Coordination chemistry of S-substituted isothiosemicarbazides and isothiosemicarbazones

While thiosemicarbazides and thiosemicarbazones, along with their metal complexes are well-presented in the literature, the coordination chemistry of S-substituted isothiosemicarbazides and their derivatives is far less known to the inorganic chemistry community. This review is an attempt to fill this gap. The unique identity of isothiosemicarbazides is expressed by the presence of the two amine groups in their structure, one hydrazinic and another isothioamidic, which are not related by symmetry and potentially are able to create a distinct ligand field. Another worthy of noting peculiarity is the reduced electron donating ability of the thioether sulfur atom when compared to that in thiosemicarbazide. These features were widely exploited for demonstration of the fascinating aspects of the coordination chemistry of isothiosemicarbazides, such as noninnocent redox behaviour and specific reactivity. Particular attention is paid to the use of isothiosemicarbazides for stepwise template building of tetradentate ligands with a varied set of donor atoms, e.g. N2O2, N2S2, N2SO, N3O, N-4, including N-4 macrocyclic systems with cis- and trans-arrangement of -SR groups. Successful demetallation procedures in many cases allowed studies of the coordination chemistry of first-, second- and third-row transition metals, when they are not effective as templates. Particular examples of the catalytic coordination template effect with the same aim of assembly of new ligand products are discussed. The cytotoxicity aspects when compared to thiosemicarbazides and thiosemicarbazones, as well as the use of metal complexes based on isothiosemicarbazones in catalysis, anion recognition, cation sensing, spin-transition are also briefly discussed. (C) 2019 Elsevier B.V. All rights reserved.