Hydrogen‐Bond‐Based Magnetic Exchange Between μ‐Diethylnicotinamide(aqua)bis(X‐salicylato)copper(II) Polymeric Chains

Polymeric salicylatocopper(II) complexes of unusual composition [C u(X‐ sal)₂( μ‐denia)(H₂O)]_n [denia = diethylnicotinamide, and X‐sal = 5‐methylsalicylate ( 1 ), 3‐methylsalicylate ( 2 ), 4‐methoxysalicylate ( 3 ), 3,5‐dichlorosalicylate ( 4 ) and 3,5‐dibromosalicylate ( 5 )] were synthesized and characterized. Magnetic measurements were performed in the temperature range 1.8–300 K. The structural unit of all complexes consists of a Cu^II atom, which is monodentately coordinated by the pair of X‐salicylate anions in trans positions. Water and the diethylnicotinamide ligand occupy the other two basal plane positions of the tetragonal pyramid. The axial positions are occupied by a diethylnicotinamide oxygen atom of neighboring structural units, thus forming a spiral polymeric structure parallel to b axis. Magnetic measurements showed that all complexes 1 – 5 exhibit a susceptibility maximum at about 6–8 K. The obtained data fit to Bleaney–Bowers equation gave singlet‐triplet energy gaps 2J = –8.60 cm^–1 for 1 , 2J = –6.57 cm^–1 for 2 , 2J = –8.57 cm^–1 for 3 , 2J = –6.82 cm^–1 for 4 , and 2J = –6.45 cm^–1 for 5 . The supramolecular structure based on hydrogen bonds [described by supramolecular synthons R₂²(10) and R₂²(12)] is the pathway for antiferromagnetic interactions of the magnetically coupled pairs of copper atoms of neighboring chains within the 2D supramolecular layers. The results of the magnetic measurements suggest involvement of the COO groups in the magnetic interaction pathway for all five complexes.     

Molecular structures and supramolecular association of chlorodiorganotin(IV) complexes with bis- and tris-dithiocarbamate ligand

Two series of di and trinuclear chlorodiorganotin(IV) complexes derived from bis- and tris-dithiocarbamate ligands have been prepared and structurally characterized. The dinuclear complexes 1-2 of the composition {(R₂SnCl)₂(bis-dtc)} (1, R = Me; 2, R = ⁿBu) have been obtained from R₂SnCl₂ (R = Me, ⁿBu) and the triethylammonium salt of N,N′-dibenzyl-1,2-ethylene-bis(dithiocarbamate). The trinuclear complexes 3-9 with the general formula {(R₂SnCl)₃(tris-dtc)} 3, R = Me, tris-dtc = tris-dtc-Me; 4, R = Me, tris-dtc = tris-dtc-ⁱPr; 5, R = Me, tris-dtc = tris-dtc-Bn; 6, R = ⁿBu, tris-dtc = tris-dtc-Me; 7, R = ⁿBu, tris-dtc = tris-dtc- ⁱPr; 8, R = ⁿBu, tris-dtc = tris-dtc-Bn; 9, R = ^tBu, tris-dtc = tris-dtc-Me) were prepared from R₂SnCl₂ (R = Me, ⁿBu, ^tBu) and the potassium dithiocarbamate salts of (tris[2-(methylamino)ethyl]amine) (tris-dtc-Me), (tris[2-(isopropylamino)ethyl]amine) (=tris-dtc-ⁱPr) and (tris[2-(benzylamino)ethyl]amine) (=tris-dtc-Bn). Compounds 1-9 have been analyzed as far as possible by elemental analysis, FAB⁺ mass spectrometry, IR and NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopy, and single-crystal X-ray diffraction analysis. The solid state and solution studies showed that the dtc ligands are coordinated to the tin atoms in the anisobidentate manner. In all cases the metal centers are five-coordinate. The coordination geometry is intermediate between square-pyramidal and trigonal-bipyramidal coordination polyhedra with τ-values in the range of 0.32-0.53. For the members of each series characterized in the solid state by X-ray diffraction analysis, different molecular conformations were found. The crystal structures show the presence of C-H?Cl, C-H?S, C-H?π, S?Cl, S?S, Cl?Sn and S?Sn contacts.     

Anagostic interactions, revisiting the crystal structure of nickel dithiocarbamate complex and its antibacterial and antifungal studies

The synthesis of Ni(dtc)₂ [dtc = diethyldithiocarbamate] has been achieved by the interaction of NiL(ClO₄)₂ with sodium diethyldithiocarbamate. Although single crystal structure of this complex was already reported (R = 10.6%), we were able to refine crystal structure up to R = 2.99%. We also observed rare C-H?Ni anagostic interactions generally exhibited by d⁸ complexes which were overlooked previously. To investigate the structure of Ni(dtc)₂ in solution, variable temperature NMR spectra in solution have also been recorded between 25 and −50 °C. Ni(dtc)₂ was also tested for antibacterial and antifungal activities. It showed higher activity against the bacteria and fungi than the known antibiotics.     

Immobilization of Xanthine Oxidase on Carbon Nanotubes Through Double Supramolecular Junctions for Biosensor Construction

A novel approach for the noncovalent functionalization of single‐walled carbon nanotubes with enzymes, using a β‐cyclodextrin‐modified pyrene derivative, mono‐6‐ethylenediamino‐(2‐pyrene carboxamido)‐6‐deoxy‐β‐cyclodextrin (Pyr‐βCD), as a molecular bridge for the construction of a supramolecular assembly between the nanotube surface and an adamantane‐modified enzyme, is reported. The Pyr‐βCD derivative was synthesized and its stacking to SWNT through π–π interactions accomplished. The functionalized nanotubes showed low capacity for the nonspecific adsorption of proteins, but were able to immobilize adamantane‐modified xanthine oxidase via host‐guest associations. This double supramolecular junctions‐based approach was employed to modify a glassy carbon electrode with the enzyme/nanotubes complex for designing a biosensor device toward xanthine. The biosensor showed fast electroanalytical response (10 s), high sensitivity (5.9 mA/M cm²) low detection limit (2 µM) and high stability.     

Anion binding and transport by steroid-based receptors

The steroid nucleus is well-established as a scaffold for anion receptors. The bile acids are especially useful, providing inexpensive starting points with helpful substitution patterns. This article describes developments since an earlier review in 2003. Included are podand and cyclic structures, uncharged and positive receptors, and various arrays of H-bond donor and other binding functionality. Applications have been found in anion sensing, selective extractions, transport across bilayer membranes, and the discovery of antibiotics.     

A chitosan-based chemomechanical polymer triggered by stacking effects with aromatic effectors including aminoacid derivatives

Chitosan with a covalently attached anthrylunit is used as chemomechanical polymer, in which stacking and cation-π interactions allow aromatic effector compounds with positively charged nitrogen centers to trigger macroscopic motions in aqueous surrounding. Thus, only protonated heterocycles such as imidazole or histamine lead at pH 5 to expansion, in contrast to toluenesulfonic acid, or pyrazole and pyrimidine. Inorganic salts and pH influence the polymer swelling, and must be taken into account for the calculation of net effects induced by organic effectors. Reversible volume expansions on the top of the swelling effect of water alone are observed as function of different effector structures, showing, for example, 45% net effect with imidazole and 66% with benzimidazole. Aminoacids, for solubility reasons measured in the form of their methylesters, yield smaller expansions, showing, however, a regular and selective increase with the lipophilicity of the residues. The kinetics of effector uptake, which relates to the velocity of expansion, are measured with histamine and follow first order, with t_1/2=2.7 min for 50% absorption.     

Self-Assembly of Supramolecular Architectures Using Chlorotetra(Pyrrole-2-Carboxylato)Diruthenium Molecules as Building Blocks

Two new complexes, based on the unit Ru₂Cl(μ-O₂CC₄H₄N)₄ (1) (O₂CC₄H₄N = pyrrole-2-carboxylate), Ru₂Cl(μ-O₂CC₄H₄N)₄(H₂O)·4H₂O [1(H ₂ O)·4H ₂ O], and Ru₂Cl(μ-O₂CC₄H₄N)₄(Me₂CO) [1(Me ₂ CO)], are synthesized and structurally characterized. The physical properties of these complexes are studied and compared with those previously reported for Ru₂Cl(μ-O₂CC₄H₄N)₄(thf)·thf·H₂O [1(thf)·thf·H ₂ O]. The nature of the solvent molecule bonded to the axial position of the dimetallic unit determines the supramolecular interactions leading to different arrangements in the solid state. The presence of NH groups in the pyrrolic rings favours the existence of hydrogen bond interactions that are present in the three complexes. In addition, complex 1(Me ₂ CO) shows π–π stacking interactions through pyrrolic rings of different dimetallic units. Dedicated to the memory of Prof. F. Albert Cotton.     

Synthesis and Structures of Metallated N‐Heterocyclic Derivatives

The synthesis and structures of five new compounds are reported. [Mg(6‐Oq)₂(phen)₂] ( 1 ), [Na(phen)₃][(6‐HOq)(6‐Oq)] ( 2 ), 1/∞[Cu(3‐Opy)(3‐HOpy)₂(PPh₃)]_∞ ( 3 ), 1/∞[Cu₂{μ‐(6‐Oq)}(PPh₃)₂]_∞ ( 4 ) and [Cu₂(pht)₂(μ‐dppm)₂] ( 5 ) (6‐HOq = 6‐hydroxyquinoline; phen = 1,10‐phenanthroline, 3‐HOpy = 3‐hydroxypyridine; Hpht = phthalimide; dppm = bis‐(diphenylphosphino)methane) were prepared by deprotonation of N‐heterocyclic aromatic compounds with metal alkoxides. 1 – 5 represent useful starting materials for investigating the supramolecular cordination chemistry of organic anhydrides.     

Polymeric bidimensional self-assembling of [Hg(RC6H4NNNC6H4R)2Py] (R = m-acetyl) through metal-η,η-arene π-interactions and non classical C-H?O bonding: Synthesis and X-ray characterization of a bis diaryl symmetric-substituted triazenide complex of Hg(II)

Deprotonated 1,3-bis(3-acetylphenyl)triazene reacts with Hg(CH₃COO)₂ and pyridine to give light-yellow crystals of {[Hg^II(RC₆H₄NNNC₆H₄R)₂Py]}_n (R = acetyl). The tectons [Hg^II(RC₆H₄NNNC₆H₄R)₂Py] [R = CH₃C(O)] are linked to pairs as centrosymmetric dimers through reciprocal metal-η²-arene π-interactions. The dimeric units are operated by a screw axis 2₁ parallel to the crystallographic direction [0 1 0], also through a reflection-translation plane parallel to the c-axis, resulting a supramolecular bidimensional (2D) assembling of the dimeric tectons through non classical C-H?(O)CCH₃ bonding.     

Aesthetics in chemistry

This highlight article invites supramolecular chemists to read the recent paper of Joachim Schummer on the origin of molecular nanotechnology.