Indium(III) in the "Periodic Table" of Di(2-pyridyl) Ketone: An Unprecedented Transformation of the Ligand and Solid-State 115 In NMR Spectroscopy as a Valuable Structural Tool.

Reactions of di(2-pyridyl) ketone, (py) ₂ CO, with indium(III) halides in CH ₃ NO ₂ 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 ^- :CH ₂ NO ₂ , yielding the dinuclear complexes [In ₂ X ₄ {(py) ₂ C(CH ₂ NO ₂ )(O)} ₂ ] (X = Cl, 1 ; X = Br, 2 ; X = I, 3 ) in moderate to good yields. The alkoxo oxygens of the two η ¹ :η ² :η ¹ -(py) ₂ C(CH ₂ NO ₂ )(O) ^- ligands doubly bridge the In ^III centers and create a {In ₂ (μ 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 ¹¹⁵ In 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 In ^III sites for 3 , while the δ _iso values fall in the range 130 ± 30 to -290 ± 60 ppm. The calculated C _Q and asymmetry parameter (η _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 ¹¹⁵ In NMR is an effective solid-state technique for the study of indium(III) complexes.