Synthesis of a new polymorph in [Cu(pyridine-2-carboxylate)₂] system

1656-1660Single crystal X-ray studies on a doubly carboxylate bridged {[Cu(pic)₂].2H₂O}ո (1) (pic = pyridine-2-carboxylate) polymeric chains extending along the crystallographic a axis reveal that adjacent polymeric chains are joined by the lattice water chains running parallel to the polymeric chain leading to a 2D sheet in the (101) plane. The successive sheets are interdigitated and glued to each other by a novel C=O…π interaction into a 3D supramolecular motif. The complex (1) can be regarded as a pseudo-polymorph of [Cu(pic)₂]ո which has been realized in two forms, violet (2) and blue-violet (3) from methanol

Synthesis and structural characterization of a novel homo-binuclear complex [Cu(dinemac)(H₂O)₂][Cu(dipic)₂] .3H₂O: Assembly of discrete cationic and anionic components in a 1D chain through H bonding

261-264This work describes the synthesis and structural characterization of a novel homo-binuclear coppcr(II) complex [Cu(dinemac)(H2O)2] [Cu(dipic)2].3H2O (1), in which the macrocylic cationic modules are assembled with the anionic components through H bonding. The X-ray siructural analysis indicates that the central atoms Cu(1) and Cu(2) of the two independent cations lic on crystallographic centers of symmetry and that the independent anion with its central atom Cuʹ is sited at a general position. The asymmetric unit of 1 consists of two halves of [Cu(dinemac)(H2O)2]2+ cations, a [Cu(dipic)2]2- anion and three water molecules. The room temperature solid state EPR spectrum of the polycrystalline sample is typical for a non-distorted or exchange averaged mononuclear Cu(II) complex with gav=2.146±0.005 and ΔHpp=9.5 mT

Detection of Curvature-Radius-Dependent Interfacial pH/Polarity for Amphiphilic Self-Assemblies: Positive versus Negative Curvature

It is possible that a defined curvature at the membrane interface controls its pH/polarity to exhibit specific bioactivity. By utilizing an interface-interacting spiro-rhodamine pH probe and the Schiff base polarity probe, we have shown that the pH deviation from the bulk phase to the interface (ΔpH)/interfacial dielectric constant (κ­(i)) for amphiphilic self-assemblies can be regulated by the curvature geometry (positive/negative) and its radius. According to ¹H NMR and fluorescence anisotropy investigations, the probes selectively interact with an anionic interfacial Stern layer. The ΔpH/κ­(i) values for the Stern layer are estimated by UV–vis absorption and fluorescence studies. For the anionic sodium bis-2-ethylhexyl-sulfosuccinate (AOT) inverted micellar (IM) negative interface, the highly restricted water and proton penetration into the Stern layer owing to tight surfactant packing or a reduced water-exposed headgroup area may be responsible for the much lower ΔpH ≈ −0.45 and κ­(i) ≈ 28 in comparison to ∼−2.35 and ∼44, respectively, for the anionic sodium dodecyl sulfate (SDS) micellar positive interface with a close similar Stern layer. With increasing AOT IM water-pool radius (1.7–9.5 nm) or [water]/[AOT] ratio (<i>w</i>₀) (8.0–43.0), the ΔpH and κ­(i) increase maximally up to ∼−1.22 and ∼45, respectively, due to a greater water-exposed headgroup area. However, the unchanged ΔpH ≈ −0.65 and κ­(i) ≈ 53.0 within radii ∼3.5–8.0 nm for the positive interface of a mixed Triton X-100 (TX-100)/SDS (4:1) micelle justify its packing flexibility. Interestingly, the continuously increasing ΔpH trend for IM up to its largest possible water-pool radius of ∼9.5 nm may rationalize the increase in ΔpH (∼−1.4 to −1.6) with the change in the curvature radii (∼15 to 50 nm) for sodium 1,2-dimyristoyl-<i>sn</i>-glycero-3-phosphorylglycerol (DMPG)/1,2-dimyristoyl-<i>sn</i>-glycero-3-phosphocholine (DMPC) (2:1) large unilamellar vesicles (LUV) owing to its negative interface. Whereas, similar to the micellar positive interface, the unchanged ΔpH at the positive LUV interface was confirmed by fluorescence microscopic studies with giant unilamellar vesicles of identical lipids composition. The present study offers a unique and simple method of monitoring the curvature-radius-dependent interfacial pH/polarity for biologically related membranes

Two highly unsymmetrical tetradentate (N3O) Schiff base copper(II) complexes: Template synthesis, structural characterization, magnetic and computational studies

Two new copper(II) complexes, [Cu-2(L-1)(2)](ClO4)(2) (1) and [Cu(L-2)(ClO4)] (2), of the highly unsymmetrical tetradentate (N3O) Schiff base ligands HL1 and HL2 (where HL1 = N-(2-hydroxyacetophenone)-bis-3-aminopropylamine and HL2 = N-(salicyldehydine)-bis-3-aminopropylamine) have been synthesised using a template method. Their single crystal X-ray structures show that in complex 1 two independent copper(II) centers are doubly bridged through sphenoxo-O atoms (O1A and O1B) of the two ligands and each copper atom is five-coordinated with a distorted square pyramidal geometry. The asymmetric unit of complex 2 consists of two crystallographically independe N-(salicylidene) bis(aminopropyl)amine-copper(II) molecules, A and B, with similar square pyramidal geometries. Cryomagnetic susceptibility measurements (5-300 K) on complex 1 reveal a distinct antiferromagnetic interaction with J=-23.6 cm(-1), which is substantiated by a DFT calculation (J=-27.6 cm(-1)) using the B3LYP functional. Complex 1, immobilized over highly ordered hexagonal mesoporous silica, shows moderate catalytic activity for the epoxidation of cyclohexene and styrene in the presence of TBHP as an oxidant

Geometrical isomers of [TEAH][Co(L-Se)(2)]center dot xH(2)O: synthesis, structural, spectroscopic and computational studies

Trans-1, [HNEt3][Co-III(L-Se)(2)]center dot H2O and cis-1, [HNEt3][Co-III(L-Se)(2)]center dot 3H(2)O have been synthesized and characterized by single-crystal X-ray studies. The counter ion Et3NH+ plays a crucial role in the crystal packing leading to the formation of two distinctly different supramolecular assemblies in the two complexes. In trans-1, Co-bisphenolate units and triethylamine molecules are arranged in a linear fashion leading to a supramolecular columnar assembly along the crystallographic a-axis. In this assembly, triethylammonium ions are sandwiched between successive Co-bisphenolate units and act as gluing agents joining Co-bisphenolate units on either side through C-H center dot center dot center dot pi interactions. In sharp contrast to trans-1, Co-bisphenolate units and triethylammonium ions in cis-1 are arranged in a helical supramolecular assembly through similar C-H center dot center dot center dot pi interactions along the crystallographic b-axis. The Se center dot center dot center dot Se van der Waals interactions may be responsible for the predominant occurrence of the cis-isomer. The cyclic voltammetric studies showed quasi-reversible waves for the cobalt(III) -> cobalt(II) reductions with E-1/2 = 0.635 and 0.628 V vs. Ag/AgCl for cis-1 (at similar to 5 degrees C) and trans-1 (at similar to 25 degrees C), respectively. DFT calculations show that the trans-form is the thermodynamic product with higher stability than the cis-one, which is consistent with the variable temperature H-1 NMR studie