A multiprotic indole-based thiocarbohydrazone in the formation of mono-, di- and hexa-nuclear metal complexes

A new thiocarbohydrazone (LH4) derived from indole-7-carbaldehyde was synthesized and reacted with NiII, PdII, PtII, CuI and AgI salts to bind the metals in various coordination fashions, forming complexes with different nuclearities. The reaction with CuCl in the presence of PPh3 produced a dinuclear CuI complex with the formula [Cu2Cl2(LH4)2(PPh3)2], in which LH4 binds the metals as a neutral μ2-S-donor ligand. The reaction of the thiosemicarbazone with AgI resulted in the formation of a hexanuclear complex featuring an Ag6S6 core. The ligand in this complex is monoanionic and uses the sulfur and a hydrazinic nitrogen atom in binding to the metals. The reaction of LH4 with [MCl2(PPh3)2] (M = NiII, PdII and PtII) at room temperature yielded complexes of the type [M(LH2)(PPh3)]. The thiocarbohydrazone in these complexes takes advantage of one indole N atom donor to act as a dianionic NNS tridentate ligand. A modification of the conditions of the reaction with the PdII salt led to the formation of the dinuclear complex [Pd2Cl(LH)(PPh3)3]. In this molecule, the thiocarbohydrazone is triply deprotonated and chelates one metal center by its dianionic NNS pocket, while coordinating the second metal ion through a hydrazinic N atom. The structure of the molecules was studied by X-ray crystallography and NMR spectroscopy.

Graphical abstractBis(indole-7-carbaldehyde)thiocarbohydrazone, carrying four labile hydrogens, shows variable degrees of deprotonation and coordination modes to form mononuclear NiII, PdII and PtII, dinuclear CuI and PdII and hexanuclear AgI complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide