Molecular tectonics on surfaces: Bottom-up fabrication of 1D coordination networks that form 1D and 2D arrays on graphite.
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Crystallography, X-Ray↗
Biomedical subjects
Nathalie Kyritsakas
Publications and source records attributed to Nathalie Kyritsakas.
Solid-state self-assembly of polymeric double helicates leading to linear arrays of silver(I) ions and reversible strand/double helix interconversion in solution.
Reaction of a bent py-hyz-pym-hyz-pym 1 and of a linear py-hyz-py-hyz-pym 3 (py=pyridine; pym=pyrimidine; hyz=hydrazone) ligand strands with silver(I) tetrafluoroborate in CH(3)NO(2) generates double-helical dinuclear 2 and trinuclear 4 complexes. These complexes form polymeric, highly ordered solid-state structures, with wirelike, linear continuous or discontinuous polycationic Ag(n) (+) arrays with Ag--Ag distances of 2.78 to 4.42 A. Ligand 5, an isomer of 1, is found to yield a [2x2] grid-type complex 6. Titration experiments reveal the formation of linear rack-type dinuclear species from 1 and 5. Acid-base modulated, reversible interconversion between strand 1 and double helicate 2 may be achieved by using tren as a competing complexing agent (tren=N(CH(2)CH(2)NH(2))(3)). Progressive addition of silver(I) ions to a 1:1 mixture of 1 and 5 leads to the preferential formation of the double helicate 2 over the grid complex 6, illustrating a process of self-organisation with selection of the correct ligand.
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Arranging up to six ferrocene carboxamides around metal centres.
Ferrocene carboxamide, FcCONH(2), forms homo- and heteroleptic complexes with Co(II), Ni(II) and Cu(II) via coordination of its carbonyl group. Whereas for both Co(II) and Ni(II), hexaferrocenyl complexes are obtained in the presence of BF(4)(-) anion, in the case of Cu(II) a tetraferrocenyl species is observed in the presence of triflate anion.
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Orthogonal packing of enantiomerically pure helical silver coordination networks.
The combination of the chiral tecton based on the (R)-6,6'-dibromo-1,1'-binaphthyl moiety bearing two isonicotinoyl groups with AgX (X = BF4-, CF3SO3-, PF6-) leads to the formation of enantiomerically pure helical strands with orthogonal packing in the rare space group I2(1)3.
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Formation of RACK- and grid-type metallosupramolecular architectures and generation of molecular motion by reversible uncoiling of helical ligand strands.
The interaction of appropriate metal ions (Pb(II), Zn(II)) with helical ligand strands, obtained by hydrazone polycondensation, generates polymetallic supramolecular architectures of rack and grid types, by uncoiling of the ligand. The interconversion between the helical free ligand and the linearly extended ligand in the complexes produces reversible ion-induced, nanomechanical molecular motions of large amplitude. It has been integrated in an acid-base neutralisation fuelled process, which links the extension/contraction of the ligand strands to alternating changes in pH.
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Ion-triggered multistate molecular switching device based on regioselective coordination-controlled ion binding.
Molecular devices capable of accessing different controlled conformational states, while optically signaling the occupied state, are attractive tools for nanotechnology since they relate to both areas of molecular mechanical devices and logic gates. We report here a simple molecular system that allows access to four distinct conformational and optical states. It is based on the regioselective complexation of metal ions to a heterocyclic ligand triad, which is dictated by the accessible coordination geometry and electrostatic properties of two distinct binding subunits. Thus, local conformational switching is brought about by tetrahedral coordination (of Cu(I)) or octahedral coordination (of M(2+) ions) to bidentate and tridentate binding subunits, respectively. The shape modifications undergone represent an ion-controlled nanomechanical device. They give controlled access to four different states that display different physico-chemical (e.g. optical) properties and provide a basis for logic gate operations.
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Synthesis, structural features, absorption spectra, redox behaviour and luminescence properties of ruthenium(ii) rack-type dinuclear complexes with ditopic, hydrazone-based ligands.
The isomeric bis(tridentate) hydrazone ligand strands 1 a-c react with [Ru(terpy)Cl3] (terpy=2,2':6',2''-terpyridine) to give dinuclear rack-type compounds 2 a-c, which were characterised by several techniques, including X-ray crystallography and NMR methods. The absorption spectra, redox behaviour and luminescence properties (both in fluid solution at room temperature and in rigid matrix at 77 K) of the ligand strands 1 a-c and of the metal complexes 2 a-c have been studied. Compounds 1 a-c exhibit absorption spectra dominated by intense pi-pi* bands, which, in the case of 1 b and 1 c, extend within the visible region, while the absorption spectra of the rack-type complexes 2 a-c show intense bands both the in the UV region, due to spin-allowed ligand-centred (LC) transitions, and in the visible, due to spin-allowed metal-to-ligand charge-transfer (MLCT) transitions. The energy position of these bands strongly depends on the ligand strand: in the case of 2 a, the lowest energy MLCT band is around 470 nm, while in 2 b and 2 c, it lies beyond 600 nm. Ligands 1 a-c undergo oxidation processes that involve orbitals based mainly on the CH3--N--N== fragments. The complexes 2 a-c undergo reversible metal-centred oxidation, while reductions involve the hydrazone-based ligands: in 2 b and 2 c, the bridging ligand is reduced twice and in 2 a once before reduction of the peripheral terpy ligands takes place. Ligands 1 a-c exhibit luminescence from the lowest-lying 1pi-pi* level. Only for complex 2 a does emission occur; this may be attributed to a 3MLCT state involving the bridging ligand. Taken together, the results clearly indicate that the structural variations introduced translate into interesting differences in the spectroscopic, luminescence and redox properties of the ligand strands as well as of the rack-type metal complexes.
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Mixed-valence, mixed-spin-state, and heterometallic [2x2] grid-type arrays based on heteroditopic hydrazone ligands: synthesis and electrochemical features.
An extended family of heterometallic [(M1)2(M2)2(L-)4](n+) [2x2] grid-type arrays 1-9 has been prepared. The three-tiered synthetic route encompasses regioselective, redox and enantioselective features and is based on the stepwise construction of heteroditopic hydrazone ligands A-C. These ligands contain ionisable NH and nonionisable NMe hydrazone units, which allows the metal redox properties to be controlled according to the charge on the ligand binding pocket. The 2-pyrimidine (R) and 6-pyridine (R') substituents have a significant effect on complex geometry and influence both the electrochemical and magnetic behaviour of the system. 1H NMR spectroscopic studies show that the Fe(II) ions in the grid can be low spin, high spin or spin crossover depending on the steric effect of substituents R and R'. This steric effect has been manipulated to construct an unusual array possessing two low-spin and two spin-crossover Fe(II) centres (grid 8). Electrochemical studies were performed for the grid-type arrays 1-9 and their respective mononuclear precursor complexes 10-13. The grids function as electron reservoirs and display up to eight monoelectronic, reversible reduction steps. These processes generally occur in pairs and are assigned to ligand-based reductions and to the Co(III)/Co(II) redox couple. Individual metal ions in the heterometallic grid motif can be selectively addressed electrochemically (e.g., either the Co(III) or Fe(II) ions can be targeted in grids 2 and 5). The Fe(II) oxidation potential is governed by the charge on the ligand binding unit, rather than the spin state, thus permitting facile electrochemical discrimination between the two types of Fe(II) centre in 7 or in 8. Such multistable heterometallic [2x2] gridlike arrays are of great interest for future supramolecular devices incorporating multilevel redox activity.
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Alkoxo-bridged copperII complexes as nodes in designing solid-state architectures. The interplay of coordinative and d10-d10 metal-metal interactions in sustaining supramolecular solid-state architectures.
Four novel polymeric coordination networks have been obtained through self-assembly processes involving alkoxo-bridged copperII species as nodes, and anionic cyano-complexes as linkers: infinity2[{Cu2(pa)2}{M(CN)2}2](M=Ag, 1; Au, 2), (infinity)3[{Cu4(mea)4}{Au(CN)2}4.H2O]3, and (infinity)3[{Cu2(pa)2}{Ni(CN)4}](pa = deprotonated propanolamine; mea = deprotonated monoethanolamine). The supramolecular architectures of compounds 1, and 2 are sustained by argentophilic or strong aurophilic interactions. The solid-state architectures of 1 and 2, which are isomorphous, consist of infinite layers, constructed from binuclear alkoxo-bridged nodes and [M(CN)2]- spacers. The layers are stacked in an offset parallel mode, and are further interconnected through Ag...Ag or Au...Au contacts (1: Ag...Ag 3.015 A; 2: Au....Au 3.069 A). Compound 3 consists of unique fourfold interpenetrating diamondoid nets. The diamondoid topology is built of heterocubane {Cu4O4} nodes, which are connected by [Au(CN)2]- rods. The Cu-O distances within the {Cu4O4} node vary between 1.927(2) and 2.679(1) A, showing unsymmetric bridging of the copper atoms. Aurophilic interactions are established between the bridging and terminal [Au(CN)2]- metalloligands, and connect the interpenetrating nets, resulting in infinite chains of gold atoms (the Au...Au distances vary between 3.253 and 3.305 [Angstrom]). Compound 4 exhibits a 3-D network constructed from {Cu2(pa)2]2+ nodes connected by square-planar [Ni(CN)4]2- ions. Compounds 1, 2 and 4 are weakly paramagnetic. The cryomagnetic investigation of reveals a gradual increase, followed by a decrease of the chiMT product, as the temperature is lowered. A superposition of ferro- (J1=+20.8 cm(-1)) and antiferromagnetic (J2=-6.4) interactions within the tetranuclear node was found. Antiferromagnetic interactions are established between the tetranuclear nodes (theta=-2.99 K).
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Reversible folding/unfolding of linear molecular strands into helical channel-like complexes upon proton-modulated binding and release of metal ions.
The binding of appropriate metal ions to linear ligand strands obtained by hydrazone polycondensations generates channel-like complexes by reversible coiling of the ligand, thus allowing the generation of ion-induced, acid-base neutralisation fueled, molecular nanomechanical contraction/extension motions of large amplitude.
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Dynamic chemical devices: modulation of photophysical properties by reversible, ion-triggered, and proton-fuelled nanomechanical shape-flipping molecular motions.
The terpy-derived (terpy=terpyridine) ligand 1 has an extended W shape in which the two appended photoactive pyrenyl groups are held apart. On binding of a zinc(II) ion with a terpy group, ligand 1 is converted into complex 2 whereby it adopts a U shape, thus stacking the aromatic units. This structural modification leads to a very pronounced change in photophysical properties: from a highly fluorescent free ligand to a very weakly emitting complex. The W/U structural switching can be reversibly induced by the addition of a competitive tren ligand, which binds and releases a zinc(II) ion under protonation/deprotonation cycles, thus leading to oscillations in light emission. Therefore, the present system performs periodic modulation of optical output through a nanomechanical shape-flipping motion, triggered by metal ion binding and fuelled by acid-base neutralisation energy. Overall, it represents an ion-triggered opto-mechanical supramolecular device.
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Dynamic devices. Shape switching and substrate binding in ion-controlled nanomechanical molecular tweezers.
As examples of supramolecular devices performing chemical (ionic, molecular) control of binding events and models of related natural systems, two molecular conformational switches are described, which display cation-controlled nanomechanical motion coupled to substrate binding and release. The substrate binding relies on donor/acceptor interactions, provided by intercalation between planar sites located at the extremities of the switching units, whereas cation complexation is responsible for conformational regulation. The terpyridine py-py-py-based receptor is activated toward substrate binding upon complexation of a zinc(II) cation and operates in a two-state process. The replacement of the central pyridine by a 4,6-disubstituted pyridimine as in py-pym-py induces a state reversal and yields a new receptor which binds a substrate in the absence of cation, and releases it when copper(I) is introduced, following a three-step process. These systems represent effector-triggered supramolecular switching devices leading toward multistate nanomechanical chemical systems. These two systems illustrate the use of simple conformational switches in the binding site and allosteric regulation of substrate affinity.
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Contraction/extension molecular motion by protonation/deprotonation induced structural switching of pyridine derived oligoamides.
NMR, mass spectrometry and X-ray diffraction studies show reversible structural interconversion between helical and extended forms of pyridine derived oligoamide molecular strands, by simple protonation/deprotonation.
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Preparation of six isomeric bis-acylporphyrins with chromophores reaching the near-infrared via intramolecular Friedel-Crafts reaction.
We describe the preparation of six diketones based on the frameworks of five bis-naphthoporphyrins and one perinaphthoporphyrin. All diketones derive from meso-tetraarylporphyrins having incorporated two carbonyl groups, each one connected to one beta-pyrrole carbon and one ortho carbon atom from a meso-aryl group. These compounds were all produced in good yield by intramolecular Friedel-Crafts acylation, either from porphyrins meso-substituted by o-carboxyphenyl or o,o'-dicarboxyphenyl substituents or from porphyrins bearing carboxy groups attached to the pyrrolic beta-positions. Although the former reaction does not show significant regioselectivity when run on nickel complexes, the opposite is true for the corresponding free bases. All diketones show a spectacular bathochromic shift of the UV-vis absorption, the longest wavelength bands absorbing in the 700-825 nm range. Two compounds were structurally characterized by X-ray diffraction. In the case of the diketone, whose carbonyl groups are attached to vicinal pyrrolic beta-positions, a significant intermolecular interaction between the two carbonyl groups and an aromatic hydrogen atom was detected.
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Structural codons: linearity/helicity interconversion by pyridine/pyrimidine exchange in molecular strands.
Pyridine and pyrimidine groups connected through amide functions can be combined into specific sequences that self-organize into either helical or linear structures enforced by the formation of intramolecular hydrogen bonds.
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Charge assisted chiral hybrid H-bonded molecular networks.
The co-crystallisation of [Fe(CN)5NO]2- and cyclic achiral 1(2+) and chiral 2(2+) or 3(2+) bisamidinium tectons leads in the crystalline phase to the formation of 1-D H-bonded achiral and chiral molecular networks respectively. In all cases, the network is formed by mutual bridging of the anionic and cationic units through a chelate mode of H-bonding.
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Synthesis and structural studies of binuclear platinum(II) complexes with a novel phosphorus-nitrogen-phosphorus ligand.
The new pyridinediphosphinite ligand PONOP (1) was synthesized in one step from 2,6-pyridinedimethanol and diphenylchlorophosphane. Reaction of 1 with PtCl(2)(PhCN)(2) led to the neutral homobimetallic complex [Pt(2)Cl(4)(PONOP)(2)] (2), where the benzonitriles have been substituted by the phosphorus atoms of 1. The X-ray structure of 2 revealed a metallamacrocycle where the pyridines remained free. Addition of 2 equiv of [Cu(MeCN)(4)](BF(4)) to 2 led to CuCl and to the binuclear dicationic complex [Pt(2)Cl(2)(PONOP)(2)](BF(4))(2) (3), where chloro ligands have been substituted by pyridine groups. Conversely, reaction of 3 with chloride anions gave back complex 2. Solid-state (X-ray) and solution (NMR) studies indicated that after the transformation of 2 into 3, the platinum centers were brought much closer and the pyridinediphosphinite ligand was stiffened. The methylene NMR protons of 3 were strongly deshielded, and the corresponding proton-phosphorus coupling constants followed a Karplus-type relationship.
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Molecular tectonics: infinite cationic double stranded helical coordination networks.
Upon crystallisation of two bismonodentate tectons based on two pyridine units, interconnected at the meta position by a tetra- or hexa-ethylene glycol fragment and Ag+ cation, double stranded helical infinite coordination networks were formed and structurally characterised. The cationic double helical architectures obtained may be regarded as analogues of DNA in terms of topology.
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