Self-assembly of a heteroduplex helicate from two different ligand strands and Cu(II) cations

CO2 Fixation by Copper(II) Complexes of a Terpyridinophane Aza Receptor

CO2 is fixed by a Cu2+ complex of a macrocyclic terpyridinophane ligand forming a carbamate group. Several features of the structure mimic the enzyme rubisco.

Heterotopic Assemblage of Two Different Disk-Shaped Ligands through Trinuclear Silver(I) Complexation: Ligand Exchange-Driven Molecular Motion

The sandwich-shaped heterotopic trinuclear Ag+ complex Ag(3)1.2 was exclusively formed from two different tris(thiazolyl) and hexa(thiazolyl) disk-shaped ligands, 1 and 2, with the aid of three Ag+ ions. The variable-temperature 1H NMR study on its complexation behavior revealed that metal-ligand exchanges between the two neighboring thiazolyl nitrogen donors of 2 take place at the three Ag+ centers in concert. DeltaH++ and DeltaS++ for the exchange process were calculated to be 50.5 kJ mol(-1) and -26.7 J mol(-1) K(-1), respectively, and its energy barrier at 298 K was estimated to be 58.5 kJ mol(-1). Each concerted metal-ligand exchange leads to an intramolecular 60 degrees-rotational motion ((P) <==>(M) conversion) between the two disk-shaped ligands.

Influence of the coordination geometry on the physicochemical properties of a copper(ii) complex with a tailor-made calixarene-based ligand bearing dipyridyl pendants. An ESR, UV-Vis and CV study

Dipyridyl pendants, suitably attached onto a calix[4]arene fixed in its 1,3-alternate conformation, form stable complexes with copper(ii) in acetonitrile. Both the mononuclear and the homobinuclear species ([Cu(1)](2+) and [Cu(2)(1)](4+)), previously detected through a UV-Vis investigation, have been studied by ESR, UV-Vis and cyclic voltammetry. ESR and UV-Vis data clearly indicate that in the [Cu(1)](2+) species the nitrogen atoms of dipyridyl pendants are tetrahedrally arranged around copper(II). Computer models, optimised through molecular mechanics methods, further support these spectroscopic findings. The tetrahedral arrangement, achieved thanks to the anchoring of the dipyridyl moieties onto the calixarene platform, accounts for the easy reversible reduction of this species. The aspects associated with the reduction-oxidation of the homobinuclear species are also discussed.

Zinc(II)-templated synthesis of a [2]-catenane consisting of a 2,2',6',2' '-terpyridine-incorporating cycle and a 1,10-phenanthroline-containing ring

A nonsymmetrical [2]-catenane has been synthesized, with a 5-coordinated metal center (Zn(2+)) as template. One of the two rings contains a terdentate ligand (2,2',6',2' '-terpyridine) and the other one incorporates a bidentate chelate (1,10-phenanthroline). The first ring was prepared separately and, subsequently, Zn(2+) was used as the gathering and threading element to pass the stringlike component through the ring. This open-chain species bears two terminal olefins, which were reacted with Grubbs first-generation catalyst (ring-closing metathesis) to afford the desired catenane. Hydrogenation of the double bond and removal of the zinc(II) template afforded the final free [2]-catenane in 40% yield from the terdentate ligand-containing cycle and the diolefinic compound. Complexation studies on this new pentacoordinating catenane were carried out with Fe(II) or Cu(II). The most interesting observation is that the 5-coordinated complexes obtained are strongly stabilized. Their electrochemical reduction occurs at negative potentials.

Chiral self-discrimination in a M3L2 subphthalocyanine cage

A tris(3-pyridyl)-substituted C3 symmetric subphthalocyanine (SubPc) was dimerized into a M3L2 cage in the presence of a stoichiometric amount of (en)Pd(NO3)2. NMR studies demonstrated the recognition event to be accompanied by chiral self-discrimination between the two enantiomers of the SubPc. Moreover, the specificity is such that only one of four possible isomers was detected in solution.

Interconversion of a monomer and two coordination polymers of a copper(II)-reduced Schiff base ligand-1,10-phenanthroline complex based on hydrogen- and coordinative-bonding

Two compounds, [Cu(3)(Sbal)(2)(phen)(H(2)O)(2)](ClO(4))(2)-3H(2)O (1) and [Cu(H(2)Sbal)(2)(phen)](ClO(4))(2) (2), were isolated in successive steps from the reaction mixture containing Cu(ClO(4))(2)-6H(2)O, 1,10-phenanthroline, N-(2-hydroxybenzyl)-beta-alanine (H(2)Sbal), and LiOH in the ratio of 1:1:1:1. When the ratio of the base was doubled, the neutral monomer [Cu(Sbal)(phen)]-2H(2)O (3) was obtained. The cation in 1 exists as a one-dimensional polymer in the solid state, while weak O--H...O hydrogen bonds in the cation of 2 generate Delta Lambda Delta Lambda. type one-dimensional spiral chains. Addition of HClO(4) to 3 furnished 1 and 2, and this mixture can be converted back to 3 by the addition of a base. This conversion of a monomer to two 1-D polymers was found to be reversible. Crystal data for 1: triclinic space group P one macro, a = 12.0353(5) A, b = 12.2848(5) A, c = 15.3185(6) A, alpha = 84.993(1) degrees, beta = 89.411(1) degrees, gamma = 67.414(1) degrees, V = 2082.5(2) A(3), Z = 2, rho(calcd) = 1.668 g cm(-3). Crystal data for 2: tetragonal space group P4(1)/a, a = 10.8095(1) A, c = 59.0159(4) A, V = 6895.7(1) A(3), Z = 8, rho(calcd) = 1.605 g cm(-3). Crystal data for 3: monoclinic space group Pn, a = 10.6344(3) A, b = 5.3953(1) A, c = 18.1983(1) A, V = 1029.26(4) A(3), Z = 2, rho(calcd) = 1.526 g cm(-3). When Cu(NO(3))(2) was used in the place of Cu(ClO(4))(2), [Cu(2)(Sbal)(phen)(3)](NO(3))(2)-2.5H(2)O (4) was the only isolable product for the 1:1:1:1 ratio, and 3 was the only isolable product for the 1:1:1:2 ratio. Crystal data for 4: triclinic space group P one macro, a = 10.8063(8) A, b = 13.919(1) A, c = 16.564(1) A, alpha = 88.957(2) degrees, beta = 71.008(1) degrees, gamma = 69.829(2) degrees, V = 2198.9(3) A(3), Z = 2, rho(calcd) = 1.556 g cm(-3). Variable temperature magnetic measurements showed that the polymeric structure in 1 behaves, magnetically, as a strongly coupled micro-phenoxo dimer (2J = -390 cm(-1)) plus an isolated monomer.

Self-assembly with postmodification: kinetically stabilized metalla-supramolecular rectangles

Interaction of a predesigned molecular "clip" (4) with rigid dipyridyl bridging ligands, in acetone/water mixtures, leads to the formation of molecular rectangles (5-8) in 92-97% isolated yields via spontaneous self-assembly. Characterization was accomplished with multinuclear NMR and UV-vis spectroscopy, FAB mass spectrometry, and X-ray crystallography. The length of these metallamacrocycles ranges from 2 to 3 nm. Postmodification via non-nucleophilic counterion exchange results in enhanced structural integrity for the assemblies.

Dominant/recessive behavior in the expression of molecular information: self-assembly of inorganic macrocyclic architectures containing coordinatively unsaturated ligands

The polytopic ligand 1 contains three different metal ion binding subunits forming two substructures that code for the self-assembly of two different coordination structures (helicate and grid type) under metal ion complexation. Reaction with Cu(II) and Zn(II) ions generates the coordinatively unsaturated architectures 8 and 9 resulting from the formation of two double helicate arrangements. Their crystal structure has been determined by x-ray diffraction. These results show that the double helical motif is expressed at the expense of the grid type one, indicating the dominant/recessive behavior of the system. Together with earlier studies on the linear combination and crossover processing schemes, the dominant/recessive generation of 8 and 9 completes the demonstration of principle of the modes of multiple expression of molecular information in a multicode programmed chemical system.

Adaptive self-assembly: environment-induced formation and reversible switching of polynuclear metallocyclophanes

Ligand 3 has been shown to self-assemble under coordination of copper(II) cations in a 1:1 ratio in acetonitrile to give equilibrating mixtures of a [2 x 2] grid-type tetranuclear structure 1 and a hexanuclear achitecture of hexagonal shape 2. The latter was confirmed by determination of the crystal structure which further indicated that 2 contained acetonitrile molecules and hydroxo groups bound to the copper(II) centers, which are therefore five-coordinate. The structures assigned to 1 and 2 were further supported by the spectral (mass, UV/Vis) data. The self-assembly process is strongly dependent on the conditions of the medium. An increase in concentration in acetronitrile increases the relative amount of hexamer 2, which appears to be the favored entity at the highest concentrations that can be reached before precipitation occurs. On the other hand, in nitromethane only the tetranuclear complex 1 was detected by mass spectrometry. Replacement of nitromethane by acetonitrile and vice versa indicated the reversible switching between a solution containing either 1 alone or an equilibrium mixture of 1 and 2, respectively. In conclusion, the system described presents several remarkable features: 1) self-assembly with substrate binding, 2) dynamic combinatorial structure generation, and 3) environment-induced structural switching amounting in effect to a process of adaptive self-assembly.

Coordination-driven assembly of molecular rectangles via an organometallic "clip"

The combination of linear dipyridyl ligands with a new type of modular building unit, based upon a 1,8-platinum-functionalized anthracene, leads to the self-organization of rectangular frameworks. X-ray crystallography confirms the cyclic structure of the supramolecular cationic complexes. Spectral assignments were provided by 2D NOESY (1)H NMR experiments.

From homoleptic to heteroleptic double stranded Copper(I) helicates: the role of self-recognition in self-assembly processes

The ligands 2,9-bis[(6-methyl-2, 2'-bipyridin-6'-yl)methyleneoxymethylenyl]-1,10-phenanthroline (6), 6' ',6' "-bis[(6-methyl-2, 2'-bipyridin-6'-yl)methyleneoxymethylenyl)]-2' ',2' "-bipyridine (2), 5,5'-bis[(6-methyl-2,2'-bipyridin-6'yl)methyleneoxymethylenyl]-2, 2'-bithiophene (7), and 6,6'-bis[(6-methyl-2, 2'-bipyridin-6'-yl)methyleneoxymethylenyl]-2,2'-biphenyl (8) and their respective homo- and heteroleptic double-stranded copper(I) complexes were prepared and characterized in order to estimate the importance of self-recognition in the self-assembly processes of double-stranded copper complexes. The homoleptic double-stranded copper complexes of 2, 6, 7, and 8 were characterized by NMR, FAB-MS, and electrochemistry. It was found that 6 and 2 each form a single double-stranded helicate having the structure of [(L)(2)Cu(3)](3+) (L = 2 or 6), 7 forms two double-stranded [(7)(2)Cu(3)](3+) complexes, and 8 results in a mixture of at least two [(8)(2)Cu(2)](2+) complexes. The potential shift, DeltaE degrees (,) of the Cu(+)/Cu(2+) redox process of these complexes reflects the binding affinity of the different binding sites to the copper cation. The electrochemical data show that the central units have a higher affinity to Cu(+) as compared to the off-center binding sites. NMR was used to determine the actual complex composition obtained from different mixtures of 2, 6, or 7 with Cu(+). Interestingly, we have found that, although 6, 2, and 7 each form homoleptic double-stranded complexes, no heteroleptic double-stranded copper complexes were formed from the mixtures of 7 with either 6 or 2. However, when mixtures of 6 and 2 are used, helicate distributions seem to follow simple statistics. These results are discussed in terms of the relative importance of self-recognition in the self-assembly of double-stranded helicates.

Electrochemically and Photochemically Driven Ring Motions in a Disymmetrical Copper [2]-Catenate

By applying the three-dimensional template effect of copper(I), previously used for making various interlocking ring systems, a new disymmetrical [2]-catenate has been made which consists of two different interlocking rings. One ring contains a 2,9-diphenyl-1,10-phenanthroline (dpp) unit whereas the other cycle incorporates both a dpp motif and a 2,2',6',2''-terpyridine (terpy) fragment, the coordination site of these two chelates pointing toward the inside of the ring. Depending on the oxidation state of the central metal (Cu(I) or Cu(II)), and thus on its preferred coordination number, two distinct situations have been observed. With monovalent copper, the two dpp units interact with the metal and the terpy fragment remains free, at the outside of the molecule. By contrast, when the catenate is complexed to divalent copper, the terpy motif is bonded to the metal and it is now a dpp ligand which lies at the periphery of the complex. This dual coordination mode leads to dramatically different molecular shapes and properties for both forms. The molecular motion which interconverts the four- and the five-coordinate complexes can be triggered chemically, electrochemically, or photochemically by changing the oxidation state of the copper center (II/I). The process has been studied by electrochemistry and by UV-vis spectroscopy. Interestingly, once the stable 4-coordinate copper(I) complex has been oxidized to a thermodynamically unstable pseudo-tetrahedral copper(II) species, the rate of the gliding motion of the rings which will afford the stable 5-coordinate species (copper(II) coordinated to dpp and terpy) can be controlled at will. Under certain experimental conditions, the changeover process is extremely slow (weeks), and the 4-coordinate complex is more or less frozen. By contrast, addition of a coordinating counterion to the medium (Cl^-) enormously speeds up the rearrangement and leads to the thermodynamically stable 5-coordinate complex within minutes.

Multicomponent Self-Assembly: Generation of Rigid-Rack Multimetallic Pseudorotaxanes

The rigid linear ligands 1a-g and the macrocycle 2 undergo self-assembly via coordination with copper(I) ions to generate the series of rigid-rack inorganic pseudorotaxanes 3a-g. These complexes have been characterized by analytical and spectroscopic methods. Their architecture has been confirmed by determination of the crystal structures of 3e,f. The complex [Cu(2)(1e)(2)(2)](PF(6))(2) (3e) crystallizes in the space group C2/c, whereas complex [Cu(2)(1f)(2)(2)](PF(6))(2) (3f) gives crystals containing a single enantiomer in the chiral space group P2(1)2(1)2(1). The synthesis and solution structures of 3a-g and the solid-state structures of 3e,f are discussed in relation to the viability of multicomponent self-assembly as an approach to linear metal-ion arrays.