Intramolecular MLOH/π and MLNH/π interactions in crystal structures of metal complexes

Intramolecular metal-ligand OH/π (MLOH/π) and metal-ligand NH/π (MLNH/π) interactions in transition metal complexes between aqua or ammine ligand and ligand containing a C6-aromatic ring were investigated in crystal structures deposited in the Cambridge Structural Database (CSD). These intramolecular interactions appear in 38 structures with aqua ligand as the hydrogen atom donor and in 10 structures with ammine ligand as the hydrogen atom donor. Among all these complexes only one is negatively charged, 14 are positively charged and 33 are neutral indicating that the overall charge of the molecule has an influence on the XH/π (X = O or N) interactions. Energy estimated by DFT calculations is approximately 19 kJ mol⁻¹ for the MLOH/π interactions and approximately 15 kJ mol⁻¹ for the MLNH/π interactions. Dedicated to Professor Milan Melník on the occasion of his 70th birthday     

4 + 4] photodimerization of azaanthracenes in both solution and solid phase controlled by cation-π interactions

Regio- and stereoselective [4 + 4] photodimerization reactions of 1- and 2-azaanthracenes were performed in both methanol solution and solid phases to give anti-HT dimers in high yields. In these reactions, intermolecular cation-π interactions between the pyridinium cation and the benzene ring play a key role in preorientation prior to the photodimerization reactions.     

Two significantly different conformations in crystal: formation of a molecular dimer governed by cation-π interactions

Two significantly different conformations were observed in crystal of 1, which form an unsymmetrical molecular dimer governed by cation-π interactions between a pyridinium cation and a phenyl ring, whereas compound 2 forms a head-to-tail type of dimer.     

Syntheses and Br…π supramolecular interactions in the crystal structure of ipriflavone bromides

Supramolecular forces, including electrostatic in- teraction, hydrogen bond, hydrophobic interaction and aromatic stacking interaction, are the important re- search area in supramolecular chemistry and crystal engineering[1]. Aromatic stacking interaction…     

Syntheses and Br...π supramolecular interactions in the crystal structure of ipriflavone bromides

Two novel compounds, 3,8-dibromo-2-methoxyl-7-isopropoxyisoflavanone (1) and 3,6-dibromo-2-methoxyl-7-isopropoxyisoflavanone (2), are synthesized via bromination reaction of their precursor ipriflavone in methanol. The mixture of 1 and 2 co-crystallizes in ethanol and forms two different crystal shapes, the shape of 1 being block and 2 prism, they can be separated manually. 1 and 2 are characterized by IR, ¹H NMR and single crystal X-ray diffraction. The mechanism of bromination reaction is also discussed. 1 crystallizes in the monoclinic space group P2¹/n with cell parameters a = 1.3569(3) nm, b = 0.6706(2) nm, c = 2.0704(4) nm, β = 97.50(2)°, V = 1.8678(6) nm³, Z = 4, Dc = 1.672 Mg/m³, R = 0.0455, wR = 0.0779, F(000) = 936. 2 crystallizes in the monoclinic space group P 2₁/c with cell parameters a =1.3854(17) nm, b = 1.1215(14) nm, c = 1.3038(17) nm, β = 103.71(2)°, V = 1.968(4) nm³, Z = 4, Dc = 1.587 Mg/m³, R = 0.0306, wR = 0.0619, F(000) = 936. The Br...π interactions, hydrogen bonds, aromatic hydrogen bonds and aromatic stacking interactions exist in the crystal structures of 1 and 2, which lead them into supramolecular compounds with a three-dimensional network structure, respectively. 1 and 2 are the isoflavanone derivatives halogenated at C3 and this kind of isoflavanone halides has not been reported yet.     

Host-guest assembly of pyridinium-conjugated calix[4]arene via cation-π interaction

25-(4-Pyridiniumbutoxy)-26,27,28-trihydroxycalix[4]arene bromide 1 was designed to have both host and guest units in one molecule, and was assembled to become an oligomer via a cation-π interaction. X-ray diffraction (XRD) crystallographic study of 1 revealed that it oriented in a one-dimensional structure. Titrimetric ¹H NMR analysis and electrospray ionization mass spectrometry (ESI-MS) analysis indicated that 1 formed an oligomer in solution, and the restraint of the segmental motion would lead to the stabilization of the cation-π interaction compared with a bi-molecular complex composed of 25,26,27,28-tetrahydroxycalix[4]arene and N-butylpyridinium bromide.     

2D and 3D supramolecular assemblies of double cyclopalladated azobenzenes realized by C-H?Cl-Pd, π?π and C-H?π interactions

The double cyclopalladated complex with azobenzene, μ-[(E)-1,2-diphenyldiazene-C^2,8, N^1,2]-di-[chloro(dimethylsulfoxide)palladium(II)]; (DMSO)PdCl(μ-C₆H₄NNC₆H₄)(DMSO)PdCl (1) and its analogous complex with DMF as ancillary ligand, (DMF)PdCl(μ-C₆H₄NNC₆H₄)(DMF)PdCl; μ-[(E)-1,2-diphenyldiazene-C^2,8,N^1,2]-di-[chloro(dimethylformamide)palladium(II)] (2a) were synthesized and the function of cyclopalladated moiety in molecular assembling in the solid state is illustrated by their crystal packings. The polymorphism of 2a and 2b is discussed. The crystal structures reveal assemblies with molecular components self-organized by C-H?Cl-Pd hydrogen bonds, π?π, and C-H?π interactions. The double cyclopalladated complexes of azobenzene, with two Pd-Cl moieties participating in the hydrogen bond formation and π-conjugated system involved in the π?π or C-H?π interactions, represent a new class of building blocks for construction of solid state supramolecular assemblies.     

Encapsulation of metal cations by the PhePhe ligand: a cation-π ion cage

Structures and binding thermochemistry are investigated for protonated PhePhe and for complexes of PhePhe with the alkaline-earth ions Ba(2+) and Ca(2+), the alkali-metal ions Li(+), Na(+), K(+), and Cs(+), and the transition-metal ion Ag(+). The two neighboring aromatic side chains open the possibility of a novel encapsulation motif of the metal ion in a double cation-π configuration, which is found to be realized for the alkaline-earth complexes and, in a variant form, for the Ag(+) complex. Experimentally, complexes are formed by electrospray ionization, trapped in an FT-ICR mass spectrometer, and characterized by infrared multiple photon dissociation (IRMPD) spectroscopy using the free electron laser FELIX. Interpretation is assisted by thermochemical and IR spectral calculations using density functional theory (DFT). The IRMPD spectrum of protonated PhePhe is reproduced with good fidelity by the calculated spectrum of the most stable conformation, although the additional presence of the secondmost stable conformation is not excluded. All metal-ion complexes have charge-solvated binding modes, with zwitterion (salt bridge) forms being much less stable. The amide oxygen always coordinates to the metal ion, as well as at least one phenyl ring (cation-π interaction). At least one additional chelation site is always occupied, which may be either the amino nitrogen or the carboxy carbonyl oxygen. The alkaline-earth complexes prefer a highly compact caged structure with both phenyl rings providing cation-π stabilization in a "sandwich" configuration (OORR chelation). The alkali-metal complexes prefer open-cage structures with only one cation-π interaction, except perhaps Cs(+). The Ag(+) complex shows a unique preference for the closed-cage amino-bound NORR structure. Ligand-driven perturbations of normal-mode frequencies are generally found to correlate linearly with metal-ion binding energy.     

Selective adsorption of potassium and rubidium by metal–organic frameworks supported supramolecular materials

Journal of Radioanalytical and Nuclear Chemistry - A new MOFs-based adsorbent UiO-66@iPCC5 was prepared by hybridization of 25,27-bis(iso-propoxyl)-calix[4]arene-26,28-crown-5 (iPCC5) into the...     

Copper(I) coordination polymers of N,N'-bis[3-(methylthio)propyl]pyromellitic diimide: crystal transformation and solvatochromism by halogen-π interactions

Four copper(I) coordination polymers with ligand N,N'-bis[3-(methylthio)propyl]pyromellitic diimide (L), [Cu(2)I(2)L(2)](n) (1), [Cu(2)I(2)L(2)](n) (2), [Cu(2)I(2)L](n) (3), and {[Cu(2)I(2)L(2)]·CH(2)Cl(2)}(n) (4), have been successfully synthesized and structurally characterized by single-crystal X-ray diffraction. Structural transformations between the polymers were controlled by the appropriate solvent composition, mole ratio, or temperature. When a 1:1 CuI/L ratio was employed, dimorphic products, 1 and 2, based on a rhomboid Cu(2)I(2) cluster were obtained from an acetonitrile solution and from a dichloromethane/acetonitrile solution with ultrasonication, respectively. When a 1:2 CuI/L ratio was employed, polymer 3 based on infinite stair-step polymer (CuI)(∞) was crystallized. Crystalline product 4 was obtained by the transformation of 1 in a mixed-solvent system with a 1:5 acetonitrile/dichloromethane ratio. Polymers 1-4 were transformed into polymer 3 at 197 °C. X-ray structures of 2-4 show short distances (3.406-3.667 ?) between halogens (I(-) and Cl) and aromatic rings. 1 and 4 show solvatochromism; upon inclusion of the colorless electron donor CH(2)Cl(2), the red color changes as a result of the formation of a chloride-π charge-transfer complex 4 of a pale-colored electron acceptor, 1. Therefore, the origin of the red color from 2 and 3 is also assigned as iodide-to-electron-deficient aromatic π charge transfer.     

Synthesis, crystal structures, and supramolecular assemblies of pyrrole-based anion receptors bearing modified pyrrole β-substituents

Dipyrrolyldiketone BF(2) complexes acting as acyclic anion receptors form supramolecular assemblies with structures and properties that are dependent on the pyrrole β-substituents. In particular, although β-alkyl substituents interfered with the formation of stable gel states, the introduction of fluorine moieties induced a stable supramolecular gel when compared to that of β-unsubstituted receptor.     

The C-Cl···π interactions inside supramolecular nanotubes of hexaethynylhexamethoxy[6]pericyclyne

Model complexes of hexaethynylhexamethoxy[6]pericyclyne (HM6P) molecules, with or without dichloromethane (DCM) guests, have been calculated at the M05-2X/6-311G(d,p) DFT level. Analysis of nonbonding interactions shows that the cohesion of the supramolecular tubular assemblies previously observed in the crystal state, relies mainly on C-H···O hydrogen bonds between axial ethynyl and equatorial methoxy substituents of stacked HM6P C(18) macrocycles in a cyclohexane-like chair conformation. The intrinsic binding energy of one HM6P molecule with two neighbors is calculated to be more than 40 kcal mol(-1). The inner channel of the stacks (of ca. 8 ? diameter) are suitable for hosting DCM molecules. Using the Atoms In Molecules (AIM) theory, the interaction between DCM molecules and surrounding triple bonds is analyzed in terms of σ-hole-directed C-Cl···π halogen bonds. A σ-hole-directed Cl···Cl interaction between two chlorine atoms of different DCM molecules is also evidenced.     

An investigation of the positional isomeric effect of terpyridine derivatives: Self-assembly of novel cadmium coordination architectures driven by N-donor covalence and π⋯π non-covalent interactions

Four cadmium compounds based on two pyridyl substituted terpyridine isomers, namely {[Cd₃(L1)₂(SCN)₆](THF)₂}_n (1), [Cd₂(L1)(CH₃OH)Cl₄]_n (2), [Cd₂(L2)₂(N₃)₄] (3) and [Cd₂(L2)₂(SCN)₄] (4) (L1 = 4′-(3-pyridyl)-2,2′:6′,2″-terpyridine, L2 = 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine) have been synthesized and characterized by IR, elemental analyses, and luminescent spectroscopy with the purpose of investigating the influence of isomeric effect on network assembly. In compounds 1 and 2, L1 as a mono-tridentate bridging ligand links Cd^II atoms into 1D grid-like and 2D wave-like polymers. In contrast, in compounds 3 and 4, L2 as a chelating ligand forms Cd^II dimeric structures. The different coordination behaviors and the positional isomer effect were discussed under the same reaction conditions. In addition, three kind of π?π interactions in the four compounds were summarized, two of which could not be observed on tpy-based complexes.     

Synthesis and Complexation Properties of Novel Biscalixarene Composed of Calix[4]arene and Thiacalix[4]arene Subunits

Biscalixarenes, as examples of higher order molecular architectures than normal calixarene derivatives, were studied extensively in the recent years due to they possess two calixarene cavities which have the potential for complexing with two guests in two…     

Multiresponsive supramolecular gels constructed by orthogonal metal–ligand coordination and hydrogen bonding

Macromonomers bearing tridentate 2,6-bis(1,2,3-trizol-4-yl)pyridine (BTP) ligand unit synthesized via CuAAC “click” chemistry in the middle of the chain and two ureidopyrimidinone (UPy) motifs on the ends linked to the central BTP unit via PEGs of various lengths were synthesized and used for the study of gelation both with and without the presence of Eu(III) ions. Various interesting gelation behaviors were found. Gels exhibited various multi-responsive properties, including photoluminescence, mechanoresponsive properties, self-healing abilities, thermorepsonsive properties and chemoresponsive properties. The different gelation abilities and multi-responsive properties for different systems were shown to be resulted from difference in PEG linker lengths and the introduction of orthogonal metal–ligand coordination and hydrogen bonding interactions. The selective responsiveness to different chemicals would allow the development of modular sensory systems that utilize a combination of orthogonal supramolecular interactions.     

Controlled formation of novel supramolecular microbelts or microprisms from aniline and H2PdCl4 driven by coordination and π–π interactions

In this communication, I report the formation of novel supramolecular one-dimensional (1D) structures including microbelts and microprisms by a direct mix of aniline and H₂PdCl₄ aqueous solutions at room temperature. As-formed supramolecular structures were characterised by scanning electron microscopy, X-ray photoelectron spectra and X-ray diffraction techniques. Both coordination and π–π interactions are expected to be responsible for these 1D microstructures. It suggests that the molar ratio of the reactants is crucial to the formation of such 1D structures.     

Syntheses, crystal structures, and magnetic properties of four one-dimensional metal–nitroxide coordination polymers linked by flexible dicarboxylate anions

Four new one-dimensional coordination polymers [Co(IM4Py)₂(adi)(H₂O)₂] _n , [Zn(IM4Py)₂(adi)(H₂O)₂] _n , [Cd(IM4Py)₂(adi)(H₂O)₂] _n , and [Ni(IM4Py)₂(glu)(H₂O)₂] _n (IM4Py = 2-(4′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl, adi = adipate anion and glu = glutarate anion) were synthesized and structurally characterized. The single-crystal X-ray analyses indicate that all four complexes crystallize in neutral one-dimensional chains in which the nitroxide–metal–nitroxide units are bridged by the flexible dicarboxylate anions. The adipate anions adopt the anti/gauche/anti and anti/anti/anti conformations in the Co(II), Zn(II), and Cd(II) complexes, while the glutarate anions only possess the anti/anti conformation in the Ni(II) complex. The magnetic properties of the Co(II) and Ni(II) complexes show the occurrence of weak antiferromagnetic interactions between the metal atoms and the nitroxide radicals.     

Evidence for cation-π interactions in calixcrown·KPic complexes from X-ray crystal structure analysis and energy calculations

Abstract

The crystal and molecular structures of the 1,3-diisopropoxy-p-tertbutyl calix[4]arene crown-5 fixed in the partial cone conformation and that of its potassium picrate salt have been determined by single crystal X-ray diffraction studies. Energy calculations have been performed to gain more insight on the stabilizing cation…ligand interactions. The calculation of the total potential energy indicates that the contribution which comes from the electrostatic polarization induced by the electric field of the cation on the rotated nucleus gives a net stabilizing contribution of almost 6 kcal/mol. A comparison between the molecular geometry of some partial cone 1,3-disubstituted-p-tertbutylcalix[4]arene derivatives is reported and discussed in view of the preorganization principle.     

Structural variability of Ag(I) metal–organic networks: C–H⋯π and metal⋯π interactions

The synthesis and X-ray structural characterization of two silver(I) coordination polymers, [Ag₂(bpp)₂(Phdac)]·5H₂O (1) and [Ag₂(bpp)(HSSal)] (2), are reported, where bpp = 4,4′-trimethylene dipyridine, H₂Phdac = 1,4-phenylenediacetic acid, and H₃SSal = 5-sulfosalicylic acid. X-ray crystallography reveals that the structures are stabilized through hydrogen bonding interactions. The C–H?π and metal?π interactions of aromatic molecules play a crucial role in building a layered framework. Intricate combinations of the weak non-covalent interactions have been analyzed to explore cooperativity and competitiveness in the solid-state structures.