Selective formation of a self-assembling homo or hetero cavitand cage via metal coordination based on thermodynamic or kinetic control

The selective formation of a homo or hetero cavitand cage composed of two molecules of tetra(4-pyridyl)-cavitand (1), tetrakis(4-cyanophenyl)-cavitand (2), or tetrakis(4-pyridylethynyl)-cavitand (3), and four molecules of Pd(dppp)(OTf)(2) (4) or Pt(dppp)(OTf)(2) (5) has been studied. A 1:1:4 mixture of 1 with more steric restriction, 2 with less coordination ability, and 4 or 5 specifically self-assembled into a hetero cavitand cage 6 or 7, respectively. In contrast, a 1:1:4 mixture of 2, 3, and 4 in CDCl(3) at room temperature assembled into the most labile homo cyanophenyl cavitand cage 8 and the most stable homo pyridylethynyl cavitand cage 9 in a 1:1 ratio. Upon heating at 50 degrees C, the thermodynamic equilibrium was shifted to a 1:1:1 mixture of 8, 9, and a hetero cavitand cage 10. When 1 equiv of 3 was added to 8 at room temperature, 8, 9, and 10 were formed initially in a 1:1:3 ratio and finally shifted to a 1:1:1 ratio. In the Pt-system, upon addition of 1 equiv of 3 to homo cyanophenyl cavitand cage 11 in CDCl(3) at room temperature, the ratio of hetero to homo cavitand cage (13/12) initially attained was 8.7 and remained above 5.6 at room temperature. Upon heating at 50 degrees C, 13 was finally converted to 11 and 12. Thus, the selectivity for the self-assembly of the homo or hetero cavitand cage is controlled by the balance between kinetic and thermodynamic stabilities of cages based on a combination of factors such as coordination ability and steric demand of the cavitands.     

A new self-assembling capsule via metal coordination

A new octadentate cavitand forms a stable dimeric molecular capsule via metal-coordination, creating a large and elaborate three-dimensional cavity in which large aromatic guests are accommodated to form supramolecular complexes.     

Metal-selective coordination and enhanced fluorescence of a self-assembling ligand scaffold

A fluorescent hydroxyiminonicotinonitile (HINT) coordinating group can be incorporated into self-assembling ligand scaffolds, and shows metal-selective assembly and enhanced fluorescence. The assembly process is dependent on ligand coordination angle, and coordination only occurs for oxophilic first row transition metal ions, with affinity enhanced by the supramolecular assembly process. The ligands are weakly emissive, and show strong enhancement in fluorescence upon Zn²⁺ coordination, whereas Co²⁺ or Fe²⁺ cause complete quenching.     

Networking a hollow cage via guest coordination

A hollow coordination cage with a highly symmetric cavity was successfully self-assembled to form a 2D-network having a less symmetric cavity via networking of disordered guests with a metal connector.     

A self-assembling metallosupramolecular cage based on cavitand-terpyridine subunits

Metal-directed self-assembly of a terpyridyl-functionalized cavitand yields a large hexameric coordination cage.     

Dramatic tuning of carbon dioxide uptake via metal substitution in a coordination polymer with cylindrical pores

A series of four isostructural microporous coordination polymers (MCPs) differing in metal composition is demonstrated to exhibit exceptional uptake of CO2 at low pressures and ambient temperature. These conditions are particularly relevant for capture of flue gas from coal-fired power plants. A magnesium-based material is presented that is the highest surface area magnesium MCP yet reported and displays ultrahigh affinity based on heat of adsorption for CO2. This study demonstrates that physisorptive materials can achieve affinities and capacities competitive with amine sorbents while greatly reducing the energy cost associated with regeneration.     

Selective synthesis of monomeric or dimeric titanatranes via fine tuning in triethanolateamine ligand

Monomeric titanatrane i-PrOTi(OCMe₂CH₂)₃N (1) and dimeric titanatranes [i-PrOTi(OCH₂CH₂)_nN(CH₂CMe₂O)_3−n]₂ (n = 1, 2; n = 2, 3) were synthesized by the reaction of Ti(O-i-Pr)₄ with a series of triethanolateamines such as (OCH₂CH₂)_nN(CH₂CMe₂O)_3−n³⁻ (n = 0, Lig¹; n = 1, Lig²; n = 2, Lig³), which vary by the number of CMe₂ groups adjacent to a OH functionality from 3 (Lig¹H₃) to 2 (Lig²H₃) to 1 (Lig³H₃). The resultant titanatranes 1–3 have been characterized by solution ¹H and ¹³C{¹H} NMR and their solid state structures have been determined by X-ray crystallography. Whereas compound 1 is monomeric in the solid state, compounds 2 and 3 are dimeric, due to the reduction of the steric congestion in the vicinity of the Ti.     

Synthesis and studies on metal coordination with a novel carboxyamide ligand

Novel complexes of Co(II), Ni(II), Cu(II) and Pd(II) with the new ligand [N,N'-bis(2-carboxy-1-oxo-phenelenyl)ethylenediamine] (H2L) have been synthesized and characterized on the basis of elemental analyses, magnetic susceptibility, thermal, infrared, electronic, 1H NMR and EPR spectral studies. Infrared and 1H NMR spectra show that H2L acts as a binegative tetradentate ligand. Coordination occurs through deprotonated carboxylate oxygens and nondeprotonated amido nitrogens in all the complexes. Electronic spectral studies and magnetic moment values suggest N2O2 coordination around each metal centre with strong field square planar chromophores. The probable structures of the complexes have been assigned on the basis of spectral studies. The complex formation between M(II) [M(II) = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)] and (L2-) has also been studied potentiometrically in 75% aqueous DMF at 25 degrees C in 0.1 M NaClO4. The stability constants were found to follow the order: Mn(II) < Co(II) < Ni(II) < Cu(II) > Zn(II).     

Selective formation of a polar incomplete coordination cage induced by remote ligand substituents

Instead of highly symmetrical T-symmetry cages common in self-assembly, the p-NMe(2)-substituted triphosphine CH(3)C{CH(2)P(4-C(6)H(4)NMe(2))(3) gives open, polar C(3) symmetry cages [Ag(6)(triphos)(4)X(3)](3+) which lack one of the expected face-capping anions; despite its subtlety this difference occurs selectively in solution and two examples have been crystallographically characterised.     

Helical and network coordination polymers based on a novel C2-symmetric ligand : SHG enhancement through specific metal coordination

Cu(I) and Ag(I) coordination polymers of an axially chiral "push-pull" ligand possess respectively 2-D network and helical structures and the coordination mode strongly influences the solid state SHG reduction/enhancement with respect to the free ligand.     

A two dimensional coordination polymer based on drug ligand enoxacin and transition metal ion

A two-dimensional coordination polymer, [Mn(Enox)₂]·4H₂O, 1 (H-Enox?=?1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-pierazinyl)-1,8-naphtyridine-3-carboxylic acid), has been rationally designed and synthesized under hydrothermal conditions. Compound 1 is self-assembled from bifunctional drug ligand enoxacin and transition metal ion Mn(II) through covalent coordination bonds and hydrogen bondings.     

Self-assembly and anion-exchange properties of a discrete cage and 3D coordination networks based on cage structures

By using tridentate ligand 4-(3-pyridinyl)-1,2,4-triazole (pytrz), cage-like complexes of {[Cu(mu2-pytrz)2](ClO4)(SO4)0.5C2H5OH.0.25 H2O}6 (1), {[Cu3(mu3-pytrz)4(mu2-Cl)2(H2O)2](ClO4)2Cl(2).2 H2O}n (2), and {[Cu3(mu3-pytrz)3(mu3-O)(H2O)3](ClO4)2.5(BF4)(1.5)5.25 H2O}n (3) have been synthesized with different copper(II) salts. Complex 1 represents the second example of a M6L12 metal-organic octahedron with an overall Th symmetry. Complex 2 is constructed from a 3(8) cage-building unit (CBU) and each CBU connects six neighboring cages to give the first 3D metal-organic framework (MOF) based on octahedral M6L12. Complex 3 is built from Cu24(pytrz)12 CBUs with the trinuclear copper clusters serving as second building units (SBUs) and decorating each corner of the M24L12 polyhedron. The Cu24(pytrz)12 building unit is linked by extra ligands to give an extended 3D framework that has the formula Cu24(pytrz)24 and possesses a CaB6 topology. The mixed anions ClO4- and BF4- in 3 are both included in the inner cavity of the cage and can be completely exchanged by ClO4- through the open windows of the cage, as evidenced by the crystal structure of the 3D MOF {[Cu3(mu3-pytrz)3(mu3-O)(H2O)3](ClO4)(4)4.5 H2O}n (4). Complex 4 can also be synthesized when employing 1 as a precursor in an extensive study of the anion-exchange reaction. This represents the first successful conversion of a discrete cage into a 3D coordination network based on a cage structure. Complex 2 remains invariable during anion-exchange reactions because uncoordinated Cl- ions are located in the comparatively small inner cavity.     

An interlocked coordination cage based on aromatic amide ligands

An interlocked M_4 L_8 coordination cage was synthesized by coordination-driven self-assembly of palladium(Ⅱ) ions with aromatic amide bidentate ligands.The reaction of the ligand and the metal at 2:1 ratio led to the monomeric M_2 L_4 cage as the kinetic product,while the thermodynamic product M_4 L_8 cage was obtained by prolongating the reaction.This conve rsion and the interlocked structure was clearly revealed by using ~1 H NMR,mass spectrometry and X-ray crystallography.The driving force of interlocking was mainly attributed to the interactions(hydrogen bonding,aromatic stacking and electrostatic interaction) arising from the aptitude of flexibility of the amide ligand.     

pH-Controlled selection between one of three guests from a mixture using a coordination cage host

We demonstrate the use of a simple pH swing to control the selection of one of three different guests from aqueous solution by a coordination cage host. Switching between different guests is based on the fact that neutral organic guests bind strongly in the cage due to the hydrophobic effect, but for acidic or basic guests, the charged (protonated or deprotonated) forms are hydrophilic and do not bind. The guests used are adamantane-1,3-dicarboxylic acid (H₂A) which binds at low pH when it is neutral but not when it is deprotonated; 1-amino-adamantane (B) which binds at high pH when it is neutral but not when it is protonated; and cyclononanone (C) whose binding is not pH dependent and is therefore the default guest at neutral pH. Thus an increase in pH can reversibly switch the host between the three different bound states cage·H₂A (at low pH), cage·C (at medium pH), and cage·B (at high pH) in succession.     

Divalent metal phosphonate coordination polymers constructed from a dipiperidine-based bisphosphonate ligand

The ligand 4,4'-dipiperidine-N,N'-bis(methylenephosphonic acid), H(4)L, has been reacted with divalent metal salts under solvothermal conditions to yield seven new metal phosphonate coordination polymers. The compounds have been characterized by elemental analyses and their structures determined by single-crystal X-ray diffraction. Zn(2)(L)(H(2)O)(2) and Co(2)(L)(H(2)O)(2) have (different) layered structures, while Mn(2)(L)(H(2)O)(3) has a chain motif. In these compounds, the N atoms of the ligand bind to the metal ions. α-Co(2)Cl(2)(H(2)L), formed from CoCl(2)·6H(2)O and H(4)L in ethanol, is also layered but the N atoms of the ligand are protonated. The Co atoms are tetrahedral, coordinated by three phosphonate oxygen atoms and a chloride ion. A polymorph of this compound, β-Co(2)Cl(2)(H(2)L), was obtained from a mixed ionic liquid under microwave irradiation. The primary difference between the polymorphs is the orientation of the phosphonate group relative to the dipiperidine. When reacted hydrothermally with Sn(II)C(2)O(4), H(4)L partially decomposes, producing phosphate ions which are incorporated into the structure of Sn(6)O(2)(H(2)L)(PO(4))(2)·4H(2)O. In this compound, the N atoms of the ligand are protonated, and two oxide anions are incorporated for charge balance. A second phase is obtained from the same reaction, which was determined to be Sn(7)O(L)(3). This compound has a layered structure which contains relatively large voids within the inorganic portion of the layer. These structures are discussed, as well as factors influencing the state of protonation in the final compounds. The choice of solvent and temperature were found to have a significant influence on the type of structure obtained.     

Electronic response of a (P,N)-based ligand on metal coordination

The reaction of [(THF)Li(Ph(2)PC(H)Py)] with ZnCl(2) in the presence of ZnO yields the zinc complex [Zn(3)(Ph(2)PC(H)Py)(4)O] (1). Deprotonation of the phosphane Ph(2)P(CH(2)Py) with [Fe(N(SiMe(3))(2))2] gives the iron complexes [(Ph(2)P(CH(2)Py))Fe(Ph(2)PC(H)Py)2] (2) and [Fe(Ph(2)PC(H)Py)(N(SiMe(3))(2))]2 (3), depending on the ratio of phosphane. The solid state structures of the metal complexes illustrate the coordination flexibility of the [Ph(2)C(H)Py](-)-anion. Depending on the electronic requirements of the coordinated metal the anion acts as a (P,N)-chelating amide or C-coordinating carbanion with the P- and N-heteroatoms as donor bases.     

Tunable photochromism of spirooxazines via metal coordination

Through the incorporation of a phenanthroline ligand into the oxazine moiety of photochromic spirooxazines, a series of photochromic spirooxazine-phenanthroline metal complexes have been synthesized, resulting in tunable and significantly increased photoresponsivities. Such systems are of interest for the investigation of multifunctional photochromic materials. These novel metal complexes retain their photochromic activity in the complexed state, leading to ligand binding in both the spirooxazine and the photomerocyanine forms during the photoconversion. A significant stabilization of the photomerocyanine form results from metal complexation, as indicated by the shift in thermal equilibrium values (KT = 0.06) upon metal complexation (KT = 0.6-1.2). Photoconversion occurs with first-order kinetics, suggesting the absence of an intermediate state. A third photostationary state is observed in these systems induced by visible irradiation of the thermal equilibrium state, leading to a three-state system. This new class of compounds provides the opportunity to investigate the synergy between changes in electronic structure associated with photoisomerization, and metal-centered functionality.     

Transition metal coordination complexes based on V-shaped bis-triazole ligand: syntheses,structures, and properties

Hydrothermal reactions of 1,3-bis(1,2,4-triazol-1-yl)benzene (btb) and M(NO₃)₂ (M = Co²⁺ (1), Cu²⁺ (2)) afforded two new coordination polymers, [Co(btb)₂(NO₃)(H₂O)]_n·NO₃·H₂O (1) and [Cu(btb)₂(NO₃)₂]_n (2), respectively. Single-crystal X-ray diffraction reveals that 1 crystallizes in the space group P2₁/m and 2 crystallizes in the space group Pī, both showing a double-stranded chain structure. The 1-D chains are interconnected via π?π interactions to lead to 2-D ladder-like supramolecular architectures. In addition, magnetic behavior and thermal stability of 1 and 2 have been investigated. For 1, weak antiferromagnetic interactions are observed at low temperature, and the data obey the Curie–Weiss law χ_M = C/(T?θ), with C = 3.22 cm³·mol^?1·K and θ = ?10.39 K. For 2, the decrease of the χT vs. T curve at low temperature is the result of intermolecular antiferromagnetic magnetic interactions.