Controlled polymerization and self-assembly of halogen-bridged diruthenium complexes in organic media and their dielectrophoretic alignment

Adenine selected hydrogelation of vitamin B2 with amplified circularly polarized luminescence

Although the individual VB2 cannot form gels in water, it could form a two-component hydrogel with adenine (A) through the intermolecular π-π stacking and hydrogen bonding between VB2 and A, while other nucleobases, including thymine (T), guanine (G), cytosine (C) and uracil (U), could not. The chiral information of VB2 was amplified in the co-assembly of VB2 and A, which was revealed by the enhanced circular dichroism (CD) and circularly polarized luminescence (CPL). Moreover, due to the different interaction modes between VB2 and A in 1 : 1 and 1 : 2 molar ratio, a reversion of the CPL signal was observed. This work demonstrated how biological molecules could be fabricated into functional materials using the specific interactions within the biological molecules.

Electrochemical atomic force microscopy of two-dimensional trinuclear ruthenium clusters molecular assembly and dynamics under redox state control

Mixed-valence ruthenium trinuclear clusters containing dichloroacetates were synthesized, and the self-assembly of a single molecular adlayer composed of these clusters on a graphite surface was investigated by atomic force microscopy (AFM). AFM clearly revealed the dynamics of two-dimensional (2D) structure formation as well as the molecular characteristics of the adlayers at different electrochemical interfaces. The results verified that the design of metal complexes is important not only for redox chemistry but also for molecular assembly and nanoarchitecture construction.

Supramolecular Helical Assemblies of Dirhodium(II) Paddlewheels with 1,4-Diazabicyclo[2.2.2]octane: A Remarkable Substituent Effect on the Helical Sense Preference and Amplification of the Helical Handedness Excess of Metallo-Supramolecular Helical Polymers

We report unique coordination-driven supramolecular helical assemblies of a series of dirhodium(II) tetracarboxylate paddlewheels bearing chiral phenyl- or methyl-substituted amide-bound m-terphenyl residues with triethylene glycol monomethyl ether (TEG) or n-dodecyl tails through a 1:1 complexation with 1,4-diazabicyclo[2.2.2]octane (DABCO). The chiral dirhodium complexes with DABCO in CHCl₃/n-hexane (1:1) form one-handed helical coordination polymers with a controlled propeller chirality at the m-terphenyl groups, which are stabilized by intermolecular hydrogen-bonding networks between the adjacent amide groups at the periphery mainly via a cooperative nucleation-elongation mechanism as supported by circular dichroism (CD), vibrational CD, and variable-temperature (VT) absorption and CD analyses. The VT visible-absorption titrations revealed the temperature-dependent changes in the degree of polymerization. The columnar supramolecular helical structures were elucidated by X-ray diffraction and atomic force microscopy. The helix sense of the homopolymer carrying the bulky phenyl and n-dodecyl substituents is opposite those of other chiral homopolymers despite having the same absolute configuration at the pendants. A remarkably strong "sergeants and soldiers" (S&S) effect was observed in most of the chiral/achiral copolymers, while the copolymers of the bulky chiral phenyl-substituted dirhodium complexes with n-dodecyl chains displayed an "abnormal" S&S effect accompanied by an inversion of the helix sense, which could be switched to a "normal" S&S effect by changing the solvent composition. A nonracemic dirhodium complex of 20% enantiomeric excess bearing the less bulky chiral methyl substituents with n-dodecyl chains assembled with DABCO to form an almost one-handed helix (the "majority rule" (MR) effect), whereas the three other nonracemic copolymers showed a weak MR effect.

Improving the Solubility of Hexanuclear Heterometallic Extended Metal Atom Chain Compounds in Nonpolar Solvents by Introducing Alkyl Amine Moieties

The highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) interaction at the d _{z ²} orbital between two kinds of metal complex is useful for obtaining heterometallic one-dimensional (1D) chains as well as heterometallic metal string compounds (HMSCs). Platinum dinuclear complexes, [Pt₂(piam)₂(NH₂R)₄]X₂ (piam = pivalamidate, R = CH₃, C₂H₅, C₃H₇, or C₄H₉, X = anion), comprising σ* as HOMO were mixed with [Rh₂(O₂CCH₃)₄] comprising σ* as LUMO in solvents to afford single crystals of [{Rh₂(O₂CCH₃)₄}{Pt₂(piam)₂(NH₂R)₄}₂]X₄ (2-5). Single-crystal X-ray analyses revealed that 2-5 are hexanuclear complexes that are one-dimensionally aligned as Pt-Pt-Rh-Rh-Pt-Pt with metal-metal bonds, where the alkyl moieties at end Pt atoms obstruct further 1D extension. Complexes 2-5 appear as if they are cut off from an infinite chain [{Rh₂(O₂CCH₃)₄}{Pt₂(piam)₂(NH₃)₄}₂] _n (PF₆)_4n ·6nH₂O (1) aligned as -{Pt-Pt-Rh-Rh-Pt-Pt} _n -. The diffuse reflectance spectrum of 1 depicts broad shoulder bands, which are not present in the spectra of 2-5, proving that the infinite chain 1 forms a band structure. Compounds 4 and 5 with propyl or butyl moieties at amine ligands, respectively, are soluble in nonpolar solvents, such as CH₂Cl₂, without the dissociation of their hexanuclear structures. Taking advantage of their solubility, measurement of cyclic voltammetry in CH₂Cl₂ become possible, which shows the quasi-reversible oxidation and reduction waves at 4: E _ox = 0.86 V and E _red = 0.69 V and 5: E _ox = 0.87 V and E _red = 0.53 V.

Two Orthogonal Halogen-Bonding Interactions Directed 2D Crystalline Supramolecular J-Dimer Lamellae

Dye assemblies exhibit fascinating properties and performances, both of which depend critically on the mutual packing arrangement of dyes and on the supramolecular architecture. Herein, we engineered, for the first time, an intriguing chlorosome-mimetic 2D crystalline J-dimer lamellar structure based on halogenated dyes in aqueous media by employing two distinct orthogonal halogen-bonding (XB) interactions. As the only building motif, antiparallel J-dimer was formed and stabilized by single π-stacking and dual halogen⋅⋅⋅π interactions. With two substituted halogen atoms acting as XB donors and the other two acting as acceptors, the constituent J-dimer units were linked by quadruple highly-directional halogen⋅⋅⋅halogen interactions in a staggered manner, resulting in unique 2D lamellar dye assemblies. This work champions and advances halogen-bonding as a remarkably potent tool for engineering dye aggregates with a controlled molecular packing arrangement and supramolecular architecture.

Nematic-to-columnar mesophase transition by in situ supramolecular polymerization

Disk- and rod-shaped molecules are incompatible in coassembly, as the former tend to stack one-dimensionally whereas the latter tend to align in parallel. Because this type of incompatibility can be more pronounced in condensed phases, different-shaped molecules generally exclude one another. We report that supramolecular polymerization of a disk-shaped chiral monomer in nematic liquid crystals comprising rod-shaped molecules results in order-increasing mesophase transition into a single mesophase with a core-shell columnar geometry. This liquid crystalline material responds quickly to an applied electric field, resulting in unidirectional columnar ordering. Moreover, it can be modularly customized to be optoelectrically responsive simply by using a photoisomerizable rod-shaped module. The modular strategy allows for cooperative integration of different functions into elaborate dynamic architectures.

Paddlewheel-type diruthenium(iii,iii) tetrakis(2-aminopyridinate) complexes with NIR absorption features: combined experimental and theoretical study

Aminopyridinate-bridged Ru₂(iii,iii) complexes with near-infrared absorption features were prepared and characterized by experimental and theoretical techniques.

Electroactive Amphiphiles for Addressable Supramolecular Nanostructures

In this focus review we aim to highlight an exciting class of materials, electroactive amphiphiles (EAAs). This class of functional amphiphilic molecules has been the subject of sporadic investigations over the last few decades, but little attempt has been made to date to gather or organise these investigations into a logical fashion. Here we attempted to gather the most important contributions, provide a framework in which to discuss them, and, more importantly, point towards the areas where we believe these EAAs will contribute to solving wider scientific problems and open new opportunities. Our discussions cover materials based on low molecular weight ferrocenes, viologens and anilines, as well as examples of polymeric and supramolecular EAAs. With the advances of modern analytical techniques and new tools for modelling and understanding optoelectronic properties, we believe that this area of research is ready for further exploration and exploitation.

Photoirradiation-generated radicals in two-component supramolecular gel for polymerization

While supramolecular gels have been attracting great interest due to their easy design and fabrication, development of new applications based on these gels is always a challenging topic. Here, we report a two-component supramolecular gel that can generate and stabilize radicals through photo-irradiation, which can be subsequently used for polymerization. It has been found that the electrostatic interactions between a cationic amphiphile and anionic sulfonate could afford co-assembly into a two-component supramolecular gel. Upon photo-irradiation, the gel changed colour and produced the radicals, as verified from the EPR measurements. The radical thus formed in the supramolecular gel is relatively stable and could be used to polymerize acrylic acid directly without deoxygenation. In contrast, acrylic acid could not be polymerized in solution under the same conditions. This work expands the application scope of supramolecular gels.

Hierarchical Self-Assembly of Luminescent Tartrate-Bridged Chiral Binuclear Tb(III) Complexes in Ethanol

A new family of supramolecular metalloamphiphiles carrying two metal centers is developed. They are formed by bridging two coordinatively unsaturated lipophilic Tb³⁺ complexes (TbL⁺) with chiral dicarboxylate anions. The formation of bridging coordination bonds is confirmed using UV spectroscopy, induced circular dichroism (ICD), increased luminescence intensity of TbL⁺, and electrospray ionization mass spectrometry (ESIMS) analysis. These supramolecular metalloamphiphiles hierarchically self-assemble in ethanol to give luminescent nanospheres, as observed using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The two hydroxyl groups introduced in the bridging ligands of [TbL]₂(d-/l-tartrate) significantly promote self-assembly by increasing coherent forces via intermolecular hydrogen bonding. The observed self-assembly in ethanol also merits mention because such polar alcoholic media have been unfavorable for conventional molecular self-assemblies. The present approach offers a new molecular design strategy for composable metalloamphiphiles.

One-dimensional coordination polymers of [Co3(dpa)4](2+) and [MF6](2-) (M = Re(IV), Zr(IV) and Sn(IV))

One-dimensional coordination polymers of alternating metal-metal bonded trinuclear [Co3(dpa)4](2+) (dpa = the anion of 2,2'-dipyridylamine) building blocks and [ReF6](2-) (1), [ZrF6](2-) (2) or [SnF6](2-) (3) linkers have been self-assembled and crystallographically characterized. Magnetic measurements reveal a significant ferromagnetic coupling (J/k(B) = +9.9 K) between S = 1/2 {Co3(6+)} and S = 3/2 Re(IV) magnetic sites through a single, unsupported fluoride bridge in 1.

Platinum(II)-Based Metallo-Supramolecular Polymer with Controlled Unidirectional Dipoles for Tunable Rectification

A platinum(II)-based, luminescent, metallo-supramolecular polymer (PolyPtL1) having an inherent dipole moment was synthesized via complexation of Pt(II) ions with an asymmetric ligand L1, containing terpyridyl and pyridyl moieties. The synthesized ligand and polymer were well characterized by various NMR techniques, optical spectroscopy, and cyclic voltammetry studies. The morphological study by atomic force microscopy revealed the individual and assembled polymer chains of 1-4 nm height. The polymer was specifically attached on Au-electrodes to produce two types of film (films 1 and 2) in which the polymer chains were aligned with their dipoles in opposite directions. The Au-surface bounded films were characterized by UV-vis, Raman spectroscopy, cyclic voltammetry, and atomic force microscopy study. The quantum mechanical calculation determined the average dipole moment for each monomer unit in PolyPtL1 to be about 5.8 D. The precise surface derivatization permitted effective tuning of the direction dipole moment, as well as the direction of rectification of the resulting polymer-attached molecular diodes. Film 1 was more conductive in positive bias region with an average rectification ratio (RR = I(+4 V)/I(-4 V)) ≈ 20, whereas film 2 was more conducting in negative bias with an average rectification ratio (RR = I(-4 V)/I(+4 V)) ≈ 18.

Supramolecular chemistry of metal complexes in solution

Building on established supramolecular chemistry, metal coordination and organometallic chemistry have been widely explored for supramolecular polymers and nanostructures. Increasingly, research has demonstrated that this approach is promising for the synthesis of novel materials with functions and properties derived from metal elements and their coordination structures. Unique self-assembling behaviour and unexpected supramolecular structures are frequently discovered due to multiple non-covalent interactions in addition to metal coordination. However, an explicit understanding of the synergistic effects of non-covalent interactions for designed synthesis of metal containing assemblies with structure correlated properties remains a challenge to be addressed. Recent literature in the area is highlighted in this review in order to illustrate newly explored concepts and stress the importance of developing well understood and controlled supramolecular chemistry for designed synthesis.

Simulation of mesogenic diruthenium tetracarboxylates: Development of a force field for coordination polymers of the MMX type

A classical molecular mechanics force field, able to simulate coordination polymers (CP) based on ruthenium carboxylates (Ru2 (O2CReq )4 Lax) (eq = equatorial group containing aliphatic chains, Lax = axial ligand), has been developed. New parameters extracted from experimental data and quantum calculations on short aliphatic chains model systems were included in the generalized AMBER force field. The proposed parametrization was evaluated using model systems with known structure, containing either short or long aliphatic chains; experimental results were reproduced satisfactorily. This modified force field, although in a preliminary stage, could then be applied to long chain liquid crystalline compounds. The resulting atomistic simulations allowed assessing the relative influence of the factors determining the CP conformation, determinant for the physical properties of these materials.

Comparative study of different methods for the preparation of tetraamidato- and tetracarboxylatodiruthenium compounds. Structural and magnetic characterization

Solvothermal and microwave assisted synthesis were used as green and very useful alternative methods to obtain new chloridotetraamidatodiruthenium compounds, [Ru(2)Cl(μ-NHOCR)(4)](n) [R = Me-o-C(6)H(4) (1), Me-m-C(6)H(4) (2), Me-p-C(6)H(4) (3)]. The analogous tetracarboxylato complexes [Ru(2)Cl(μ-O(2)CR)(4)](n) [R = Me-o-C(6)H(4) (4), Me-m-C(6)H(4) (5), Me-p-C(6)H(4) (6)] have also been obtained. These synthetic methods allow the use of greener solvents like water or ethanol. Moreover, solvothermal synthesis permits the direct crystallization of the desired complexes, which are extremely insoluble in common solvents, during the synthetic process. Therefore, the crystal structure of all of them has been established using single crystal X-ray diffraction. Complex 1 shows a Ru-Cl-Ru angle of 180° and constitutes the first example of a chloridotetraamidatodiruthenium derivative displaying linear chains in the solid state. In contrast, complexes 2·0.5EtOH, and 3-6 show polymeric arrangements with the diruthenium units linked by chloride ligands, forming zigzag chains with Ru-Cl-Ru angles ranging between 117.03(6) and 121.45(3)°. All of the complexes show magnetic moments at room temperature corresponding to three unpaired electrons in agreement with the σ(2)π(4)δ(2)(π*δ*)(3) ground-state configuration, which indicates a similar magnetic behaviour in amidato and carboxylato derivatives. In the linear arrangement of complex 1 there is a better magnetic communication between diruthenium units (antiferromagnetic coupling, zJ = -10.5 or -8.7 cm(-1)) than the one observed in the zigzag 2-6 complexes (zJ = -1.23 to -5.75 cm(-1)).