Indium(III) in the “Periodic Table”
of Di(2-pyridyl) Ketone: An Unprecedented Transformation of the Ligand
and Solid-State 115In NMR Spectroscopy as a Valuable Structural
Tool
posted on 2021-03-22, 04:35authored byChristina Stamou, Wassilios Papawassiliou, José P. Carvalho, Konstantis F. Konidaris, Vlasoula Bekiari, Pierre Dechambenoit, Andrew J. Pell, Spyros P. Perlepes
Reactions of di(2-pyridyl) ketone,
(py)2CO, with indium(III)
halides in CH3NO2 have been studied, and a new
transformation of the ligand has been revealed. In the presence of
InIII, the CO bond of (py)2CO is subjected
to nucleophilic attack by the carbanion –:CH2NO2, yielding the dinuclear complexes [In2X4{(py)2C(CH2NO2)(O)}2] (X = Cl, 1; X = Br, 2; X = I, 3) in moderate to good yields. The alkoxo oxygens of the two
η1:η2:η1-(py)2C(CH2NO2)(O)− ligands
doubly bridge the InIII centers and create a {In2(μ2-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 115In 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 CQ 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 δiso values
fall in the range 130 ± 30 to −290 ± 60 ppm. The
calculated CQ and asymmetry parameter
(ηQ) 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 115In NMR is an effective solid-state technique for
the study of indium(III) complexes.