Tamal Kanti Ghosh

Bis-Heteroleptic Ruthenium(II) Complex of Pendant Urea Functionalized Pyridyl Triazole and Phenathroline for Recognition, Sensing, and Extraction of Oxyanions

A new bis-heteroleptic RuII complex based ditopic receptor, 1[PF6]2, having an anion binding triazole -CH unit and appended 4-fluorophenyl urea arm has been developed. 1H NMR and isothermal titration calorimetry (ITC) experiments showed binding of 1[PF6]2 toward oxyanions such as phosphates (e.g., H2PO4- and HP2O73-) and carboxylates (e.g., CH3CO2- and C6H5CO2-) anions selectively. 1H NMR studies showed that highly basic phosphate anions such as HP2O73-/H2PO4- are bound by both -CH and -NH units of complex 1[PF6]2. However, comparatively less basic CH3CO2-, C6H5CO2- anions interacted with the urea -NH protons only. Thermodynamic parameters obtained from ITC experiments suggested that binding of all the interacting anions with complex 1[PF6]2 are highly enthalpy and entropy driven processes. Importantly, complex 1[PF6]2 showed extraction of H2PO4-, CH3CO2-, and C6H5CO2- anions from aqueous solution via liquid-liquid extraction with efficiencies of 28%, 74%, and 80%, respectively. The influential role of the urea moiety in the course of extraction is demonstrated by comparison with a model complex, 2[PF6]2. Additionally, complex 1[PF6]2 is capable of selective sensing of phosphate anions among all investigated anions.

Effect of coordinating (–CN) vs. non-coordinating (–F) substituents in 3-pyridyl urea receptors toward second sphere sulfate recognition: selective crystallisation of CuSO4 from mixtures of competing anions/cations

4-Fluorophenyl and 4-cyanophenyl substituted 3-pyridyl urea, L1111 and L2222 respectively, were synthesized and explored extensively to demonstrate SO42− binding via second sphere coordination in their respective self-assembled structures assisted by Cu2+, Cd2+ and Co2+. A single crystal X-ray diffraction study depicts second sphere SO42− recognition in the C4v symmetric cleft formed by the assembly of four molecules of the Cu2+ complex of L1111, [CuL11114(H2O)2]SO4, (1), via eight N–H⋯O interactions from four urea moieties. Similarly, second sphere SO42− recognition via twelve hydrogen bonding interactions (N–H⋯O and C–H⋯O) is also demonstrated in the assembly of the Cd2+ complex of L1111 i.e. [CdL11114(H2O)2]SO4, (2). Detailed structural analysis of 1 and 2 shows the formation of the coordination complexes of Cu2+ and Cd2+ with four units of pyridyl urea, which further assemble to generate a suitable coordination environment for the recognition of SO42− via second sphere coordination. On the other hand, L2222 with a coordinating substituent shows second sphere SO42− coordination with eleven hydrogen bonding interactions (N–H⋯O and C–H⋯O) via the formation of a Cu2+ assisted 1D coordination polymer [{CuL22224}SO4]α, (3). The coordinating property of the –CN of L2222 is reflected in 3, as it directly coordinates to the Cu2+ that assists the formation of the 1D coordination polymer. Second sphere coordination of SO42− in the assembly of L2222 is also established with Co2+ in its complex, [CoL22222(H2O)4]SO4, (4). However, in this case the metal ion prefers to form a coordination complex, as observed in 1 and 2, instead of the 1D-polymeric network in 3. The solution state UV-Vis studies of L1111 with various copper salts, such as Cu(ClO4)2, CuSO4, Cu(NO3)2, CuCl2 and their mixtures show the selective formation of 1. Cu2+ selective second sphere coordination of SO42− in solution is also demonstrated by UV-Vis studies of the complex isolated from the mixtures of various Cu2+ salts or SO42− salts of different metal ions. Furthermore, the selective formation of complex 1 is also demonstrated when complexation of CuSO4 is carried out with mixtures of L1111 and L2222 in MeOH–H2O.

Unusual Recognition and Separation of Hydrated Metal Sulfates [M2(μ-SO4)2(H2O)n, M = ZnII, CdII, CoII, MnII] by a Ditopic Receptor

A ditopic receptor L1, having metal binding bis(2-picolyl) donor and anion binding urea group, is synthesized and explored toward metal sulfate recognition via formation of dinuclear assembly, (L1)2M2(SO4)2. Mass spectrometric analysis, (1)H-DOSY NMR, and crystal structure analysis reveal the existence of a dinuclear assembly of MSO4 with two units of L1. (1)H NMR study reveals significant downfield chemical shift of -NH protons of urea moiety of L1 selectively with metal sulfates (e.g., ZnSO4, CdSO4) due to second-sphere interactions of sulfate with the urea moiety. Variable-temperature (1)H NMR studies suggest the presence of intramolecular hydrogen bonding interaction toward metal sulfate recognition in solution state, whereas intermolecular H-bonding interactions are observed in solid state. In contrast, anions in their tetrabutylammonium salts fail to interact with the urea -NH probably due to poor acidity of the tertiary butyl urea group of L1. Metal sulfate binding selectivity in solution is further supported by isothermal titration calorimetric studies of L1 with different Zn salts in dimethyl sulfoxide (DMSO), where a binding affinity is observed for ZnSO4 (Ka = 1.23 × 10(6)), which is 30- to 50-fold higher than other Zn salts having other counteranions in DMSO. Sulfate salts of Cd(II)/Co(II) also exhibit binding constants in the order of ∼1 × 10(6) as in the case of ZnSO4. Positive role of the urea unit in the selectivity is confirmed by studying a model ligand L2, which is devoid of anion recognition urea unit. Structural characterization of four MSO4 [M = Zn(II), Cd(II), Co(II), Mn(II)] complexes of L1, that is, complex 1, [(L1)2(Zn)2(μ-SO4)2]; complex 2, [(L1)2(H2O)2(Cd)2(μ-SO4)2]; complex 3, [(L1)2(H2O)2(Co)2(μ-SO4)2]; and complex 4, [(L1)2(H2O)2(Mn)2(μ-SO4)2], reveal the formation of sulfate-bridged eight-membered crownlike binuclear complexes, similar to one of the concentration-dependent dimeric forms of MSO4 as observed in solid state. Finally, L1 is found to be highly efficient in removing ZnSO4 from both aqueous and semiaqueous medium as complex 1 in the presence of other competing Zn(II) salts via precipitation through crystallization. Powder X-ray diffraction analysis has also confirmed bulk purity of complex 1 obtained from the above competitive crystallization experiment.

The 2{ital p}{sup 5}3{ital l} configurations of highly stripped Ne-like ions: Possibility of x-ray laser emission

The 2{ital p}{sup 5}3{ital l} ({ital l}=0,1,2) singlet configurations of highly stripped Ne-like ions from Ar{sup 8+} to Kr{sup 26+} have been calculated using time-dependent coupled Hartree-Fock theory, and their transition schemes are analyzed. Many of these lines are observed from laser-produced plasmas of the respective atoms and are useful for high-temperature plasma diagnostics and in stellar opacity projects. The data are very useful for understanding and modeling of laser action at short wavelengths, particularly in the X-ray region. The lasing action usually occurs from transitions with the levels 2{ital p}{sup 5}3{ital p}{r_arrow}2{ital p}{sup 5}3{ital s}. Transition energies, oscillator strengths, and dipolar and quadrupolar transition probabilities have been estimated for all the excitations studied. Results agree well with experimental and theoretical data wherever available. {copyright} {ital 1995 The American Astronomical Society.}

Interconfiguration Forbidden Transitions in Argon Isoelectronic Ions

Transition properties such as transition energies, oscillator strengths, transition probabilities, and quantum defect values have been reported for the interconfiguration forbidden transitions 3p6:1Se → 3p5(2P)np:1De (n = 4, 5, 6, 7) and 3p6:1Se → 3p5(2P)nf:1De (n = 4, 5, 6, 7) for the first few members of Ar isoelectronic sequence from Ar to Cr6+. The linearized version of time-dependent coupled Hartree-Fock (TDCHF) theory has been applied to calculate such transition properties. These data are very useful in identifying the solar spectral lines in the ultraviolet region. Most of the data for oscillator strengths, transition probabilities, and quantum defect values from K+ onward are new. Transition energies agree well with the existing experimental results wherever available.

Doubly excited3Se,3De and3Ge states of two-electron atomic systems

SummaryTime-dependent perturbation theory has been applied to calculate the doubly excited triplet statesNsns:3Se,Npnp:3De andNdnd:3Ge (N=2, 3, 4,n=N+1, ... ,5) for He, Li+, Be2+ and B3+. A time-dependent harmonic perturbation causes simulataneous excitation of both the electrons with a change of spin state. The doubly excited energy levels have been identified as the poles of an appropriately constructed linearized variational functional with respect to the driving frequency. In addition to the transition energies, effective quantum numbers of these doubly excited states have been calculated and analytic representations of their wave functions are obtained. These are utilized to estimate the Coulomb repulsion term for these states which checks the consistency of the wave functions. These wave functions may also be used for calculating other physical properties of the systems.

Chapter 3:Anion Binding in Tripodal Receptors and Supramolecular Capsular Dimeric Assemblies

Comprehensive overview on the development of anion recognition by tripodal receptors and supramolecular capsular dimeric assemblies has been conferred. Discussion is carried out by focusing on the functionalities like, amide, urea, amine and zwitter ion on which various tripodal receptors have been developed. This book chapter illustrates the development of tripodal anion receptors and their capsular dimeric assemblies in anion chemistry where different characterization techniques like; 1H-NMR, ITC, Single crystal X-ray structural studies etc. have been employed to establish anion binding.

On the interpretation of two electron-one photon transitions in slow collisions between fully stripped ions and solid target

The two electron-one photon transitions occuring in slow collisions of fully stripped neon atoms with solid targets have been interpreted in terms of trapping ofL-shell electrons in bare neon atoms from the solid target and subsequent transitions toK-shell. Experimental X-ray spectra and transition probabilities can be interpreted in terms of actual transitions occurring in such cases explicitly by the present theoretical calculations which takes care of correlation and relaxation effects.