The main objective of this project is the study of indium as a surrogate for lanthanides and actinides, based on the assumption that cations of similar ionic radii will form similar oxide structures. Chosen as convenient starting materials, a new family of In(III) complexes of formula mer-[InCl3(pz*H)3] and trans-[InCl2(4-Me-pzH)4]+, (pz*H = pzH, 4-Cl-pzH, 4-Br-pzH, 4-I-pzH, 4-Ph-pzH, 4-Me-pzH, and 3,5-Me2-pzH) was synthesized and characterized by SCXRD, elemental analysis, FTIR, and VT-1H NMR. The results showed the labile nature of indium complexes, and the VT-1H NMR revealed a complex interplay of simultaneous coordination flexibility, dissociation, and tautomerization processes.
Subsequently, higher nuclearity complexes were obtained upon addition of base under various reaction conditions. Hexanuclear complexes of general formula [In6Cl6(m3-OH0.5)(m-OH)6(m-pz*)6]3- (pz* = pz, 4-Cl-pz, 4-Ph-pz) and polymeric species [In(µ-pz*)3]n (pz* = pz, 4-Cl-pz, 4-I-pz, 4-Ph-pz) were isolated and characterized by SCXRD, elemental analysis, 1H NMR, and FTIR. The hexanuclear indium complexes have a novel motif formed by two trianionic units bridged by both oxo/hydroxo groups. The luminescence properties of the polymeric species showed longer emission lifetimes than previously reported indium luminophores.
Upon deprotonation of the mononuclear indium complexes and the reaction with iron salts both heterobimetallic and homometallic species were isolated. Complexes of general formula [Fe8-xInxCl4(m4-O)4(m-pz)12]and [In6-xFexCl6(m3-OH0.5)(m-OH)6(m-pz*)6]3- were isolated and characterized by SCXRD, ESI-MS and SEM-EDS.
The serendipitously prepared complexes [Fe7In2Cl4(µ3-O)2(µ3-OH)2(µ3-OH0.5)2 (µ-OH)2(µ-4-Cl-pz)12(4-Cl-pzH)2](Et3NHCl), (HNEt3)2[Fe6Cl2(µ3-O)2(µ-OH)4(µ-4-Cl-pz)10] and [Fe5Cl3(µ4-O)(µ3-O)(µ-OH)2(µ-4-I-pz)6(4-I-pz)4].(Et2O) were isolated and characterized crystallographically. The latter, with an all-ferric Fe5O4-core with a rare “incomplete cubane” topology, like the [Mn4CaO5]-unit in Photosystem II, was also studied electrochemically, revealing two reductive and one oxidative step to mixed-valent species.