When Cu4I4 cubane meets Cu3(pyrazolate)3 triangle: dynamic interplay between two classical luminophores functioning in a reversibly thermochromic coordination polymer

A supramolecular dual emissive system incorporating two classical copper(I)-cluster-based luminophores, namely, Cu(4)I(4) and Cu(3)Pz(3) (Pz = pyrazolate), is reported. The targeted luminescent coordination polymer exhibits reversible thermochromism spanning from green to orange-red.     

Metal-mediated Discrete Supramolecular Assemblies of Porphyrins

There is substantial recent interest worldwide in the construction of multiporphyrin assemblies which can either mimic naturally occurring multichromophore aggregates, such as the photosynthetic reaction center and the light harvesting complex of purple bacteria, or which can be used as electron- and/or energy-transfer molecular devices for advanced technological tasks. The metal-mediated self-assembly approach, which exploits the formation of coordination bonds between peripheral basic site(s) on the porphyrins and metal centers, has recently allowed the design and preparation of sophisticated supramolecular architectures whose complexity and function begin to approach the properties of naturally occurring systems. Within this framework, meso -pyridyl/phenyl porphyrins (PyPs), or strictly related chromophores, can provide geometrically well-defined connections to as many as four metal centers by coordination of the pyridyl groups. Several discrete assemblies of various nuclearities, in which the pyridylporphyrins are linkers binding metalloporphyrins and/or coordination compounds, have been constructed in recent years. Our contribution to this field is reviewed, with the aim of providing insight into the design of new, more elaborated architectures of higher order.     

Self-Assembly of Highly Stable Zirconium(IV) Coordination Cages with Aggregation Induced Emission Molecular Rotors for Live-Cell Imaging

The self-assembly of highly stable zirconium(IV)-based coordination cages with aggregation induced emission (AIE) molecular rotors for in vitro bio-imaging is reported. The two coordination cages, NUS-100 and NUS-101, are assembled from the highly stable trinuclear zirconium vertices and two flexible carboxyl-decorated tetraphenylethylene (TPE) spacers. Extensive experimental and theoretical results show that the emissive intensity of the coordination cages can be controlled by restricting the dynamics of AIE-active molecular rotors though multiple external stimuli. Because the two coordination cages have excellent chemical stability in aqueous solutions (pH stability: 2–10) and impressive AIE characteristics contributed by the molecular rotors, they can be employed as novel biological fluorescent probes for in vitro live-cell imaging.     

From Molecular Diversity to Template-Directed Self-Assembly – New Trends in Metallo-Supramolecular Chemistry

Molecular diversity can easily be generated in metallo-supramolecular systems by simple mixing of oligodentate ligands and appropriate metal ions. In this reaction either a defined coordination compound is formed in a selective self-assembly process or a mixture is obtained. Depending on the system such a mixture can possess a statistical distribution of components or the formation of some species is thermodynamically favored leading to only a few out of several possible compounds (or in the extreme to only one). Simple well-defined mixtures containing only a few components or pure supramolecular aggregates can be generated from sequential or directional ligands, from mixtures of ligands and/or metals, and by introducing templates which support the formation of defined metallo-supramolecular aggregates. In the latter case it is possible first to generate a mixture of components which are in dynamic equilibrium (dynamic combinatorial library). In a second step, a template can be added, which in a dynamic process transforms such a library into one well-defined species. Thus, the initial generation of molecular diversity allows in a subsequent selection step in an evolutionary process the formation of the most favored receptor/substrate adduct (``dynamic combinatorial chemistry').     

Structural Determination of an Unusual CuI-Porphyrin-π-Bond in a Hetero-Pacman Cu-Zn-Complex

The synthesis and characterization of a hetero-dinuclear compound is presented, in which a copper(I) trishistidine type coordination unit is positioned directly above a zinc porphyrin unit. The close distance between the two coordination fragments is secured by a rigid xanthene backbone, and a unique (intramolecular) copper porphyrin-π-bond was determined for the first time in the molecular structure. This structural motif was further analyzed by temperature-dependent NMR studies: In solution at room temperature the coordinative bond fluctuates, while it can be frozen at low temperatures. Preliminary reactivity studies revealed a reduced reactivity of the copper(I) moiety towards dioxygen. The results adumbrate why nature is avoiding metal porphyrin-π-bonds by fixing reactive metal centers in a predetermined distance to each other within multimetallic enzymatic reaction centers.     

Self-assembly of a bis-porphyrinic supramolecular rectangle using two orthogonal binding strategies

A bis-porphyrinic rectangle is created via a double self-assembly algorithm using two orthogonal coordination themes, i.e. first a 90 degrees building block composed of a dynamic heteroleptic Cu(I) or Ag(I) bisphenanthroline followed by a coordinative dimerization using the pyridine-zinc porphyrin motif; the spectroscopic and electrochemical properties as well as the dynamic nature of the supramolecule were tested.     

Ligand design for alkali-metal-templated self-assembly of unique high-nuclearity CuII aggregates with diverse coordination cage units: crystal structures and properties

The construction of two unique, high-nuclearity Cu(II) supramolecular aggregates with tetrahedral or octahedral cage units, [(mu(3)-Cl)[Li subset Cu(4)(mu-L(1))(3)](3)](ClO(4))(8)(H(2)O)(4.5) (1) and [[Na(2) subset Cu(12)(mu-L(2))(8)(mu-Cl)(4)](ClO(4))(8)(H(2)O)(10)(H(3)O(+))(2)](infinity) (2) by alkali-metal-templated (Li(+) or Na(+)) self-assembly, was achieved by the use of two newly designed carboxylic-functionalized diazamesocyclic ligands, N,N'-bis(3-propionyloxy)-1,4-diazacycloheptane (H(2)L(1)) or 1,5-diazacyclooctane-N,N'-diacetate acid (H(2)L(2)). Complex 1 crystallizes in the trigonal R3c space group (a = b = 20.866(3), c = 126.26(4) A and Z = 12), and 2 in the triclinic P1 space group (a = 13.632(4), b = 14.754(4), c = 19.517(6) A, alpha = 99.836(6), beta = 95.793(5), gamma = 116.124(5) degrees and Z = 1). By subtle variation of the ligand structures and the alkali-metal templates, different polymeric motifs were obtained: a dodecanuclear architecture 1 consisting of three Cu(4) tetrahedral cage units with a Li(+) template, and a supramolecular chain 2 consisting of two crystallographically nonequivalent octahedral Cu(6) polyhedra with a Na(+) template. The effects of ligand functionality and alkali metal template ions on the self-assembly processes of both coordination supramolecular aggregates, and their magnetic behaviors are discussed in detail.     

X-ray structures,photophysical characterization,and computational analysis of geometrically constrained copper(I)--phenanthroline complexes

A series of three geometrically constrained C(2)-symmetric Cu(I) mono-phenanthroline complexes were characterized by X-ray structural analysis, and their photophysical properties were investigated by absorption and emission spectroscopy. Visible light excitation yielded metal-to-ligand charge-transfer (MLCT) excited states with luminescence lifetimes up to 155 ns. Ultrafast transient absorption spectroscopy provided further insights into the excited-state dynamics and suggests for all three complexes the formation of a phenanthroline radical anion. In agreement with electrochemical measurements, the data further indicate that coordinative rearrangements are involved in nonradiative deactivation of the excited states. According to time-dependent density functional theory calculations (B3LYP/6-31G), the major MLCT transitions are polarized along the C(2) axis of the complex and originate predominantly from the copper d(xz) orbital. The computational analysis identifies an excited-state manifold with a number of close-lying, potentially emissive triplet states and is in agreement with the multiexponential decay kinetics of the MLCT luminescence. The relationship between structural and photophysical data of the studied Cu(I) mono-phenanthroline complexes agrees well with current models describing the photophysics of the related Cu(I) bis-diimine complexes.     

Coordination-Induced Emission from Tetraphenylethylene Units and Their Applications

Thanks to the potential of aggregation-induced emission (AIE) phenomena, improved stabilities, and the good selectivity and sensitivity of the chemical responses exhibited by the products, coordination-driven self-assembly with tetraphenylethylene (TPE) units has recently received much attention and has been widely investigated for application in chemical sensors, cell imaging agents, light-harvesting systems, and others. Several reviews have emerged on the topics of AIE chemistry and aggregation-induced emission luminogen (AIEgen)-based supramolecular assembles, however, there is still a distinct lack of full overviews of emission enhancement from the viewpoint of metal-coordination effects. Thus, this minireview offers recent advances that have been made in the design and application of TPE-based metallacycles, metallacages, metal-organic frameworks (MOFs) and coordination polymers (CPs).     

Saccharinate as a versatile polyfunctional ligand. Four distinct coordination modes, misdirected valence, and a dominant aggregate structure from a single reaction system

The reaction system consisting of copper, saccharinate, and the auxiliary ligands H(2)O, PPh(3), and NH(3) produces a sequence of compounds in which saccharinate is coordinated to copper in four distinct manners. The complex trans-[Cu(sacch)(2)(H(2)O)(4)] (2) (produced by thermal dehydration of trans-[Cu(sacch)(2)(H(2)O)(4)].2H(2)O (1)) reacts with triphenylphosphine in CH(2)Cl(2) to produce any or all of three Cu(I) complexes, depending upon conditions. The three Cu(I) compounds are Cu(sacch)(PPh(3))(3) (3), in which saccharinate binds to copper through the carbonyl group of the ligand, Cu(sacch)(PPh(3))(2) (4), in which sacch binds to Cu through its charge-bearing nitrogen atom; and [Cu(sacch)(PPh(3))](2) (5), a dinuclear complex in which saccharinate bridges two Cu centers through its imidate nitrogen and carbonyl oxygen atoms. Complexes 3-5 can be isolated individually, although in solution they exist in a complex equilibrium which has been examined by NMR spectroscopy. Each of the three Cu(I) products reacts with NH(3) in CH(2)Cl(2) solution to produce trans-[Cu(sacch)(2)(NH(3))(4)] (6), an unstable Cu(II) complex that exhibits misdirected valence at the Cu-N(sacch) bond. Complex 6 evolves spontaneously to [Cu(sacch)(NH(3))(4)](sacch).H(2)O (7), which in the solid state is dominated by a supramolecular aggregate of two formula units, linked by hydrogen bonding in which the water molecule plays a central role. Alternative pathways exist to several of the products. The X-ray crystal structure analyses of 3-7 are reported and establish the coordination modes of saccharinate, the misdirected valence in 6, and the supramolecular aggregation in 7. The structure analysis of 7 by single-crystal neutron diffraction is reported and together with the previously reported neutron structure analysis of 1 establishes the substitution of the auxiliary ligand H(2)O by NH(3) in the Cu(II) products.     

Remote control of the reversible assembly/disassembly of supramolecular aggregates

ABSTRACT

A multi-component system is presented in which the actuation of a copper-loaded nanoswitch by zinc(II) ions as an external trigger and the thereby prompted release of copper(I) ions allows self-assembly of 11 parts resulting in the formation of a three-component supramolecular prism. Using the same protocol, a three-component rectangle was made from eight parts. Disassembly of the aggregates was accomplished by selective removal of zinc(II) ions using hexacyclen. In sum, the reversible assembly and disassembly of supramolecular aggregates was controlled in a multi-component mixture through intermolecular communication using a second messenger.     

Structural diversity in coordination self-assembled networks of a multimodal ligand azacalix[4]pyrazine

We report herein the synthesis of a new heteracalixaromatic compound, tetramethylazacalix[4]pyrazine (TAPz), and its coordination self-assemblies with metal and metal cluster centers. Structural characterization of TAPz has shown that its conformation is fluxional in solution but exhibits a dominant 1,3-alternate configuration in the crystalline solid state, wherein its convergent chelating coordination sites are orthogonal to the 120°-angled bridging sites, thus forming a unique multimodal ligand. Compound TAPz reacting with silver, zinc metal centers, and Cu(x)I(x) cluster centers leads to the construction of diverse coordination network structures in 1-5 including honeycomb, Kagomé, α-quartz, and cavity-involved two-dimensional layers. The structural diversity of these network structures is conducted by different combination modes between the chelation bonding sites of TAPz and metal or metal cluster centers. This system may afford deeper insight on the fantastic use of macrocyclic compounds on the designed synthesis of coordination network structures through the proper arrangement of their coordination sites.     

席夫碱Cu(Ⅱ)络合物的超分子螺旋手性及其手性光谱

本文通过不同的手性二胺(pn=1,2-丙二胺、chxn=1,2-环己二胺、dpen=1,2-二苯基乙二胺)与脱氢乙酸(dha)缩合,获得了N_2O_2型手性席夫碱配体(dha-en),进而合成了相应的三对手性席夫碱Cu(Ⅱ)络合物([Cu(dha-R/S-pn)](1a和1b)、[Cu(dha-R,R/S,S-chxn)](2a和2b)、[Cu(dha-R,R/S,S-dpen)](3a和3b),对其进行的固体和溶液电子圆二色(ECD)及溶液振动圆二色(VCD)光谱测试表明,这些化合物在固体和溶液状态下的金属中心的主要配位模式和绝对构型基本一致。此外,通过单晶结构分析发现:对于络合物2a/2b以及3a/3b,中心金属Cu(Ⅱ)除了与手性dha-en四齿配位外,还与相邻分子内酯环上的羰基发生弱的轴向配位形成一维超分子螺旋链,即实现了配位键构筑的席夫碱络合物的手性超分子自组装。本文对两对手性络合物2a/2b以及3a/3b的手性结构基元及其与超分子螺旋之间的关系进行了讨论。将本文所获实验VCD光谱数据与文献报道的相关数据进行比对分析,可以相互印证,并呈现一定的绝对构型关联规律且具有手性配位立体化学结构的指纹特征。     

Supramolecular chlorophyll aggregates inspired from specific light-harvesting antenna “chlorosome”: Static nanostructure,dynamic construction process,and versatile application

Photosynthetic light-harvesting antennas possess a variety of supramolecular structures with the same function (collecting sunlight energy), dependent on their living habitats and environments of phototrophs. Notably, the main antenna in green photosynthetic bacteria called “chlorosome” is structurally unique. Its core is constructed solely from self-aggregates of chlorophyll molecules without the support of any protein scaffolds. The supramolecular structures of the chlorophyll aggregates were already estimated, but have not been determined completely due to the natural diversity of chlorosomes. The static structures of chlorosomes are somewhat difficult to be characterized, and also the determination of their dynamic construction processes in vivo, such as their biogenesis and growth, is more challenging. Consequently, the measurement and observation of a simplified chlorosome model prepared by in vitro self-assembly of native or non-native (semisynthetic) chlorophylls are important. The present review focuses on evaluation of the static and dynamic nanostructures of chlorosomal aggregates. The construction, observation, and analysis of such models could be translated into the supramolecular aggregates of native chlorosomes. Additionally, synthetic aggregates display remarkable properties, which would be valuable for the development of solar cells and artificial photosynthesis. Such systems could potentially also be applied as photofunctional materials.     

Strong steric hindrance effect on excited state structural dynamics of Cu(I) diimine complexes

The metal-to-ligand-charge-transfer (MLCT) excited state of Cu(I) diimine complexes is known to undergo structural reorganization, transforming from a pseudotetrahedral D(2d) symmetry in the ground state to a flattened D(2) symmetry in the MLCT state, which allows ligation with a solvent molecule, forming an exciplex intermediate. Therefore, the structural factors that influence the coordination geometry change and the solvent accessibility to the copper center in the MLCT state could be used to control the excited state properties. In this study, we investigated an extreme case of the steric hindrance caused by attaching bulky tert-butyl groups in bis(2,9-di-tert-butyl-1,10-phenanthroline)copper(I), [Cu(I)(dtbp)(2)](+). The two bulky tert-butyl groups on the dtbp ligand lock the MLCT state into the pseudotetrahedral coordination geometry and completely block the solvent access to the copper center in the MLCT state of [Cu(I)(dtbp)(2)](+). Using ultrafast transient absorption spectroscopy and time-resolved emission spectroscopy, we investigated the MLCT state property changes due to the steric hindrance and demonstrated that [Cu(I)(dtbp)(2)](+) exhibited a long-lived emission but no subpicosecond component that was previously assigned as the flattening of the pseudotetrahedral coordination geometry. This suggests the retention of its pseudotetrahedral D(2d) symmetry and the blockage of the solvent accessibility. We made a comparison between the excited state dynamics of [Cu(I)(dtbp)(2)](+) with its mono-tert-butyl counterpart, bis(2-tert-butyl-1,10-phenanthroline)copper(I) [Cu(I)(tbp)(2)](+). The subpicosecond component assigned to the flattening of the D(2d) coordination geometry in the MLCT excited state was again present in the latter because the absence of a tert-butyl on the phenanthroline allows flattening to the pseudotetrahedral coordination geometry. Unlike the [Cu(I)(dtbp)(2)](+), [Cu(I)(tbp)(2)](+) exhibited no detectable emission at room temperature in solution. These results provide new insights into the manipulation of various excited state properties in Cu diimine complexes by certain key structural factors, enabling optimization of these systems for solar energy conversion applications.     

Dimensionally confined nanosheets self-assembled through self-shielding multiple hydrogen bonding interactions in aqueous media

Herein, we adopt a simple supramolecular strategy to effectively control the tautomerism of ureidopyrimidinone (UPy) moiety and ultimately realize the complete arrangement of enol configuration. The obtained UPy derivatives containing self-complementary quadruple hydrogen bonding interactions can spontaneously self-assemble towards the formation of well-controlled, self-organized supramolecular nanostructure morphologies in both chloroform and water. The resulting aggregates had been fully characterized by various spectroscopy (absorption, emission) and microscopy (TEM, SEM and AFM) studies. It is anticipated that this study can provide an exact and excellent monomeric unit for controllable and precise supramolecular polymerization. The results achieved here also demonstrate the utility and feasibility of multiple hydrogen bonds to direct the self-assembly of small-molecule building blocks in aqueous media, which provides a strategy for the construction of well-defined and stable supramolecular architectures with chemical functionalities and physical properties as advanced materials for biological applications.     

On the road to a termolecular complex with acetone: a heterometallic supramolecular network [[Rh(2)(O(2)CCF(3))(4)].micro(2)-OCMe(2).[Cu(4)(O(2)CCF(3))(4)]

A novel heterometallic supramolecular network [[Rh(2)(O(2)CCF(3))(4)].micro(2)-OCMe(2).[Cu(4)(O(2)CCF(3))(4)]](2)( infinity ) has been prepared by codeposition of the volatile mono(acetone) adduct [Rh(2)(O(2)CCF(3))(4).eta(1)-OCMe(2)](2) and copper(I) trifluoroacetate, [Cu(4)(O(2)CCF(3))(4)]. The product is of interest from the viewpoints of gas-phase supramolecular synthesis and a rare bridging coordination mode of acetone. It has been fully characterized by IR and NMR spectroscopy, elemental analysis, and X-ray diffraction. An X-ray structure revealed a layered 2D arrangement of the heterometallic [[Rh(2)(O(2)CCF(3))(4)].micro(2)-OCMe(2).[Cu(4)(O(2)CCF(3))(4)]] units built by axial intermolecular interactions of the open electrophilic Rh(II) and Cu(I) centers and O-atoms of neighboring carboxylate groups. The coordination of the acetone molecules within the [[Rh(2)(O(2)CCF(3))(4)].micro(2)-OCMe(2).[Cu(4)(O(2)CCF(3))(4)]] unit is asymmetric with the Rh-O and Cu-O distances being 2.2173(15) and 2.7197(17) A, respectively. This work shows the potential of gas-phase deposition that may provide additional possibilities in supramolecular synthesis by utilizing intermolecular interactions and coordination bonds in a new way compared with conventional solution chemistry.     

Metal-mediated self-assembly of protein superstructures: influence of secondary interactions on protein oligomerization and aggregation

We have previously demonstrated that non-self-associating protein building blocks can oligomerize to form discrete supramolecular assemblies under the control of metal coordination. We show here that secondary interactions (salt bridges and hydrogen bonds) can be critical in guiding the metal-induced self-assembly of proteins. Crystallographic and hydrodynamic measurements on appropriately engineered cytochrome cb562 variants pinpoint the importance of a single salt-bridging arginine side chain in determining whether the protein monomers form a discrete Zn-induced tetrameric complex or heterogeneous aggregates. The combined ability to direct PPIs through metal coordination and secondary interactions should provide the specificity required for the construction of complex protein superstructures and the selective control of cellular processes that involve protein-protein association reactions.     

Tetraalkoxyaluminates of nickel(II), copper(II), and copper(I)

The syntheses and structural details of tetraisopropoxyaluminates and tetra-tert-butoxyaluminates of nickel(II), copper(I), and copper(II) are reported. Within the nickel series, either Ni[Al(OiPr)4]2.2HOiPr, with nickel(II) in a distorted octahedral oxygen environment, or Ni[Al(OiPr)4]2.py, with nickel(II) in a square-pyramidal O4N coordination sphere, or Ni[(iPrO)(tBuO)3Al]2, with Ni(II) in a quasi-tetrahedral oxygen coordination, has been obtained. Another isolated complex is Ni[(iPrO)3AlOAl(OiPr)3].3py (with nickel(II) being sixfold-coordinated), which may also be described as a "NiO" species trapped by two Al(OiPr)3 Lewis acid-base systems stabilized at nickel by three pyridine donors. Copper(I) compounds have been isolated in three forms: [(iPrO)4Al]Cu.2py, [(tBuO)4Al]Cu.2py, and Cu2[(tBuO)4Al]2. In all of these compounds, the aluminate moiety behaves as a bidentate unit, creating a tetrahedrally distorted N2O2 copper environment in the pyridine adducts. In the base-free copper(I) tert-butoxyaluminate, a dicopper dumbbell [Cu-Cu 2.687(1) A] is present with two oxygen contacts on each of the copper atoms. Copper(II) alkoxyaluminates have been characterized either as Cu[(tBuO)4Al]2, {Cu(iPrO)[(iPrO)4Al]}2, and Cu[(tBuO)3(iPrO)Al]2 (copper being tetracoordinated by oxygen) or as [(iPrO)4Al]2Cu.py (pentacoordinated copper similar to the nickel derivative). Finally, a copper(II) hydroxyaluminate has been isolated, displaying pentacoordinate copper (O4N coordination sphere) by dimerization, with the formula {[(tBuO)4Al]Cu(OH).py}2. The formation of all of these isolated products is not always straightforward because some of these compounds in solution are subject to decomposition or are involved in equilibria. Besides NMR [copper(I) compounds], UV absorptions and magnetic moments are used to characterize the compounds.