Metallo(salen)complexes as versatile building blocks for the fabrication of molecular materials and devices with tuned properties

The [M(salen)]complexes (M = transition metal such as V, Cr, Mn, Fe, Co, Ni, Cu, Pd)are high versatile coordination compounds, that can be easily immobilised in solid supports or used as building blocks for the assemblage of supramolecular systems, allowing the fabrication of sophisticated molecular materials. According to the composition and structure of the assembled materials, their properties can be fine-tuned and a wide range of applications is possible. This review starts with an overview on the [M(salen)]complexes and proceeds with a description of the main synthetic protocols developed for the preparation of [M(salen)]-based molecular materials, including their immobilisation onto several solid supports or their integration in supramolecular systems. To finish, several applications of [M(salen)]-based molecular materials are highlighted, which are aligned by four key thematic topics, considering current societal challenges: Heterogeneous Catalysis, Environmental Protection, Chemical Sensors and Sustainable Energy. In the Heterogeneous Catalysis topic is reviewed the application of [M(salen)]-based materials as heterogeneous catalysts in several organic chemical reactions, with high impact at industrial level, such as asymmetric oxidation or cycloaddition reactions. In the Environmental Protection topic is pointed out the importance of [M(salen)]-based materials for gas storage and for CO2 valorisation, through its capture and catalytic transformation into high-value products. In the Chemical Sensors topic is revised the use of [M(salen)]-based materials for ion-selective electrodes or as electrocatalysts for analyte detection. Lastly, in the Sustainable Energy topic, the application of [M(salen)]-based materials in a perspective of energy conversion, storage and saving is presented, considering their use as electrocatalysts for the oxygen reduction reaction, electrochromic materials, or their incorporation into supercapacitors, batteries or organic light-emitting diodes. We believe that this Review will be of interest for researchers working in any of these fields, especially those interested in [M(salen)]-based materials, as it gives an up-to-date revision of the diversity of [M(salen)]-based materials and related hot-topic applications.