Indium(Iii) In The "Periodic Table" Of Di(2-Pyridyl) Ketone: An Unprecedented Transformation Of The Ligand And Solid-State In-115 Nmr Spectroscopy As A Valuable Structural Tool

Reactions of di(2-pyridyl) ketone, (py)(2)CO, with indium(III) halides in CH3NO2 have been studied, and a new transformation of the ligand has been revealed. In the presence of In-III, the C=O bond of (py)(2)CO is subjected to nucleophilic attack by the carbanion -:CH2NO2, yielding the dinuclear complexes [In2X4{(py)(2)C(CH2NO2)(O)}(2)] (X = Cl, 1; X = Br, 2; X = I, 3) in moderate to good yields. The alkoxo oxygens of the two eta(1):eta(2):eta(1)-(py)(2)C(CH2NO2)(O)- ligands doubly bridge the In-III centers and create a {In-2(mu(2)-OR)(2)}(4+) core. Two pyridyl nitrogens of different organic ligands and two terminal halogeno ions complete a distorted-octahedral stereochemistry around each In(III) ion. After maximum excitation at 360 or 380 nm, the solid chloro complex 1 emits blue light at 420 and 440 nm at room temperature, the emission being attributed to charge transfer within the coordinated organic ligand. Solid-state In-115 NMR spectra, in combination with DFT calculations, of 1-3 have been studied in detail at both 9.4 and 14.1 T magnetic fields. The nuclear quadrupolar and chemical shift parameters provide valuable findings concerning the electric field gradients and magnetic shielding at the nuclei of indium, respectively. The experimentally derived C-Q values are 40 +/- 3 MHz for 1, 46 +/- 5 MHz for 2, and 50 +/- 10 and 64 +/- 7 MHz for the two crystallographically independent InIII sites for 3, while the diso values fall in the range 130 +/- 30 to -290 +/- 60 ppm. The calculated C-Q and asymmetry parameter (eta(Q)) values are fully consistent with the experimental values for 1 and 2 and are in fairly good agreement for 3. The results have been analyzed and discussed in terms of the known (1, 3) and proposed (2) structural features of the complexes, demonstrating that In-115 NMR is an effective solid-state technique for the study of indium(III) complexes.