Synthesis, Characterization, and Properties of a Titanium(IV)-Tetrathiafulvalene-Based Complex.

To deeply investigate the interaction between a tetrathiafulvalene (TTF) unit and a Ti(IV) center, a monomeric heteroleptic octahedral Ti(IV) complex containing a diimine ligand composed of a 1,10-phenanthroline core fused with a TTF fragment (ligand 2a) was prepared. The stable complex formulated as Ti(1)2(2a), where 1 is a 2,2'-biphenolato derivative, was efficiently synthesized by following a one-step approach. This complex and its model species [Ti(1)2(2b)] were fully characterized in solution, and their solid-state structures were established by single-crystal X-ray diffraction analysis. Density functional theory calculations allowed the assignment of the frontier orbitals involved in the electronic transitions characterized by ultraviolet-visible absorption spectroscopy. Electrochemical and spectroelectrochemical studies revealed that the TTF unit within Ti(1)2(2a) can undergo two reversible one-electron oxidation processes; a reversible one-electron reduction of the Ti(IV) atom was highlighted. The photophysical measurements performed for this donor-acceptor molecular system indicated that an electron transfer process upon light excitation occurred within Ti(1)2(2a).

Selective gas adsorption by calixarene-based porous octahedral M32 coordination cages.

Giant octahedral M32 coordination cages were prepared via self-assembly of sulfonylcalix[4]arene-supported tetranuclear M(II) clusters (M = Co, Ni) with hybrid linker based on tris(dipyrrinato)cobalt(III) complexes appended with peripherical carboxylic groups. Due to intrinsic and extrinsic porosity, the obtained solid-state supramolecular architectures demonstrated good performance as adsorbents for the separation of industrially important gases mixtures.

Photocycloadditions of Arenes Derived from Lignin.

Intramolecular photocycloaddition reactions of 3,4-alkoxybenzonitriles derived from vanillin with alkenes have been investigated. In contrast to previous reports on photochemical reactions with these compounds, mainly [2 + 3] cycloaddition has been observed. A competing [2 + 2] photocycloaddition plays a minor role. Most probably, these additions occur at the singlet state S1. In the case of a triplet reaction, a different regioselectivity of the [2 + 2] cycloaddition would be observed. Linear and angular [2 + 3] cycloadducts are formed as major products. The first isomer is transformed in the second one by a photochemical vinyl-cyclopropane rearrangement, which increases the selectivity of the reaction. The influence of the substitution pattern on the reactivity and the selectivity has also been investigated.

HKUST-1 MOF in reline deep eutectic solvent: synthesis and phase transformation.

The fate of HKUST-1 (Cu3(BTC)2, BTC = 1,3,5-benzenetricarboxylate) in the green Deep Eutectic Solvent (DES) reline (choline chloride/urea 1 : 2) was investigated, highlighting that not only reline can be used to make this MOF but also to transform it into another crystalline material. The synthesis of HKUST-1(reline) showing good textural properties and a particular rose morphology was indeed successfully achieved in this solvent. However, upon optimizing the reaction conditions such as concentration and metal/ligand ratio, it was found that another structure Cu2(BTC)Cl also forms. It was unequivocally demonstrated that, upon heating in reline, HKUST-1 converts to the non-porous chloride-incorporating material. Hence, a novel feature of DES in MOF synthesis is uncovered: its role as a structure-directing agent, triggering the transformation between two different MOF structures.

Dipyrrin based metal complexes: reactivity and catalysis.

Sometimes named half-porphyrins, bis-pyrrolic dipyrrin ligands endow their metal complexes with unique properties such as the potential to functionalize the heterocyclic backbone or the meso position and the ability to catalyze interesting chemical transformations. Thus, strategies towards the derivatization of or at the meso group and the use of dipyrrin metal complexes for the formation of a broad range of polypyrrolic derivatives such as 2,2'-bis-dipyrrins, nor-/hetero-corroles and porphynoids have been elaborated. Furthermore, the chelating ability of dipyrrins and the possibility of modifying their steric and electronic characteristics by functionalization can be exploited for the development of numerous complexes featuring appealing properties. Hence, C-H activation/amination, polymerization or oxidation reactions can be catalyzed by dipyrrin metal complexes and classical reagents such as Grignard species, Rh-based or Suzuki-Miyaura catalysts have been revisited by incorporation of dipyrrins in the coordination sphere of the metal cations. This contribution aims to review and illustrate all these aspects, highlighting the potential of these complexes for the design and synthesis of valuable organic compounds and metallo-organic architectures.

Interdigitated conducting tetrathiafulvalene-based coordination networks.

Assembly of a novel ethylenedithio-tetrathiafulvalene (EDT-TTF) derivative bearing two adjacent 4-thiopyridyl groups with M(NCS)2 nodes (M = Fe, Co) leads to two isostructural 1D coordination polymers showing an enhancement of their electronic conductivity by six orders of magnitude (10-6vs. 10-12 S cm-1), upon surface oxidation by iodine and subsequent generation of EDT-TTF-based radicals.

Strapping a benzaldehyde-appended 2,2'-bis-dipyrrin Zn(ii) double-stranded helicate using imine bond formation.

A novel linear binuclear Zn(ii)/2,2'-bis-dipyrrin double-stranded helicate bearing peripheral p-benzaldehyde moieties has been strapped by formation of imine bonds upon reaction with m-xylylenediamine and characterized by 1H- and 13C-NMR spectroscopy, UV-Visible spectroscopy and high-resolution mass spectrometry.

Pre-organization of clefts for Ag-π interactions in Zn(ii) bisdipyrrin helicates for the construction of heterometallic networks.

Coordination of 2,2'-bisdipyrrin based ligands to Zn(ii) cations leads to the formation of binuclear helicates with pre-organized pyrrolic strands as well as peripheral aromatic moieties for Ag-π interactions, thus affording crystalline heterometallic networks upon further interactions with Ag(i) salts without the assistance of additional heteroatom-based coordinating units.

On Zn(II) 2,2'-bisdipyrrin circular helicates.

Coordination of two 2,2'-bisdipyrrin ligands, bearing methyl ester or methylthioether peripheral groups, with Zn(II) cations leads not only to the formation of the expected linear helicates but also concomitantly to novel tri- and tetra-nuclear circular species that have been isolated and fully characterized in solution and by X-ray diffraction.

Assembly, disassembly, and reassembly: conversion of homometallic coordination networks into mixed metal-organic frameworks.

A strategy for the conversion of homometallic coordination networks into mixed metal-organic frameworks (MM'MOFs) is proposed. Ni(II) complexes of dipyrrin (dpm) ligands bearing peripheral pyridyl or imidazolyl units have been shown to self-assemble into coordination polymers with the metal cation in an octahedral environment coordinated to two bis-pyrrolic chelates and two neutral monodentate coordinating units such as pyridyl or imidazolyl moieties. Taking advantage of the chelate effect, the two monodentate units may be replaced by a diimine ligand leading to the disassembly of the networks by the formation of discrete soluble complexes. The latter can be employed as metallatectons for the construction of heterometallic architectures upon reaction with a secondary metal salt. This approach was applied using either 1,10-phenanthroline (phen) or 2,2'-bipyrimidine (bpm) as chelates leading to a series of mono- and binuclear metallatectons of the (phen)Ni(dpm)2 and (bpm)[Ni(dpm)2]2 type. Subsequent assembly with CdCl2 afforded either interpenetrated 2D grid-type architectures or 3D MM'MOFs.

A silver bite: crystalline heterometallic architectures based on Ag-π interactions with a bis-dipyrrin zinc helicate.

An unprecedented mode of assembly of helical motives and Ag(I)  ions in the crystalline state is described. The combination of a Zn(II) helicate based on a 2,2'-bisdpm bearing peripheral benzonitrile moieties with AgX salts, leads to the formation of a tetranuclear core containing Ag-π interactions. Depending on the coordinating ability of the X(-) anion and the solvents used, the tetranuclear complex self-assembles into coordination polymers of varying dimensionality. From the sequence of coordination events (Ag-π or Ag-peripheral site), one may envisage two possible construction scenarios. However, the Ag-π as primary event seems reasonable owing to the rather weak binding propensity of the nitrile group and the chelating nature of the π-clefts.

From sequential to one-pot synthesis of dipyrrin based grid-type mixed metal-organic frameworks.

Both sequential and one-pot strategies for the preparation of a series of grid-type mixed metal-organic frameworks (MM'MOFs) based on dipyrrin ligands appended with either a pyridyl or a phenyl-imidazolyl moiety have been investigated. For the stepwise approach, the differentiation between the two coordination sites (nature, charge, and denticity) was exploited for the synthesis of a family of five discrete Zn(II), Cu(II), and Pd(II) complexes. Acting as metallatectons, these construction building blocks lead to the formation of a series of MM'MOFs upon self-assembly with CdCl2. In these rhombic grid-type architectures, four consecutive metallatectons are bridged by Cd(II) cations adopting an octahedral coordination geometry with the chloride anions occupying apical positions, thus behaving as square nodes. The shape of the rhombus grids as well as the way they are packed (stacking or interpenetration) in the crystalline phase are controlled by the nature of metallatectons and the solvent molecules present in the crystals. Consequently, the heterometallic assemblies display different accessible voids, although they are built on layers with the same connectivity. More interestingly, as demonstrated by X-ray diffraction on both single crystals and microcrystalline powders, the same MM'MOFs were obtained by a one-pot strategy through direct combinations of dipyrrin derivatives with the corresponding metal salts. This one-pot approach is efficient and more convenient than the sequential alternative, since the isolation, purification, and characterization of the, sometimes insoluble, metallatectons are not required.

Luminescent dipyrrin based metal complexes.

While they may have been overshadowed by the brightness of their BODIPY analogues, dipyrrin based metal complexes have recently appeared as novel interesting luminescent species owing to the development of various synthetic strategies for the preparation of such coordination compounds with appreciable quantum yields and tuneable emission wavelength. Not only the rigidification brought by functionalization of the dipyrrin backbone either at position 5 or positions 1 and 9, but also a careful choice of the ligands present in the complex coordination sphere have been key in these developments leading to bright and stable emitters. At position 5, equivalent to the meso position of a porphyrin, introduction of peripheral groups, such as the mesityl moiety hindering the rotational freedom of this unit, has been particularly targeted, hence limiting a favourable non-radiative deactivation pathway. Regarding positions 1 and 9, their proximity to the metal center has prompted their use for the introduction of additional coordinating units, thus providing a pseudo-macrocyclic character to the ligands. In this perspective article, the different types of modification of dipyrrin as well as the resulting metal complexes incorporating these derivatives, their photophysical properties and their applications in sensing and materials science are reviewed.

Luminescent coordination polymers based on self-assembled cadmium dipyrrin complexes.

A series of novel Cd(II) complexes based on α,ß-unsubstituted dipyrrin ligands (dpm) has been prepared and characterised both in solution and in the solid state. These compounds are of the [Cd(dpm)(2)] type, with the coordination sphere of the metal centre occupied by two dpm chelates. Interestingly, in contrast to what has been reported for the Zn(II) analogues, in the presence of a pyridyl- or imidazolyl-appended dpm ligand, the coordination number of the Cd(II) cation can be increased to six, leading to an octahedral coordination sphere. As a consequence, the formation of 1-, 2-, and 3D coordination polymers by self-assembly is observed. Photophysical investigations of the discrete complexes and self-assembled networks have demonstrated that both types of compounds are luminescent in the solid state.

Stepwise construction of grid-type Cu(II)-Cd(II) heterometallic MOFs based on an imidazole-appended dipyrrin ligand.

An imidazole-appended dipyrrin ligand yields, upon coordination to Cu(II) cations, a linear metallatecton that self-assembles with Cd(II) salts to afford 2D grid-type MOFs which, upon parallel stacking, lead to porous crystals offering 1D channels.

Heterometallic coordination polymers incorporating dipyrrin based heteroleptic copper and cobalt complexes: to Ag-π or not?

Using ligands based on either an acetylacetonate or a dipyrrin moiety appended with pyridyl groups, a series of novel heteroleptic copper(II) and cobalt(III) complexes combining both chelate units such as (acacpy(2))Cu(dpm-py) and (acacpy(2))Co(dpm-py)(2) (acacpy(2) = 1,3-bis(4-pyridyl)-1,3-propanedionate; dpm-py = 5-(4-pyridyl)dipyrrin) have been prepared and fully characterized. These two complexes were obtained upon reaction of dpm-py with the (acacpy(2))M homoleptic species (M = Cu(II), Co(II)). In the solid state, the (acacpy(2))Cu(dpm-py) complex behaves as a self-complementary metallatecton and leads to the formation of a 1D coordination polymer (CP) through the coordination of a peripheral pyridyl group to the copper centre. Contrastingly, the octahedral (acacpy(2))Co(dpm-py)(2) complex featuring a coordinatively saturated Co(III) centre crystallizes as an isolated mononuclear species. In order to generate heterometallic CPs, both complexes have been used as metallatectons upon their combination with different silver(I) salts. Upon reaction of (acacpy(2))Cu(dpm-py) with Ag(BF(4)) or Ag(TfO), 2- and 3-D heterometallic networks were obtained, respectively. In both cases, sheet type arrangements resulting from the binding of Ag(+) cations by three peripheral pyridyl groups were observed. These 2D sheets are further interconnected through Ag-π interactions with the pyrrolic rings. Under the same conditions, the combination of (acacpy(2))Co(dpm-py)(2) with Ag(TfO) leads to two networks differing by their connectivity patterns and dimensionality. Interestingly, whereas no Ag-π interactions were observed for the 2D network, a combination of coordination bonding with the pyridyl moieties and Ag-π interactions was detected for the 1D architecture.

Excited state properties and energy transfer within dipyrrin-based binuclear iridium/platinum dyads: the effect of ortho-methylation on the spacer.

Luminescent cyclometalated iridium complexes based on pyridyl appended dipyrrin ligands were prepared and characterized both in the solid state and in solution. The functionalization of the peripheral pyridyl moiety causes dramatic changes on the emission properties of both mono- and hetero- binuclear complexes. A detailed photophysical investigation of the two mononuclear derivatives of the [(Ppy)(2)Ir(dpm-py)] family (Ppy=2-phenylpyridine, dpm-py=5-(4-pyridyl)dipyrrin) was carried out. Introduction of methyl groups at the 3 and 5 positions on the pyridyl unit diminishes the non-radiative rate constant by locking the peripheral pyridyl group orthogonally to the dipyrrinato plane. Thus, they limit the rotational degree of freedom, as well as the charge-transfer character of the excited state. The coordination of these two complexes to a cyclometalated [(dppy)Pt] fragment (dppy=2,6-diphenylpyridine) led to the formation of binuclear species in which the iridium and platinum complexes behave as acceptors and donors, respectively. In these heterobinuclear compounds, the methyl groups do not influence the energy transfer efficiency, which is estimated to be above 90 %. However, they do limit the charge-transfer character of the acceptor's excited state, as well as its rotational degree of freedom, thus avoiding the detrimental effect upon the photophysical performance.

From insertion of rhodium acetate paddlewheels into functionalized 7-azaindole hydrogen-bonded dimers to infinite architectures.

In order to take advantage of the peculiar mode of interaction consisting in the combination of hydrogen and coordination bonding displayed by the 7-azaindole core towards tetraacetate paddlewheel type complexes, a series of new derivatives, bearing peripheral interacting sites at the position 3, have been prepared and their self-assembly into dimeric H-bonded species was established in the solid state. Furthermore, the heterochelate mode of binding was exploited both in the solid state and in solution using [Rh(2)(OAc)(4)] paddlewheel to generate discrete capped complexes resulting from the coordination of the pyridyl nitrogen atom to the axial position of the Rh(ii) cations and hydrogen bonding between the pyrrolic NH and an oxygen atom of one of the equatorial acetate groups. The extension to infinite hybrid networks was achieved using derivatives bearing self complementary H-bond donor and acceptor groups such as a carboxylic moiety.

Dithiolate-appended iridium(III) complex with dual functions of reducing and capping agent for the design of small-sized gold nanoparticles.

The unprecedented combined reduction of chloroauric acid and capping of the resulting gold nanoparticles in the absence of an external reducing agent are demonstrated using a novel heteroleptic Ir(III) complex incorporating a 4,5-diazafluorenedithiolate ligand. The reduction process in basic medium results from a cascade mechanism involving oxidation of the ligand, reduction of the gold salt, and stabilization and functionalization of the gold nanoparticles.

Dipyrrin based silver [2 + 2] metallamacrocycles.

The synthesis and characterization of a series of [2 + 2] metallamacrocycles based on combinations of silver salts AgX (X = BF(4)(-), PF(6)(-), SbF(6)(-), TfO(-)) with pyridyl, p-phenyl-pyridyl and p-phenyl-imidazolyl appended dipyrrin (dpm) derivatives is reported. In these species, the silver ion is linearly coordinated to one of the two pyrrolic groups of the dpm moiety through the nitrogen atom and to a N atom belonging to the peripheral coordinating group. The organisation of the cyclic complexes in the solid state is dependent on the nature of the anion X(-) and on the hydrogen bonding patterns formed with the pyrrolic NH group, acting as a donor. Furthermore, in some cases, d(10)-d(10) argentophilic interactions are observed between consecutive macrocyclic complexes in the crystalline phase. The robustness of some of the complexes obtained compounds was investigated by (1)H- and (13)C-NMR spectroscopy which revealed the structural integrity of the cyclic species in solution. A DOSY NMR study on the cyclic entity based on the imidazolyl appended dpm further assessed that the complex present in solution was indeed the [2 + 2] metallamacrocycle.