Amidine/Amidinate Cobalt Complexes: One-Pot Synthesis, Mechanism, and Photocatalytic Application for Hydrogen Production.

A new synthetic route was carried out via a one-pot reaction to prepare a novel series of amidine/amidinate cobalt complexes 8-10 by mixing ligand 2 (6-pyridin-2-yl-[1,3,5]-triazine-2,4-diamine) with Co(II) in acetonitrile or benzonitrile. We observed that a change of solvent from methanol (used in complex 7, previously reported) to nitrile solvents (MeCN and PhCN) led to the in situ incorporation of the amidine group, ultimately forming 8-10. So far, this is a unique method reported to introduce amidine/amidinate groups into a pyridinyl-substituted diaminotriazine complex. Remarkably, the single crystal X-ray diffraction study (SCXRD) of these new compounds reveals associations involving Janus DATamidine and Janus DATamidinate. A mechanism is proposed to explain the formation of amidine/amidinate groups by investigating the single crystal structures of the possible intermediates 11 and 12 where the cobalt ion acts as a template. These amidine/amidinate cobalt complexes were used as a model to assess the photocatalytic activity for the hydrogen evolution reaction (HER). Complexes 9 and 10 show a 74% and 86% enhancement, respectively, of the catalytic activity towards the HER compared to complex 7. This highlights the structure-property relationship. By examining the novel cobalt complexes described here, we discovered the following: (i) a method to introduce an amidine group into a pyridine DAT-based complex, (ii) the efficiency of amidine complexes to form multiple hydrogen bonds to direct the molecular organization, (iii) the plausible mechanism of formation of amidines based on the SCXRD study, (iv) the modification of the final structure and hence the final properties by varying the reaction conditions, and (v) the utility of amidine complexes towards photocatalytic HER activity.

Conversion of Methane into Methanol Using the [6,6'-(2,2'-Bipyridine-6,6'-Diyl)bis(1,3,5-Triazine-2,4-Diamine)](Nitrato-O)Copper(II) Complex in a Solid Electrolyte Reactor Fuel Cell Type.

The application of solid electrolyte reactors for methane oxidation to co-generation of power and chemicals could be interesting, mainly with the use of materials that could come from renewable sources and abundant metals, such as the [6,6'- (2, 2'-bipyridine-6, 6'-diyl)bis (1,3,5-triazine-2, 4-diamine)](nitrate-O)copper (II) complex. In this study, we investigated the optimal ratio between this complex and carbon to obtain a stable, conductive, and functional reagent diffusion electrode. The most active Cu-complex compositions were 2.5 and 5% carbon, which were measured with higher values of open circuit and electric current, in addition to the higher methanol production with reaction rates of 1.85 mol L-1 h-1 close to the short circuit potential and 1.65 mol L-1 h-1 close to the open circuit potential, respectively. This activity was attributed to the ability of these compositions to activate water due to better distribution of the Cu complex in the carbon matrix as observed in the rotating ring disk electrode experiments.

Programmed Molecular Construction: Driving the Self-Assembly by Coordination and Hydrogen Bonds Using 6-(Pyridin-2-yl)-1,3,5-triazine-2,4-diamine with M(NO3)2 Salts.

A new series of hydrogen-bonded metallotecton networks 6-9 of the general formula [M(2)2(NO3)2] were obtained from the reaction of 6-pyridin-2-yl-[1,3,5]-triazine-2,4-diamine 2 with transition-metal ions [M: Co(II), Ni(II), Cu(II), and Zn(II)]. Their supramolecular networks and associated properties were characterized by single-crystal and powder X-ray diffraction, IR, solid-state UV-vis spectroscopy, and thermogravimetric analysis associated with differential scanning calorimetry. On the basis of standard patterns of coordination involving 2,2'-bipyridine and simple derivatives, compound 2 binds transition-metal ions with predictable constitution and the diaminotriazinyl (DAT) groups serve orthogonally to ensure the intermetallotecton interactions by hydrogen bonding according to well-established motifs I-III. As expected, compound 2 formed octahedral 2:1 metallotectons with M(NO3)2, and further self-assembled by hydrogen bonding of the DAT groups to produce pure, crystalline, homogeneous, and thermally stable materials. In these structures, nitrate counterions also play an important role in the cohesion of intermetallotectons to form two-dimensional and three-dimensional networks. These results illustrated the effectiveness of the synthetic approach to create a wide range of novel ordered materials with controllable architectures and tunable properties achieved by varying the central metal ion. Crystal morphologies of 6-9 were also investigated by scanning electron microscopy and calculation using Bravais-Friedel-Donnay-Harker method from their single-crystal structure.

Syntheses of mono and bimetallic cyamelurate polymers with reversible chromic behaviour.

Ordered coordination polymers (CPs) have been an interesting class of materials for scientific and industrial research for the last few decades. However, their availability as well as certain economic and environmental limitations could slow down their use in many applications. Herein, we present room temperature synthesis in water of a series of CPs (four metal-organic polymers MOPs-(1-4) and three mixed metal-organic polymers MMOPs-(5-7)). All MMOPs were found to be isostructural to MOPs as determined by XRD. Remarkably, MOPs-(2 and 3) and MMOPs-(5-7) exhibit switchable chromic behaviour associated with reversible structural transformation which was facilitated by dehydration/rehydration or solvent exchange (MeOH/H2O) processes. Chromic behaviour and its mechanism were investigated using IR, solid-state UV-Vis, XRD, PXRD and TGA indicating the coordination/de-coordination of water molecules to be the key factor that influences the colour changes. These results render the potential application of MOPs and MMOPs as sensor materials.

Mimicking 2,2':6',2'':6'',2'''-quaterpyridine complexes for the light-driven hydrogen evolution reaction: synthesis, structural, thermal and physicochemical characterizations.

The synthetic difficulties associated with quaterpyridine (qtpy) complexes have limited their use in the formation of various metallosupramolecular architectures in spite of their diverse structural and physicochemical properties. Providing a new facile synthetic route to the synthesis of functionalised qtpy mimics, we herein report the synthesis of three novel -NH2 functionalized qtpy-like complexes 12-14 with the general formula M(C16H14N12)(NO3)2 (M = Co(ii), Ni(ii) and Cu(ii)) in high yield and purity. Characterization of these complexes has been done by single crystal X-ray diffraction (SCXRD), thermogravimetric analysis, UV-Vis, infrared, mass spectrometry and cyclic voltammetry. As indicated by SCXRD, in all the synthesized complexes, the metal ions show a strongly distorted octahedral coordination geometry and typical hydrogen bonding networks involving DAT groups. In addition, complexes 12-14 have been analyzed as potential photocatalysts for hydrogen evolution reaction (HER) displaying good turnover numbers (TONs). Hydrogen produced from these photocatalysts can serve as the possible alternative for fossil fuels. To the best of our knowledge, this is the only study showcasing -NH2 functionalized qtpy-like complexes of Co(ii), Ni(ii) and Cu(ii) and employing them as photocatalysts for HER. Thus, a single proposed strategy solves two purposes-one related to synthesis while second is related to our environment.