Copper Complexes of Benzoylacetone Bis-Thiosemicarbazones: Metal and Ligand Based Redox Reactivity

Abstract

Bis-thiosemicarbazones derived from the b-diketone benzoylacetone (H 3 banR, R ¼ Me, Et, Ph) are potentially tetradentate N 2 S 2 ligands whose coordination chemistry with copper is reported. In the absence of oxygen and in the presence of base they form anionic Cu II complexes of the fully deprotonated ligands [Cu II (banR)]-. Upon exposure to atmospheric oxygen they undergo a complex series of reactions leading to two types of products; one a ligand oxidised ketone complex [Cu II (banRO)] and the other an unprecedented dimeric di-Cu III complex [(Cu III (banR)) 2 ] depending on the R substituent. Time-resolved UV-vis spectroscopy, cyclic voltammetry, spectroelectrochemistry, and electron paramagnetic resonance (EPR) spectroscopy have been used to identify intermediates on the way to stable products formed under both anaerobic and aerobic conditions. It is found that both ligand-centred and Cu-centred oxidation reactions are occurring in parallel leading to this unusually complicated mixture of products.

X-ray absorption and emission spectroscopy of N2S2 Cu(ii)/(iii) complexes

“…Furthermore, the low-spin S = 0 d 8 electronic configuration is typical for four-coordinate (distorted) square-planer Cu(III) complexes with redox innocent ligands. 7,[9][10][11]45 An S = 1 observation has only yet occurred in six-coordinate Cu(III) species, which exhibit S = 1 ground states due to the O h ligand field (would also be true for T d ligand fields). 6,46 The singlet ground state is further supported by the single point energy of the singlet state being calculated ∼8.1 kcal mol −1 lower in energy than the triplet state.…”

“…9 A structurally similar bis (thiosemicarbazone) ligand was also found to be capable of forming a novel dimeric Cu(III) complex in a comparable N 2 S 2 coordination environment. 10 The non-innocence of Schiff bases and the ability of these types of ligands to support both high-valent Cu(III) 11,12 and Fe (IV) 13,14 oxidation states has been investigated in depth by various spectroscopic, structural and computational methods. Specifically, these dithiocarbazate Schiff bases stabilize a formally high-valent Cu(III) oxidation state, and support for this assignment is offered in the form of electrochemical analysis and the electron paramagnetic resonance (EPR) signal observed from chemical reduction of the Cu(III) complex to the S = 1/2 Cu(II) species.…”

Structure and bonding trends of bisthiosemicarbazones: An overview

“…A number of bisthiosemicarbazones are known with various substituents on carbon atoms of the CC linkage and amino nitrogen. [ 54,81,83–103 ] The ligands with methyl, ethyl, or phenyl substituents on CC linkage are known ( A1 – A6 ) (Chart 1). These ligands were prepared by refluxing thiosemicarbazide and 1,2‐diketone in 2:1 M ratio.…”

Influence of the Reaction Conditions in the Crystal Structures of Zn(II) and Ni(II) Coordination Compounds with a Dissymmetric Bis(Thiosemicarbazone) Ligand

“…The most common one is as N,S bidentate chelate [3,4], coordination mode that affords the formation of a very stable five-membered chelate ring, but many others are described in the literature, for example S monodentante [5,6], N,S bidentate chelate and S bridge [7,8] Crystals 2022, 12, 310 2 of 12 or N,S bidentate chelate and N bridge [9]. This, together with the control of protonation/deprotonation and the nature of auxiliary anions, lead to the formation of different structures such as monomers [10][11][12], dimers [13][14][15] or coordination polymers [16][17][18]. In addition to their fascinating structural properties, TSCs have a wide range of applications in different fields as catalysis [19][20][21], metal detoxification [22][23][24], metal sensing [25][26][27] or medicine [28][29][30][31].…”