is of growing interest. Hydrothermal treatment of Ni(NO3) 2{\textperiodcentered}6H2O with N-(4-carboxyphenyl)iminodiacetic acid [N-4(H3CPIDA)] at 150 °C yielded a 3D coordination polymer of general formula [Ni3{N-4(CPIDA)}2(H2O) 3]{\textperiodcentered}6H2O (1). An analogous network of general formula [Co3{N-3(CPIDA)}2(H2O) 3]{\textperiodcentered}3H2O (2) was synthesized using N-(3-carboxyphenyl)iminodiacetic acid [N-3(H3CPIDA)] in combination with Co(NO3)2{\textperiodcentered}6H2O under identical reaction condition. Both the complexes contain trinuclear secondary building unit and crystallized in monoclinic system with space groups C2/c (1) and P21/c (2), respectively. Variable temperature magnetic characterization of these complexes in the temperature range of 2-300 K indicated the presence of overall ferromagnetic and antiferromagnetic behavior for 1 and 2, respectively. Density functional theory calculations (B3LYP functional) were performed for further insight on the trinuclear units to provide a qualitative theoretical interpretation on the overall magnetic behavior of the complexes 1 and 2. {\textcopyright} 2010 Elsevier B.V. All rights reserved.