Two new homometallic coordination polymers based on a carboxylate-functionalized salen ligand

When the Metal Makes the Difference: Template Syntheses of Tridentate and Tetradentate Salen-Type Schiff Base Ligands and Related Complexes

The reaction of organic molecules mediated by a metal center (template synthesis) can result in a final connectivity that may differ from the one obtained in the absence of the metal. The condensation of carbonyl fragments with primary amines form C=N iminic bonds, the so-called Schiff bases, which can act as ligands for the templating metal center by means of the lone pair on the nitrogen atom. This review focuses on the template methods for the reaction between a carbonyl compound (mainly salicylaldehyde) and a primary aliphatic diamine able to prevent the double condensation on both amine groups and obtain tridentate N2O ligands. These adducts, still having one free amino group, can further react, yielding tetradentate salen-type Schiff base ligands. A screening over the transition metals able to show such a template effect will be presented, with particular attention to copper(II), together with their peculiar reactivity and the available crystal structure of the metal complexes and related coordination geometries.

Separation of Metal-N4 Units in Metal-Organic Framework for Preparation of M-Nx/C Catalyst with Dense Metal Sites

Metal and nitrogen codoped carbon (M-N_x/C) materials with good metal dispersion in a carbon matrix have attracted great attention because they can efficiently catalyze various kinds of chemical/electrochemical reactions. However, the existing strategies for preparing M-N_x/C materials still face the challenge of metal site aggregation when the carbon skeleton in the precursor is substantially lost during pyrolysis. Herein, we propose a general strategy that the increase of metal site density and inhibition of metal aggregation could be realized by separating M-N₄ units in metal-organic frameworks (MOFs). The metal sites can be well separated and distributed in carbon materials during the pyrolysis of a metal-coordinated block copolymer, one of the specific MOFs. The strategy can be widely applicable for the synthesis of M-N_x/C materials with dense metal sites, such as Fe-, Mn-, Ni-, and Co-N_x/C materials, which are potentially used as the efficient catalysts for various kinds of reactions. Taking Fe-N_x/C as a model oxygen reduction reaction (ORR) electrocatalyst, it shows the ORR half-wave potentials of 0.90 and 0.81 V vs RHE in alkaline and acidic electrolytes, respectively.

An unprecedented 3D architecture based on a Nb/W mixed-addendum polyoxometalate and lanthanide–organic complex: synthesis, crystal structure and properties

For the first time, a 3D framework based on lanthanide-containing Nb/W mixed-addendum polyoxometalate has been obtained by utilizing the steam-assisted conversion method.