Aurélien Crochet

Polymorphism, what it is and how to identify it: a systematic review

This review on polymorphism is a personal, non-comprehensive view on the field of polymorphism – a term which is often misused. Indeed, the discussion about polymorphism and related terms is still ongoing in the area of crystal engineering. This is why we felt it timely to look into the historical development of its definition and to delimit it. A short introduction to thermodynamic aspects and characterization methods of polymorphs is given. One chapter is then dedicated to polymorphism of elements and inorganic compounds, before discussing the term for organic and organo-metallic compounds. Chosen examples are given each time to illustrate the cases of polymorphism. In the end, the conclusion yields three flow schemes useful in determining polymorphism for each compound class.

Synthesis, X-ray structure and in vitro cytotoxicity studies of Cu(I/II) complexes of thiosemicarbazone: special emphasis on their interactions with DNA.

4-(p-X-phenyl)thiosemicarbazone of napthaldehyde {where X = Cl (HL¹) and X = Br (HL²)}, thiosemicarbazone of quinoline-2-carbaldehyde (HL³) and 4-(p-fluorophenyl)thiosemicarbazone of salicylaldehyde (H₂L⁴) and their copper(I) {[Cu(HL¹)(PPh₃)₂Br]·CH₃CN (1) and [Cu(HL²)(PPh₃)₂Cl]·DMSO (2)} and copper(II) {[(Cu₂L³₂Cl)₂(μ-Cl)₂]·2H₂O (3) and [Cu(L⁴)(Py)] (4)} complexes are reported herein. The synthesized ligands and their copper complexes were successfully characterized by elemental analysis, cyclic voltammetry, NMR, ESI-MS, IR and UV-Vis spectroscopy. Molecular structures of all the Cu(I) and Cu(II) complexes have been determined by X-ray crystallography. All the complexes (1-4) were tested for their ability to exhibit DNA-binding and -cleavage activity. The complexes effectively interact with CT-DNA possibly by groove binding mode, with binding constants ranging from 10⁴ to 10⁵ M⁻¹. Among the complexes, 3 shows the highest chemical (60%) as well as photo-induced (80%) DNA cleavage activity against pUC19 DNA. Finally, the in vitro antiproliferative activity of all the complexes was assayed against the HeLa cell line. Some of the complexes have proved to be as active as the clinical referred drugs, and the greater potency of 3 may be correlated with its aqueous solubility and the presence of the quinonoidal group in the thiosemicarbazone ligand coordinated to the metal.

A Thermo- and Mechanoresponsive Cyano-Substituted Oligo(p-phenylene vinylene) Derivative with Five Emissive States.

Multiresponsive materials that display predefined photoluminescence color changes upon exposure to different stimuli are attractive candidates for advanced sensing schemes. Herein, we report a cyano-substituted oligo(p-phenylene vinylene) (cyano-OPV) derivative that forms five different solvent-free solid-state molecular assemblies, luminescence properties of which change upon thermal and mechanical stimulation. Single-crystal X-ray structural analysis suggested that tolyl groups introduced at the termini of solubilizing side-chains of the cyano-OPV play a pivotal role in its solid-state arrangement. Viewed more broadly, this report shows that the introduction of competing intermolecular interactions into excimer-forming chromophores is a promising design strategy for multicolored thermo- and mechanoresponsive luminescent materials.

Kinetics of Ion Transport through Supramolecular Channels in Single Crystals

Single-crystal to single-crystal transformations are possible by ion-exchange and transport reactions through supramolecular channels that are composed of crown ether molecules and use trihalide ions as scaffolds. Kinetic measurements of ion transport at different temperatures provide activation energy data and show that a very fast exchange of K(+) ions with Na(+) ions occurs.

Greasy tails switch 1D-coordination [{Zn2(OAc)4(4′-(4-ROC6H4)-4,2′:6′,4′′-tpy)}n] polymers to discrete [Zn2(OAc)4(4′-(4-ROC6H4)-4,2′:6′,4′′-tpy)2] complexes

The homologous series of 4′-(4-ROC6H4)-4,2′:6′,4′′-tpy ligands with R = Me, Et, nPr, nBu, npentyl, nhexyl, nheptyl, noctyl, nnonyl and ndecyl (1–10, respectively) are reported, including single crystal structures of 6 and 7. Reactions of zinc(II) acetate with 1–10 have been investigated using room temperature crystallization methods (diffusion or layering). For ligands with the shortest alkoxy substituents, 1-dimensional coordination polymers [{Zn2(OAc)4(L)}n] (L = 1, 2 or 3) are formed. In each polymer, the 4′-(4-ROC6H4)-4,2′:6′,4′′-tpy ligands bind zinc through the two outer pyridine donors. The polymer structures are similar with the n-propyl chain adopting a folded conformation in [{Zn2(OAc)4(3)}n] which allows it to fit in the cavity occupied by methyl or ethyl groups in [{Zn2(OAc)4(1)}n] and [{Zn2(OAc)4(2)}n]. Reaction between 5 and Zn(OAc)2·2H2O gives both the coordination polymer [{2Zn2(OAc)4(5)·2H2O}n] and the discrete complex [Zn2(OAc)4(5)2]. Although the zig-zag form of the polymer chain in [{2Zn2(OAc)4(5)·2H2O}n] mimics those in [{Zn2(OAc)4(L)}n] (L = 1, 2 or 3), packing interactions differ and the wider separation of the chains in a sheet results in the incorporation of water molecules in the lattice. π-Stacking between pyridine rings in [{Zn2(OAc)4(L)}n] (L = 1, 2 or 3) produces infinite assemblies in contrast to isolated tetradecker π-stacks in [{2Zn2(OAc)4(5)·2H2O}n]. This assembly is replicated in [{4Zn2(OAc)4(7)·3H2O}n] (n-heptoxy substituents). In contrast, the n-hexoxy-containing coordination polymer crystallizes with acetic acid in the lattice; [{Zn2(OAc)4(6)·MeCO2H}n] consists of zig-zag polymer chains which π-stack in a manner which is unique among the other polymers. Further lengthening of the alkoxy chain favours the formation of [Zn2(OAc)4(L)2] (L = 8, 9 or 10) which are analogues of [Zn2(OAc)4(5)2]. In each, the 4′-(4-ROC6H4)-4,2′:6′,4′′-tpy ligand is monodentate. The alkoxy chains are in extended (or close to extended) conformations and pack into planar sheets with interdigitated chains. Pockets in the sheets are occupied by methyl groups of {Zn2(OAc)4} units in the adjacent sheet in a ball-and-socket assembly motif. The study shows that coordination polymers [{Zn2(OAc)4(L)}n] in which π-stacking are the dominant interactions are favoured for small alkoxy substituents (ligands 1–3); for ligands 8–10, discrete complexes [Zn2(OAc)4(L)2] in which van der Waals interactions dominate are observed. In the intermediate range (ligands 5–7), the preference between the two structure types appears to be marginal.

Do perfluoroarene⋯arene and C–H⋯F interactions make a difference to the structures of 4,2′:6′,4′′-terpyridine-based coordination polymers?

The consequences for the structures of coordination polymers of introducing fluoro substituents into the terminal phenyl domain of 4′-(biphenyl-4-yl)-4,2′:6′,4′′-terpyridine (1) have been investigated. Reaction between Cu(OAc)2·H2O and 4′-(2′,3′,4′,5′,6′-pentafluorobiphenyl-4-yl)-4,2′:6′,4′′-terpyridine (2) yields the one-dimensional coordination polymer [Cu2(μ-OAc)4(2)]n which contains paddle-wheel {Cu2(OAc)4} nodes bridged by ligands 2. The compound is isostructural with [Cu2(μ-OAc)4(1)]n. When Cu(OAc)2·H2O reacts with a 1:1 mixture of 1 and 2, [Cu2(μ-OAc)4(1)]n and [Cu2(μ-OAc)4(2)]n co-crystallize with 1 and 2 disordered over one ligand site; the one-dimensional coordination polymer is isostructural with each of [Cu2(μ-OAc)4(1)]n and [Cu2(μ-OAc)4(2)]n indicating that replacing H by F substituents in the peripheral arene ring has no effect on the overall solid-state structure: tpy⋯tpy π-stacking is preserved, arene⋯arene πH⋯πH interactions are replaced by perfluoroarene⋯arene πF⋯πH interactions, and H⋯H contacts are replaced by H⋯F interactions. In stark contrast to the latter observations, the reaction of Zn(OAc)2·2H2O with perfluoro derivative 2 yields [Zn5(OAc)10(2)4·11H2O]n as the dominant one-dimensional polymer; minor amounts of the anticipated polymer [Zn2(μ-OAc)4(2)]n are also formed. The solid-state structure of [Zn5(OAc)10(2)4·11H2O]n consists of quadruple-stranded polymer chains assembled from {Zn5(2)4} subchains interconnected by {Zn5(OAc)10} units. Within each chain, πF⋯πF and πH⋯πH stacking interactions are dominant, while the observed assembly of chains into sheets and π-stacking between arene units in adjacent sheets mimic the dominant interactions in the single-stranded chains observed in [Zn2(μ-OAc)4(1)]n, [Zn2(μ-OAc)4(2)]n, [Cu2(μ-OAc)4(1)]n, [Cu2(μ-OAc)4(2)]n and [Cu2(μ-OAc)4(1)]n·[Cu2(μ-OAc)4(2)]n.

Synthesis, X-ray structure and DFT calculation of oxido-vanadium(V) complex with a tridentate Schiff base ligand

Reaction of 4-bromo-2-(((5-chloro-2-hydroxyphenyl) imino)methyl)phenol (H2L) with VOSO4·XH2O generates the oxido-vanadium(V) complex [VOL(OCH3)(OHCH3)], that characterized by FT-IR, UV–Vis, and elemental analysis. The complex was also characterized by single crystal X-ray diffraction crystallography. A DFT calculation was carried out on the complex using the B3LYP/6-31+G(d,p) method. The agreement between the theoretical and experimental data is good. NBO data shows that the donation from donor atoms to the metal center is greater than back bonding.

Controlled tautomerism – switching caused by an “underground” anionic effect

In a previous communication, we demonstrated a conceptual idea for a tautomeric switching system based on implementation of a flexible piperidine unit in 4-(phenyldiazenyl)naphthalen-1-ol (1). The results showed that a directed shift in the position of the tautomeric equilibrium can be achieved through protonation/deprotonation in a number of solvents. However, the effect of the counter ion in the process of protonation was never considered. The crystallographic analysis of protonated cyano and nitro derivatives of 4-(phenyldiazenyl)-2-(piperidin-1-ylmethyl)naphthalen-1-ol have shown an interesting and unexpected feature: the counter ion is captured in the process of protonation and the shift in the position of the tautomeric equilibrium is achieved through a bridged complex formation. To the best of our knowledge this is a rare example when controlled shift in the position of tautomeric equilibrium is achieved through anion complexation. The results from the solid state analyses are confirmed by NMR spectroscopy in solution and by quantum-chemical calculations.

Influence of anions and solvent molecules on the packing and emission spectra of coordination polymers based on silver ions and an anthracene derivative

Luminescence between green and blue was observed in the solid state for the free ligand L (anthracene-9,10-diylbis(methylene) dinicotinate) and five different Ag-L coordination polymers upon excitation at 344 nm. Depending on the packing of the anthracene moieties due to coordinating anions and the presence or absence of solvent molecules, the emission maximum is shifted.

Versatile reactivity and theoretical evaluation of mono- and dinuclear oxidovanadium(V) compounds of aroylazines: electrogeneration of mixed-valence divanadium(IV,V) complexes

The substituted hydrazones H2L(1-4) (L(1-4) = dibasic tridentate ONO(2-) donor ligands) obtained by the condensation of 2-hydroxy-1-naphthaldehyde and 2-aminobenzoylhydrazine (H2hnal-abhz) (H2L(1)) , 2-hydroxy-1-naphthaldehyde and 2-hydroxybenzoylhydrazine (H2hnal-hbhz) (H2L(2)), 2-hydroxy-1-acetonaphthone and benzoylhydrazine (H2han-bhz) (H2L(3)), or 2-hydroxy-1-acetonaphthone and 2-aminobenzoylhydrazine (H2han-abhz) (H2L(4)) are prepared and characterized. Reaction of ammonium vanadate with the appropriate H2L(1-4) results in the formation of oxidoethoxidovanadium(V) [V(V)O(OEt)(L(1-4))] (1-4) complexes. All compounds are characterized in the solid state and in solution by spectroscopic techniques (IR, UV-vis, (1)H, (13)C, and (51)V NMR, and electrospray ionization mass spectrometry). Single-crystal X-ray diffraction analysis of 1, 3, and 4 confirms the coordination of the corresponding ligands in the dianionic (ONO(2-)) enolate tautomeric form. In solution, the structurally characterized [V(V)O(OEt)(L)] compounds transform into the monooxido-bridged divanadium(V,V) [(V(V)OL)2-μ-O] complexes, with the processes being studied by IR and (1)H, (13)C, and (51)V NMR. The density functional theory (DFT) calculated Gibbs free energy of reaction 2[V(V)O(OEt)(L(4))] + H2O ⇆ [(V(V)OL(4))2-μ-O] + 2EtOH is only 2-3 kcal mol(-1), indicating that the dinuclear complexes may form in a significant amount. The electrochemical behavior of the complexes is investigated by cyclic voltammetry, with the V(V)-V(IV) E1/2(red) values being in the range 0.27-0.44 V (vs SCE). Upon controlled potential electrolysis, the corresponding (L)(O)V(IV)-O-V(V)(O)(L) mixed-valence species are obtained upon partial reduction of the [(V(V)OL)2-μ-O] complexes formed in solution, and some spectroscopic characteristics of these dinuclear mixed-valence complexes are investigated using DFT calculations and by electron paramagnetic resonance (EPR), with the formation of V(IV)-O-V(V) species being confirmed by the observation of a 15-line pattern in the EPR spectra at room temperature.