Ranjan Dutta

Bis-heteroleptic ruthenium(II) complex of a triazole ligand as a selective probe for phosphates.

A new bis-heteroleptic ruthenium(II) complex (1) of 2-(1-methyl-1H-1,2,3-triazol-4-yl) pyridine (L) ligand was extensively explored for anion sensing studies. 1[PF6]2 shows selective sensing of dihydrogen phosphate (H2PO4(-))/hydrogen pyrophosphate (HP2O7(3-)) among halides, HCO3(-), AcO(-), NO3(-), ClO4(-), HSO4(-), OH(-), BzO(-), H2PO4(-), and HP2O7(3-) in acetonitrile. Enhancement of emission intensity of 1[PF6]2 along with a 10 nm red shift of the emission maximum is observed in the presence of H2PO4(-)/HP2O7(3-) selectively. The photoluminescence (PL) titration experiment of 1[PF6]2 results in binding constants (K(a)) of 5.28 × 10(4) M(-1) and 4.67 × 10(4) M(-1) for H2PO4(-) and HP2O7(3-), respectively, which is in good agreement with the Ka values obtained from UV-vis titration experiments (2.97 × 10(4) M(-1) and 2.45 × 10(4) M(-1) for H2PO4(-) and HP2O7(3-), respectively). High selectivity of 1[PF6]2 toward these two anions in acetonitrile is further confirmed by PL intensity measurement of 1[PF6]2 upon addition of these two anions in the presence of a large excess of other competitive anions. Further, considerable changes in the lifetime (τ) as well as in the decay pattern of 1[PF6]2 in the presence of H2PO4(-)/HP2O7(3-) among all tested anions support the selective binding property of 1[PF6]2 toward these two anions. Significant downfield shift of the triazole -CH proton of 1[PF6]2 with 1 equiv of H2PO4(-) (Δδ = 0.26 ppm) and HP2O7(3-) (Δδ = 0.23 ppm) in deuterated dimethyl sulfoxide proclaim binding mechanism via C-H···anion interaction in solution state. Finally, single-crystal X-ray structural analysis confirms the first example of dihydrogen pyrophosphate (H2P2O7(2-)) recognition via solitary C-H···anion interactions.

Role of wingtip substituents on benzene-platform-based tetrapodal ligands toward the formation of a self-assembled silver carbene cage

Tetrapodal imidazolium ligands L(1)-L(3) as their PF6(-) salts are synthesized in good yields by reacting 1,2,4,5-tetrakis(bromomethyl)benzene with N-methylimidazole, N-benzylimidazole, and N-ethylimidazole, respectively. Single-crystal X-ray diffraction studies of L(1)·4PF6, L(2)·4PF6, and L(3)·4PF6 show the chair conformation of the tetrapodal imidazoliums (L(1)-L(3)), where 1,5- and 2,4-imidazolium moieties are oriented in opposite directions of the benzene plane. The PF6(-) salts of L(1)-L(3) are reacted with Ag2O to synthesize different silver complexes of N-heterocyclic carbene (NHC), 1-3, respectively, in good yields. Crystals of all three complexes suitable for single-crystal X-ray diffraction study are also isolated. Structural analysis of 1, i.e., the complex of L(1)·4PF6 containing methyl as a wingtip substituent, and Ag2O shows the formation of a bimetallic silver NHC (NHC-Ag) complex, [(L(1)-4H)·2Ag]·2PF6, which is rotationally disordered over an inversion of symmetry of the space group P2(1)/c. Elemental analysis and solution-state (1)H and (13)C NMR studies confirm the above molecular formula of complex 1. When L(2)·4PF6 functionalized with the benzyl wingtip moiety is explored for similar complexation with Ag2O, the isolated complex 2 shows the formation of a simple NHC-Ag complex with molecular formula [(L(2)-4H)·2Ag]·2PF6, as observed in the case of 1. Interestingly, the reaction of L(3)·4PF6 containing ethyl as the wingtip substituent and Ag2O shows the formation of a silver-ion-assisted tetranuclear molecular box of [Ag4(L(3)-4H)2](4+) (3).

A Cyanuric Acid Platform Based Tripodal Bis-heteroleptic Ru(II) Complex of Click Generated Ligand for Selective Sensing of Phosphates via C–H···Anion Interaction

A new bis-heteroleptic trinuclear Ru(II) complex (1[PF6]6) has been synthesized from electron deficient cyanuric acid platform based copper-catalyzed azide-alkyne cycloaddition, i.e., CuAAC click generated ligand, 1,3,5-tris [(2-aminoethyl-1H-1,2,3-triazol-4-yl)-pyridine]-1,3,5-triazinane-2,4,6-trione (L1). Complex 1[PF6]6 displays weak luminescence (ϕf = 0.002) at room temperature with a short lifetime of ∼5 ns in acetonitrile. It shows selective sensing of hydrogen pyrophosphate (HP2O7(3-)) through 20-fold enhanced emission intensity (ϕf = 0.039) with a 15 nm red shift in emission maxima even in the presence of a large excess of various competitive anions like F(-), Cl(-), AcO(-), BzO(-), NO3(-), HCO3(-), HSO4(-), HO(-), and H2PO4(-) in acetonitrile. Selective change in the decay profile as well as in the lifetime of 1[PF6]6 in the presence of HP2O7(3-) (108 ns) further supports its selectivity toward HP2O7(3-). UV-vis and photoluminescence titration profiles and corresponding Jobs plot analyses suggest 1:3 host-guest stoichiometric binding between 1[PF6]6 and HP2O7(3-). High emission enhancement of 1[PF6]6 in the presence of HP2O7(3-) has resulted in the detection limit of the anion being as low as 0.02 μM. However, 1[PF6]6 shows selectivity toward higher analogues of phosphates (e.g., ATP, ADP, and AMP) over HP2O7(3-)/H2PO4(-) in 10% Tris HCl buffer (10 mM)/acetonitrile medium. Downfield shifting of the triazole C-H in a (1)H NMR titration study confirms that the binding of HP2O7(3-)/H2PO4(-) is occurring via C-H···anion interaction. The single crystal X-ray structure of complex 1 having NO3(-) counteranion, 1[NO3]6 shows binding of NO3(-) with complex 1 via C-H···NO3(-) interactions.

Arene platform based hexa-amide receptors for anion recognition: single crystal X-ray structural and thermodynamic studies

Five newly synthesized hexa-amide receptors (L1–L5) and previously reported three such receptors (L6–L8) have been explored to investigate binding propensity of anions of various shapes and sizes. Single crystal X-ray structures of five new anion complexes of receptors (L1–L5), complexes (1–5) and previously reported seven such complexes of (L6–L8), complexes (6–12) fall under four categories of conformations such as aaabbb (A), ababab (B), aabaab (C) and aaaaaa (D) depending upon basicity of the anions as well as substituents on the receptor backbones. Moderately basic guest; chloride exhibits two different conformers with A and B patterns with L1 (R = –oNO2C6H4, complex 1) and L4 (R = –pFC6H4, complex 2) respectively in 1 : 2 (host : guest) stoichiometry. On the other hand, strongly basic acetate complexes of L2 (R = –pNO2C6H4), L3 (R = –mCF3C6H4), L5 (R = 4-pyridyl), L6 (R = –C6F5), L7 (R = –mNO2C6H4) and L8 (R –oCF3C6H4) i.e. complexes 3–8 respectively, exhibit a chair like conformer (A) with 1 : 2 (host : guest) stoichiometry. Our previous studies showed recognition of nitrate–water cluster (9) by L6 and nitrate (10) by L8 with (B) and (C) conformations respectively and an unusual conformation (D) was isolated in cases of L7 and L8 with hydrated fluoride clusters [(F)4(H2O)10]4− (11) and [(F)4(H2O)6]4− (12) respectively. Solution state ITC and NMR studies have also shown 1 : 2 stoichiometry of host : guest binding of acetate and fluoride with L1–L8.

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.

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.

Neutral tripodal receptors towards efficient trapping of oxalate

AbstractTris(2-aminoethyl)amine (TREN) based pentafluorophenyl urea and 4-cyanophenyl thiourea receptors have shown encapsulation of oxalate (C2O42−)

Recent developments in anion induced capsular self-assemblies.

\mathrm {C}_{{2}}\mathrm {O}_{{4}}^{{2-}})

Combined solution-phase, solid-phase and phase-interface anion binding and extraction studies by a simple tripodal thiourea receptor

in semi-aqueous environment. A single crystal X-ray study shows trapping of planar conformer of C2O42−

Halogen bonding assisted selective removal of bromide.

\mathrm {C}_{{2}}\mathrm {O}_{{4}}^{{2-}}