Encapsulating ruthenium and osmium with tris(2-aminoethyl)amine based tripodal ligands

The reaction of a series of tripodal ligands, H₃L^1,2 and L^3-6, with [M(PPh₃)₂Cl₂] (M = Ru, Os) affords a family of coordination cage compounds of the type [M^IIIL^1,2] (1-4) or [M^IIL^3-6](BPh₄)₂ (5-12). The Schiff base ligands (H₃L¹, L³, L⁵) have been synthesized by condensation of tris(2-aminoethyl)amine with salicylaldehyde, pyridine-2-aldehyde and 1-methyl-2-imidazolecarboxaldehyde. These ligands were further reduced and subsequently methylated to form the new ligands (H₃L², L⁴, L⁶). Single crystal X-ray diffraction studies of 1 and 2 show that the tripodal ligand wraps around the metal center as a hexadentate ligand to form a cage. All the synthesized compounds have been thoroughly characterized by ESI-MS, FT-IR, UV-Vis and NMR spectroscopic methods. To the best of our knowledge, this is the first ever report of osmium complexes with tris(2-aminoethyl)amine based tripodal ligands. DFT calculations were performed to obtain geometry optimized structures of all the other complexes (3-12).     

Synthesis,Spectroscopic, and Electrochemical Properties of Four Novel Trinuclear RuII Polypyridyl Complexes Containing Diazafluorene

Four tripodal ligands L^1–4 derived from 4,5‐diazafluoren‐9‐one were synthesized. L^1–2 formed by the reaction of 4,5‐diazafluoren‐9‐oxime with 1,3,5‐tris(bromomethyl)benzene, and 1,1,1‐tris(p‐tosyloxymethyl)propane, respectively and L^3–4 formed by the condensation of 9‐(4‐hydroxy)phenylimino‐4,5‐diazafluorene with 1,3,5‐tris(bromomethyl)benzene, and 1,1,1‐tris(p‐tosyloxymethyl)propane, respectively. Four trinuclear complexes [(bpy)₆Ru₃L^1–4](PF₆)₆ ( Ru‐L^1–4 ) were obtained by reaction of Ru(bpy)₂Cl₂ · 2H₂O with ligands L^1–4. The photophysical behaviors of these complexes were investigated by UV/Vis absorption and emission spectrometry. The complexes display metal‐to‐ligand charge transfer absorptions at 441–445 nm and emissions at 571–578 nm. Cyclic voltammetry data of the complexes show one Ru^II‐centered oxidation and three successive ligand‐centered reductions.     

Alkaline‐Earth Metal Cations as Structure Building Blocks for Molecular Cages with Entrapment and Controlled Release of Quintuple Ionic Aggregates

Currently, main‐group metal cations are totally neglected as the structure‐building blocks for the self‐assembly of supramolecular coordination metallocages due to the lack of directional bonding. However, here we show that a common Arrhenius acid–base neutralization allows the alkaline‐earth metal cations to act as charged binders, easily connecting two or more highly directional anionic transition‐metal‐based metalloligands to coordination polymers. With a metal salt such as K⁺PF₆^? added during the neutralization, the main‐group metal‐connected skeleton can be templated by the largest yet reported ionic‐aggregate anion, K₂(PF₆)₃^?, formed from KPF₆ in solution, into molecular metallocages, encapsulating the ion. Crystal‐structure details, DFT‐calculation results, and controlled‐release behavior support the presence of K₂(PF₆)₃^? as a guest in the cage. Upon removal of PF₆^? ions, the cage stays intact. Other ions like BF₄^? can be put back in.     

Selective Host–Guest Interactions of a Transformable Coordination Capsule/Tube with Fullerenes

An M₂L₄ coordination capsule or an M₂L₂ coordination tube was selectively formed by the combination of Hg^II hinges and bent bispyridine ligands. The two structures reversibly interconvert at room temperature in response to modulation of the metal‐to‐ligand ratio and exhibit different host–guest interaction behavior. The capsule alone encapsulates large spherical molecules, fullerenes C₆₀ and C₇₀, and the bound guests are released upon capsule‐to‐tube transformation by the simple addition of metal ions.     

A Supramolecular Sorting Hat: Stereocontrol in Metal–Ligand Self‐Assembly by Complementary Hydrogen Bonding

A combination of self‐complementary hydrogen bonding and metal–ligand interactions allows stereocontrol in the self‐assembly of prochiral ligand scaffolds. A unique, non‐tetrahedral M₄L₆ structure is observed upon multicomponent self‐assembly of 2,7‐diaminofluorenol with 2‐formylpyridine and Fe(ClO₄)₂. The stereochemical outcome of the assembly is controlled by self‐complementary hydrogen bonding between both individual ligands and a suitably sized counterion as template. This hydrogen‐bonding‐mediated stereoselective metal–ligand assembly allows the controlled formation of nonsymmetric discrete cage structures from previously unexploited ligand scaffolds.     

Self‐Assembly of Coordination Polyhedra with Highly Entangled Faces Induced by Metal–Acetylene Interactions

The self‐assembly of nanostructures is dominated by a limited number of strong coordination elements. Herein, we show that metal–acetylene π‐coordination of a tripodal ligand (L) with acetylene spacers gave an M₃L₂ double‐propeller motif (M=Cu^I or Ag^I), which dimerized into an M₆L₄ interlocked cage (M=Cu^I). Higher (M₃L₂)_n oligomers were also selectively obtained: an M₁₂L₈ truncated tetrahedron (M=Cu^I) and an M₁₈L₁₂ truncated trigonal prism (M=Ag^I), both of which contain the same double‐propeller motif. The higher oligomers exhibit multiply entangled facial structures that are classified as a trefoil knot and a Solomon link. The inner cavities of the structures encapsulate counteranions, revealing a potential new strategy towards the synthesis of functional hollow structures that is powered by molecular entanglements.     

Metallosupramolecular Architectures of Ambivergent Bis(Amino Acid) Biphenyldiimides

The metallosupramolecular chemistry of two enantiopure dicarboxylate ligands has been explored for their potential to form discrete or polymeric interlocked motifs. Consequently, both discrete and polymeric supramolecular complexes have been synthesised, yielding M₂L₂ metallomacrocycles ( 1 and 2 ), a heteroleptic M₂L₃ metallomacrobicycle ( 3 ), a non‐interpenetrated coordination polymer ( 4 ), and highly unusual chiral M₈L₈ squares ( 5 and 6 ). There appears to be a preference for the ligands to form M₂L₂‐type metallomacrocyclic structural units (which feature in 1 – 4 ), although these do not engage in any mechanical interlocking, which is perhaps a combined function of the ligand flexibility and relatively small pi‐surface contrasted to previous analogues. Using copper paddlewheel SBUs, chiral double‐walled squares ( 5 and 6 ) are formed with large internal cavities yet poor stabilities, unexpectedly featuring the paddlewheel motifs at the vertices of the polygonal complex.     

Synthesis,Photophysical, and Electrochemical Properties of RuII Polypyridyl Complexes Bridged with two Tetrapodal Symmetric and one Asymmetric Ligands

Two symmetric tetrapodal ligands L^1–2 and one asymmetric tetrapodal ligand L³ based on 4,5‐diazafluoren have been synthesized and characterized. Ligands L^1–2 formed by the condensation of pentaerythrityl tetratosylate with 4,5‐diazafluoren‐9‐oxime and 9‐(4‐hydroxy)phenylimino‐4,5‐diazafluorene, respectively. L³ was prepared by two steps, 9‐(4‐hydroxy)phenylimino‐4,5‐diazafluorene reacted with pentaerythrityl tetratosylate affording 1,1′,1"‐tris[(4,5‐diazafluoren‐9‐ylimino)phenoxymethyl]‐1"′‐(p‐tosyloxymethyl)‐methane, which reacted with 4,5‐diazafluoren‐9‐oxime affording the asymmetric ligand L³. Three tetranuclear Ru^II complexes [(bpy)₈L^1–3Ru₄](PF₆)₈ (bpy = bipyridine) were obtained by the reaction of Ru(bpy)₂Cl₂ · 2H₂O with ligands L^1–3. Spectroscopic studies of these complexes exhibit metal‐to‐ligand charge transfer absorptions at 440–445 nm and emissions at 575–579 nm. The electrochemical behaviors of these complexes are consistent with one Ru^II‐based oxidation couple and three ligand‐centered reduction couples.     

Metal complexes of azo compounds derived from 4-acetamidophenol and substituted aniline

The Ni(II) and Cu(II) complexes of four azo compounds (H₂L^1–4), namely, 2-(p-X-phenylazo)-4-acetamidophenol (X = OCH₃, NO₂, Br, and H for H₂L¹, H₂L², H₂L³, and H₂L⁴, respectively) were prepared and characterized on the basis of their analytical, spectroscopic, magnetic, and conductance data. The isolated complexes are found to have the general formulae [M(HL^1–4)Cl(H₂O)₃] (M = Ni(II) and Cu(II)). The chelates are found to have octahedral structure. The infrared spectra show that H₂L^1–4 ligands are coordinated to the metal ions in a uninegative bidentate manner, with NO donor sites of the azo N and the deprotonated phenolic O. The ligands and their chelates are subjected to thermal analysis. The biological activity of the synthesized ligands and their metal complexes also are screened against the adult Tribolium confusum mortality. They showed remarkable biological activity.     

Influence of structural variation of salamo‐based ligand on supramolecular architectures,Hirshfeld analyses,and fluorescence properties of new tetranuclear NiII complexes

Two new tetranuclear Ni^II complexes, [Ni₄(L¹)₂(N₃)₄(MeOH)₂]·CH₃COCH₃ (1) and [Ni₄(L²)₂(N₃)₄(MeOH)₂]·4CH₃COCH₃ (2) , were synthesized using NiCl₂·6H₂O, NaN₃, and asymmetric salamo‐based ligands H₂L¹ and H₂L², respectively. The structural characterization was made by elemental analyses, infrared (IR) and ultraviolet‐visible (UV‐vis) spectra, and X‐ray diffraction analyses. The results of X‐ray diffraction analyses show that the Ni^II atoms in complexes 1 and 2 are distorted octahedral geometries. Interestingly, the degree of distortion of the ligands in complexes 1 and 2 is different, which indicates that the interaction of Ni^II ions on different ligands is different. Meanwhile, the investigation of molecular packing by employing the Hirshfeld surface analysis exhibits that the percentages of C–H/H–C, O–H/H–O, and H–H/H–H contacts of the complex 1 (or 2 ) are calculated to be 17.7%, 7.9%, and 53.7% (or 18.8%, 13.8%, and 52.5%), respectively, where the H–H/H–H contacts have the characteristics of strong contacts whereas the O–H/H–O hydrogen bonds are considerably weak, and the studies on fluorescence properties further confirm the Ni^II atoms have different binding abilities to the different ligands.     

Metal-directed self-assembly of M3L2 (M=Zn,Cd) metal-organic architectures with a tripodal tris-bidentate chelator

Two discrete M₃L₂ metal-organic architectures, 1 and 2, have been constructed by reaction of a newly designed tripodal tris-bidentate ligand L with M(NO₃)₂ (1: M=Zn; 2: M=Cd). Both complexes together with L have been structurally elucidated by single-crystal X-ray crystallography. Complex 1 exhibits a cationic M₃L₂ coordination architecture bearing three positive charges balanced by three uncoordinated nitrates, while 2 shows a neutral M₃L₂. 1 and 2 both adopt a compressed trigonal prism shape but show no internal cavity due to close ligand-to-ligand interactions. They display totally different intermolecular packing modes in the solid state, which strongly influence the intermolecular π–π interactions. Complex 1 has been arrayed such that each M₃L₂ is surrounded by three neighboring C ₃-symmetry related ones, whereas 2 exhibits a columnar molecular stacking. The distinctive intermolecular packing modes in the solid state between 1 and 2 bring about a small but discernible red shift (4?nm) corresponding to the π–π ^? electronic absorption.     

Tetrahedron

Connecting a triangle base and an apex forms a simplest polyhedron—that is, a tetrahedron. On account of their structural simplicity and stability, two common classes of tetrahedra—namely, M₄L₄ and M₄L₆ (M indicates anions or metal cations, L indicates ligands with C₃ symmetry for M₄L₄ and C₂ symmetry for M₄L₆, respectively)—can be readily constructed from (i) six straight edges through an edge‐bridged strategy or (ii) four triangle faces through a face‐capped strategy, by means of supramolecular or coordination assembly. The intrinsic cavities inside tetrahedra enable them to act as versatile hosts for encapsulating a variety of guests, which leads to a wide range of applications including molecular recognition, catalysis, sensing and so on. In this review, we intend to summarize specifically the work carried out in the realm of porous tetrahedral cages. It includes representative synthetic strategies for the preparation of tetrahedra along with a general summary on their structural features. Thereafter, we will highlight the state‐of‐the‐art progress in various functions of tetrahedra, in addition to presenting a full overview of applications wherein we aim to provide new insights into the design and preparation of new topological geometric structures and functional materials on the basis of the simplest polyhedron—tetrahedron.     

Di‐μ‐acetato‐O:O′‐di‐μ‐acetato‐O,O′:O′‐bis­{[(cyclo­penta­dienyl)tris­(di­methyl­phosphito‐P)­cobalt‐O,O′,O′′]neodymium(III)}

In the title compound, [{η⁵‐CpCo[P(O)(OMe)₂]₃}Nd(O₂CCH₃)₂]₂, with a centrosymmetric mol­ecule, each Nd atom has an eight‐coordination environment, surrounded by a tripodal {L_OMe = CpCo[P(O)(OMe)₂]₃} and four bridging acetato ligands. The coordination geometry around each Nd centre is described as a distorted square‐antiprism and the two different types of acetato ligands have μ‐O:O′‐ and μ‐O,O′:O′‐acetato coordination modes. The Nd—O distances are in the range 2.378 (4)–2.594 (5) Å and the Nd?Nd distance is 3.9913 (6) Å.     

Self-Assembly of Coordination Polyhedra with Highly Entangled Faces Induced by Metal–Acetylene Interactions

The self-assembly of nanostructures is dominated by a limited number of strong coordination elements. Herein, we show that metal–acetylene π-coordination of a tripodal ligand (L) with acetylene spacers gave an M₃L₂ double-propeller motif (M=Cu^I or Ag^I), which dimerized into an M₆L₄ interlocked cage (M=Cu^I). Higher (M₃L₂)_n oligomers were also selectively obtained: an M₁₂L₈ truncated tetrahedron (M=Cu^I) and an M₁₈L₁₂ truncated trigonal prism (M=Ag^I), both of which contain the same double-propeller motif. The higher oligomers exhibit multiply entangled facial structures that are classified as a trefoil knot and a Solomon link. The inner cavities of the structures encapsulate counteranions, revealing a potential new strategy towards the synthesis of functional hollow structures that is powered by molecular entanglements.     

π‐Conjugated [2]Catenanes Based on Oligothiophenes and Phenanthrolines: Efficient Synthesis and Electronic Properties

Novel π‐conjugated topologies based on oligothiophenes and phenanthroline have been assembled by combining their outstanding electronic and structural benefits with the specific properties of the topological structure. Macrocycles and catenanes are prepared by using an optimized protocol of transition metal‐templated macrocyclization followed by efficient Pd‐catalyzed cross‐coupling reaction steps. By using this method, [2]catenanes comprising two interlocked π‐conjugated macrocycles with different ring sizes have been synthesized. The structures of the [2]catenanes and corresponding macrocycles are confirmed by detailed ¹H NMR spectroscopy and high resolution mass spectrometry. Single crystal X‐ray structural analysis of the quaterthiophene–diyne macrocycle affords important insight into the packing features and intermolecular interaction of the new systems. The fully conjugated interlocked [2]catenanes are fully characterized by spectroscopic and electrochemical measurements.     

“Off‐on‐off” Fluorescence pH Switch of Three Trinuclear RuII Complexes Containing Imidazole Rings

Three tripodal ligands H₃L^1–3 containing imidazole rings were synthesized by the reaction of 1,10‐phenanthroline‐5,6‐dione with 1,3,5‐tris[(3‐formylphenoxy)methyl]benzene, 1,3,5‐tris[(3‐formylphenoxy)methyl]‐2,4,6‐trimethylbenzene, and 2,2′,2"‐tris[(3‐formylphenoxy)ethyl]amine, respectively. Trinuclear Ru^II polypyridyl complexes [(bpy)₆Ru₃H₃L^1–3](PF₆)₆ were prepared by the condensation of Ru(bpy)₂Cl₂ · 2H₂O with ligands H₃L^1–3. The pH effects on the UV/Vis absorption and fluorescence spectra of the three complexes were studied, and ground‐ and excited‐state ionization constants of the three complexes were derived. The three complexes act as “off‐on‐off” fluorescence pH switch through protonation and deprotonation of imidazole ring with a maximum on‐off ratio of 5 in buffer solution at room temperature.     

Anion Coordination of Bis‐bisurea Ligands: Aggregation of Dihydrogen Phosphate Anion into Oligomers and Infinite Chains

A series of alkanediyl‐spaced bis‐bisurea ligands ( L² – L⁴ ) were synthesized and their anion coordination behavior studied. These ligands form interesting complexes with polymeric and oligomeric dihydrogen phosphate aggregates in the solid state. The ligands L² and L³ coordinate with H₂PO₄^– anions to form a unique molecular “necklace” with an infinite (H₂PO₄^–)_n chain and surrounding ligand molecules. Meanwhile, two different dihydrogen phosphate‐water oligomers, (H₂PO₄)₆ · (H₂O)₄ and (H₂PO₄)₄ · (H₂O)₂, were observed in the complexes with the ligands L³ and L⁴ . In addition, solution anion binding properties of the ligands were studied by ¹H NMR and UV/Vis spectroscopy.     

两个双核铁（Ⅲ）和三足配体的配合物的合成和晶体结构

运用三足四齿配体三（2－甲基吡啶）胺（TPA）或三（2－甲基苯丙咪唑）胺（TBA）,得到两个双核铁(III)配合物，[Fe₂L₂(μ₂-O)(μ₂-p-NH₂-C₆H₄COO)]³⁺ (L = TPA, 1 和 L = TBA, 2)。两个配合物均为单斜晶系，空间群为P2(1)/c.晶胞参数 1: a = 1.4529(4), b = 1.6622(5), c = 2.0625(6) nm, β= 100.327(5)º, V = 4.900(3) nm³, z = 4, F(000) = 2344, 分子量M_r = 1142.91, Dc = 1.549 g/cm³, R₁ = 0.0544, R₂ = 0.0962. 2: a = 1.3378(4), b = 2.1174(7), c = 2.4351(7) nm, β= 97.315(6)º, V = 6.842(4) nm³, z = 4, F (000) = 3116, 分子量M_r = 1505.08, Dc = 1.444 g/cm³, R₁ = 0.0793, R₂ = 0.1623. 在两个双核铁(III)配合物中，中心的三价铁和配体TPA或TBA上的四个氮原子和两个氧原子通过不同的桥形成一个畸变的八面体构型。     

Analysis of tertiary phosphanes, arsanes, and stibanes as bridging ligands in dinuclear Group 9 complexes

The unusual bridging and semi‐bridging binding mode of tertiary phosphanes, arsanes, and stibanes in dinuclear low‐valent Group 9 complexes have been studied by density functional methods and bonding analyses. The influence of various parameters (bridging and terminal ligands, metal atoms) on the structural preferences and bonding of dinuclear complexes of the general composition [A¹ M¹(μ‐CH₂)₂(μ‐EX₃)M² A²] (M¹, M²=Co, Rh, Ir; A¹, A²=F, Cl, Br, I, κ²‐acac; E=P, As, Sb, X=H, F, CH₃) has been analyzed. A number of factors have been identified that favor bridging or semi‐bridging modes for the phosphane ligands and their homologues. A more symmetrical position of the bridging ligand EX₃ is promoted by more polar E? X bonding, but by less electronegative (softer) terminal anionic ligands. Among the Group 9 metal elements Co, Rh, and Ir, the computations clearly show that the 4d element rhodium exhibits the largest preference for a {M¹(μ‐EX₃)M²} bridge, in agreement with experimental observation. Iridium complexes should be valid targets, whereas cobalt does not seem to support well a symmetric bridging mode. Analyses of the Electron Localization Function (ELF) indicate a competition between a delocalized three‐center bridge bond and direct metal–metal bonding.     

Density functional theory study of calix[4]arene‐N‐azacrown‐5, calix[4]arene‐N‐phenyl‐azacrown‐5, and their complexes with alkali‐metal cations: Na+, K+, and Rb+

Theoretical studies of 1,3‐alternate‐25,27‐bis(1‐methoxyethyl)calix[4]arene‐azacrown‐5 ( L₁ ), 1,3‐alternate‐25,27‐bis(1‐methoxyethyl)calix[4]arene‐N‐phenyl‐azacrown‐5 ( L₂ ), and the corresponding complexes M⁺/ L of L₁ and L₂ with the alkali‐metal cations: Na⁺, K⁺, and Rb⁺ have been performed using density functional theory (DFT) at B3LYP/6‐31G* level. The optimized geometric structures obtained from DFT calculations are used to perform natural bond orbital (NBO) analysis. The two main types of driving force metal–ligand and cation–π interactions are investigated. The results indicate that intermolecular electrostatic interactions are dominant and the electron‐donating oxygen offer lone pair electrons to the contacting RY* (1‐center Rydberg) or LP* (1‐center valence antibond lone pair) orbitals of M⁺ (Na⁺, K⁺, and Rb⁺). What's more, the cation–π interactions between the metal ion and π‐orbitals of the two rotated benzene rings play a minor role. For all the structures, the most pronounced changes in geometric parameters upon interaction are observed in the calix[4]arene molecule. In addition, an extra pendant phenyl group attached to nitrogen can promote metal complexation by 3D encapsulation greatly. In addition, the enthalpies of complexation reaction and hydrated cation exchange reaction had been studied by the calculated thermodynamic data. The calculated results of hydrated cation exchange reaction are in a good agreement with the experimental data for the complexes. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010