Anions as templates in coordination and supramolecular chemistry

This review aims to highlight the most important recent advances in the area of anion-templated syntheses in supramolecular and coordination chemistry. We published a comprehensive review on this area in 2003 and hence examples prior to this date will only be discussed when essential for clarity of presentation. The current review has been divided into three main sections: (a) anion-templated synthesis of systems with well-defined molecular weights; this includes macrocycles and cages, interlocked species (such as catenanes and rotaxanes), helical assemblies and other selected examples. (b) Anions as templates in polymeric systems; this includes metal-organic frameworks, molecularly imprinted polymers and other selected examples, such as liquid crystalline materials. (c) Anion templates in dynamic combinatorial libraries.     

Stepwise assembly of unsymmetrical supramolecular arrays containing porphyrins and coordination compounds

The stepwise coordination of meso-4'-pyridyl/phenyl porphyrins (4'-PyPs) to different metal centers proved to be an efficient synthetic approach leading to unsymmetrical arrays containing porphyrins and coordination compounds. The first step of this process, treatment of 4'-PyPs with a less than stoichiometric amount of cis,fac-RuCl2(Me2-SO)3(CO) (1), leads to the selective coordination of [cis,cis,cis-RuCl2(Me2SO)2(CO)] fragments ([Ru]) to some of the peripheral 4'-N sites of the 4'-PyPs. Column separation afforded four partially ruthenated 4'-PyPs in pure form: 4'-cis-DPyP[Ru] (2), 4'-trans-DPyP[Ru] (3), (4'-TPyP)[Ru] (4), and (4'-TPyP)[Ru]3 (5). These compounds, which have residual unbound peripheral 4'-N(py) sites (either one or three), were allowed to react with other metal centers that may belong either to a metalloporphyrin or to a coordination compound. When building blocks 2-5 were treated with [Ru(TPP)(CO)(EtOH)] (TPP = meso-tetraphenylporphyrin) in chloroform at room temperature, axial coordination of Ru(TPP)(CO) units ((Ru)) to the available 4'-N(py) sites readily occurred, generating the following arrays containing both perpendicular porphyrins and coordination compounds: (Ru)-(mu-4'-cis-DPyP)[Ru], (Ru)(mu-4'-trans-DPyP)[Ru], (Ru)3(mu-4'-TPyP)[Ru], and (Ru)(mu-4'-TPyP)[Ru]3. Furthermore, building blocks 2, 3, and 5 were treated with a series of coordination compounds capable of binding two pyridylporphyrins either cis to each other (trans-RuCl2(Me2SO)4 and trans,cis,cis-RuCl2(Me2SO)2(CO)2) or trans to each other (trans-PdCl2(C6H5CN)2). Homo- (Ru) and heterobimetallic (Ru-Pd) arrays with as many as seven metal atoms (six Ru and one Pd) and two 4'-PyPs were obtained as follows: trans,cis,cis-RuCl2(Me2SO)2(4'-cis-DPyP[Ru])2, trans,cis,cis-RuCl2(Me2SO)2(4'-trans-DPyP[Ru])2, trans,cis,cis-RuCl2(CO)2(4'-cis-DPyP[Ru])2, and trans-PdCl2(4'-TPyP[Ru]3)2. All the products were thoroughly characterized by 1H NMR spectroscopy. Since the [Ru] fragment is chiral, diastereomers are formed when two or more [Ru] units are bound to a porphyrin. We found that when two 4'-cis-DPyP[Ru] (2) units are coordinated cis to each other on the same metal center, the mutual anisotropic effect of the cis porphyrins differentiates the sulfoxide methyl resonances for the two forms. These and other results indicate that the pyridyl units react independently of the presence or absence of a substituent on the other py rings. Thus, the synthetic strategy should be a general method for linking diverse metal centers through pyridylporphyrins.     

'Liquid litmus': chemosensory pH-responsive photonic ionic liquids

We report on the founding member of a unique class of luminescent ionic liquids integrating a photoacidic anion that responds to the presence of both condensed- and gas-phase basicity; the analytical response is ratiometric in nature, visible to the naked eye, and offers fascinating prospects in smart photofluids, liquid logic gates, electronic noses, and sensory inks.     

Metal thiophosphonates and related compounds: an emerging area of supramolecular coordination chemistry

Nine new compounds containing PS ligands of the types [P(OtBu)S3]2-, [ArP(StBu)S2]- and [ArP(OtBu)S2]- are reported (Ar = 4-anisyl). It is demonstrated that the topology of alkali metal ion and ligand composition influence the structure of supramolecular arrangements.     

Microporous polyphenylenes based on diacetylaromatic compounds

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Role of solvents in coordination supramolecular systems

Solvent effect is a vital subject in the domain of coordination chemistry. In this connection, previous researches mainly focus on the role of solvents in reaction kinetics and thermodynamics during the coordination processes. In virtue of the recent efforts on coordination supramolecular systems, especially coordination polymers or metal-organic frameworks, this feature article aims to demonstrate the solvent effect on regulating such diversiform metallosupramolecular solids, incorporating their crystal growth/assembly, structural modulation, dynamic transformations, and potential applications, which may provide new insights into the rational design and construction of such advanced crystalline materials.     

Enzyme mimics based upon supramolecular coordination chemistry

Recent advances in supramolecular coordination chemistry have allowed chemists to synthesize macromolecular complexes that exhibit various properties intrinsic to enzymes. This Review focuses on structures inspired by properties and functions observed in enzymes rather than precise models of enzyme active sites. These structures are synthesized using convergent, modular, and high-yielding coordination-chemistry-based methods, which allow one to tailor the size, shape, and properties of the resulting complexes. Many of the structures discussed exhibit reactivity and specificity reminiscent of natural systems, and some of them have functions that exceed the natural systems which provided the inspiration for initially making them.     

Metals and coordination compounds as modifiers for epoxy resins

This review concentrates on the use of metals in the formulation of epoxy resin systems and the effect that this has on the physical and mechanical properties of the polymer system. Epoxy resins are one of the most important higher performance polymer systems in use today, ranging from simple two-part adhesives and sports equipment to high-tech applications such as formula one racing cars and the aerospace industry. Epoxy resins are capable of undergoing homopolymerisation, although this process generally yields products with inadequate properties for high-tech applications. Consequently, in many cases catalysts, additives and co-curing-agents are formulated with the epoxy resin to significantly increase the storage stability, decrease the cure time and improve the final properties. The use of metals to formulate resin systems with excellent storage stability is discussed, along with the use of coordination compounds to improve cured resin properties such as fracture toughness, thermal stability and water absorption, etc.     

Co-crystallizing coordination compounds

Crystallization of an equimolar mixture of 1,10-dimethylphenanthroline (DMP) and manganese(II) chloride from N,N-dimethylformamide (DMF) has been studied. Rather than a useful route to a well-defined product, it was found that identical solutions could deposit crystals of three different compounds. The most common outcome was the formation of crystals of [MnCl₂(dmp)(dmf)], 1, or co-crystallization of [MnCl₂(dmp)(dmf)] and [{MnCl₂(dmp)}₂]. The co-crystals, 2, were always found to dissolve as crystals of 1 started to grow. Crystals of a third compound, [MnCl₂(dmp)₂], 3, were also isolated once.     

Lanthanide complexes with oda, ida, and nta: From discrete coordination compounds to supramolecular assemblies

Lanthanide metal–organic frameworks have been receiving special attention for the last decade. The use of polydentate organic ligands has allowed the construction of interesting network topologies with many potential applications, based on the special characteristics of the 4f electrons. In this paper, the structural and thermodynamic properties of Ln(III) complexes with oxydiacetate, iminodiacetate, and nitrilotriacetate are critically reviewed. The presence of ligands able to act as a bridge promotes the formation of Ln–M polynuclear complexes with fascinating 3D structures, whose study is also included. Equilibrium data of these systems in aqueous solution have been collected, showing the relationship between the composition of the species in solution and the nuclearity in the solid state.     

Novel silver-containing supramolecular frameworks constructed by combination of coordination bonds and supramolecular interactions

The hydrothermal reactions of AgNO(3), 4,4'-bipy, and carboxylate ligands gave rise to three supramolecular architectures, namely [Ag(bipy)].H(2)SIPA.1/2bipy.H(2)O (1), [Ag(bipy)].1/2H(2)btec.H(2)O (2), and [Ag(bipy)](2).H(2)dpstc.2H(2)O (3) (H(3)SIPA = 5-sulfoisophthalic acid, bipy = 4,4'-bipyridine, H(4)btec = 1,2,4,5-benzenetetracarboxylic acid, H(4)dpstc = 3,3',4,4'-tetracarboxydiphenyl sulfone). All complexes are extended from Ag-bipy linear chains by the combination of coordination bonds and supramolecular interactions in two different approaches. Complexes 1 and 3 comprise two-dimensional frameworks. In the two complexes, a one-dimensional ladderlike structure is first formed by the connection of a Ag-bipy chain through hydrogen bonding between a free carboxylate/bipy ligand and weak coordinative interactions between a free carboxylate ligand and silver ion. The ladderlike structure is then extended to a two-dimensional layer architecture by pi...pi interactions between bipy ligands of the Ag-bipy chains. Complex 2 possesses a three-dimensional framework. The free H(2)btec(2)(-) ligands form a two-dimensional layer network by hydrogen-bonding interactions between protonated and deprotonated carboxylate groups; meanwhile, pi.pi interactions between bipy ligands of Ag-bipy chains also result in a two-dimensional layer. The two layers are further connected by weak Ag-O interactions to generate a three-dimensional supramolecular structure.     

Ion spray-tandem mass spectrometry of supramolecular coordination complexes

Double-helical [M₂L₂] ⁿ⁺, triple-helical [M₂L₃] ⁿ⁺, and toroidal [M₃L₃] ⁿ⁺ (M = Cu, Co, Fe, Ni, La, Eu, Gd, Tb, or Lu) supramolecular complexes have been fully characterized by ion spray mass spectrometry (IS-MS). The IS-MS spectra from pure acetonitrile solutions reflect the nature of the cations present in solution with conservation of the charge state and allow an efficient qualitative speciation of the compounds. The mass spectrometry results can be correlated with other powerful techniques (nuclear magnetic resonance and electronic spectroscopy) for the characterization of supramolecular complexes in solution, Structural information is obtained by collision-induced dissociation, which strongly depends on the metal ions used in the supramolecular complexes and on the various connectivities and topologies of the ligands. When the ligand contains 3,5dimethoxybenzyl groups bound to the benzimidazole rings, the partial fragmentation of the complexes is associated with a decrease of the total charge of the complexes and the appearance of the characteristic fragment at m/z 151 that corresponds to the 3,5-dimethoxybenzyl cation. A detailed analysis of the fragmentation pathways of these supramolecular complexes suggests that the metal-nitrogen coordination bonds are very strong in the gas phase.     

Template-directed supramolecular self-assembly of coordination dumbbells at surfaces

Scanning tunneling microscopy reveals, at single-molecular resolution, how external parameters--substrate morphology and guest addition--re-direct the assembly of dumbbell-shaped coordination supramolecules towards different surface-confined supramolecular organizations.     

Stability of supramolecular compounds under heating

The decomposition of series of supramolecular compounds, namely inclusion compounds, was studied by means of different thermoanalytical methods, i.e., traditional thermogravimetry, quasi-equilibrium thermogravimetry, and thermomechanical analysis. The series of compounds included the intercalates on the base of fluorinated graphite C₂F, the clathrates on the base of carbamide and on the base of coordination compounds and microporous inclusion compounds on the base of coordination compounds. Kinetic parameters of decomposition processes were estimated within the approaches of the non-isothermal kinetics (“model-free” kinetics, linear and non-linear regression methods for the topochemical equation detection). The kinetic stability of the inclusion compounds under heating, the flexibility of the matrix structure, and the thermodynamic stability of the intermediate phases are discussed.     

Microporous niobium phosphates and catalytic properties prepared by a supramolecular templating mechanism

Microporous hexagonal niobium phosphate synthesized using neutral surfactants of molecular length, C6 to C10 hydrocarbons, by a supramolecular templating mechanism (S0I0) possesses strong hydrophilic character, which leads to high selectivity for catechol formation (95.3%) in the presence of protic solvent (MeOH) in the hydroxylation of phenol using aqueous H2O2.     

Thermal latent coordination compounds

Complexes of the type M(Pa)₂(HAz)₂ and M(QA)₂(HAz)₂ (M=cobalt(II) and nickel(II); HPa=picolinic acid, HQa=quinaldic acid; HAz=azoles like imidazole (Him), pyrazole (HPz), benzimidazole (HBzIm) etc.) show a similar thermal behaviour. In the first step of decomposition the corresponding azolinium picolinates or quinaldinates (H₂AzPa, H₂AzQa) are split off with formation of polymeric mixed ligand complexes M(Pa)(Az) or M(Qa)(Az). X-ray analysis of Co(Qa)₂(HBzIm)₂ XIIIa illustrates a proton transfer and a subsequent thermal removal of benzimidazolinium quinaldinate (H₂BzImQa): Hydrogen bridges from pyrrole nitrogen of the benzimidazole to the non-coordinated oxygen of the quinaldinate predetermine the thermal initiated proton transfer. The high volatility of the heterocyclic acids and the nitrogen coordination are responsible for the formation of the mixed ligand complex Co(Qa)(BzIm) XIVa. Exceptions are the complexes M(Pa)₂(HPz)₂ XIa-b and M(Qa)₂(HIm)₂ XVIIa-b. Pyrazole is eliminated from the complexes XIa-b with formation of the solvent-free inner complex M(Pa)₂ XIIa-b. From compounds XVIIIa-b quinaldic acid or their decomposition products are split off and a high temperature modification of M(Im)₂ XVIIIa-b is formed at elevated temperature. XVIIIa-b are decomposed to the cyanides M(CN)₂ similarly to the thermal behaviour of Cu(Im). In the first step the thermal degradation of imidazole and pyrazole adducts of copper(II) picolinates and quinaldinates is characterized by the elimination of azoles. The reason for this thermal behaviour is the weaker coordination of the azole heterocycles in copper chelate compounds.     

Thermal latent coordination compounds

The thermal behaviour of complexes of the type M(HIm)₂ac₂ (HIm=imidazole,ac=acetate,M=Co, Ni, Cu) is different. Comparable to the thermal degradation of Ni(acac)₂(HIm)₂ [10] the Ni(HIm)₂ac₂ loss acetic acid by formation of Ni(Im)₂. All nitrogen ligands are splitt off from the copper complex by formation of stable basic copper acetate. The cobalt compound eliminated acetic acid partially while acetate and imidazolate bridging species are obtained. The thermal behaviour of the acetate complexes of pyrazole and the bulky 3,5-dimethylpyrazole is quite similar. In a first step pyrazoliumacetate is removed. The crystal structure of Ni(HPz)₄ac₂ is determined by X-ray diffraction: monocline, space group C 2/c. The water molecule represents the centre of two N?H...O?H...O-bridges. The system of H-bridges in the compound relieves the proton transfer, indicated by the elimination of pyrazolium acetate.     

Microporous pillared paddle-wheel frameworks based on mixed-ligand coordination of zinc ions

The reaction of Zn(NO3)2 x 6H2O, various dicarboxylic acids, and either 4,4'-bipyridine or N,N'-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide produces a family of anisotropic, mixed-ligand, open-framework compounds featuring paddle-wheel-type coordination of Zn(II) pairs in two dimensions and pyridyl ligand pillaring in the third. Despite 2-fold interpenetration, the compounds contain channels of molecular dimensions and several are permanently microporous, displaying high internal surface areas.     

Ultrasound-assisted nanoscaled supramolecular coordination polymer as an efficient recyclable catalyst for photocatalytic degradation of dye pollutants

An ultrasound-assisted nanoscaled supramolecular coordination polymer (nanosized 1′ ) has been synthesized using a self-assembly reaction of K₃[Cu (CN)₄] and hexamethylenetetramine in the presence of Me₃SnCl under ambient conditions. Nanosized 1′ was examined using elemental analysis, Fourier transform–infrared, transmission electron microscopy, scanning electron microscopy and X-ray powder diffractions. It was structurally compared with the single crystal supramolecular coordination polymer ^∞₃[Cu₆(CN)₇(C₆H₁₂N₄)₂(OH₃)]; SCP 1. The photocatalytic activities of nanosized 1′ and SCP 1 toward different hazardous organic dyes were determined under ambient, UV-light irradiation and ultrasonic conditions. SCP 1 and nanosized 1′ as heterogeneous nanoparticles catalysts exhibited high catalytic activity for degradation of Congo Red, Methyl Violet 2B and Methylene Blue dyes. The effects of operational parameters on catalytic degradation process, identification of the degradation products and recycling of the catalyst were also investigated. SCP 1 and nanosized 1′ are recyclable heterogeneous catalysts and can be reused with efficient activities. The mechanism of degradation using different scavenger techniques iss proposed and discussed. The catalytic oxidation process is mainly caused by ^•OH radicals.