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

Synthesis and structural, magnetic and spectroscopic characterization of iron(III) complexes with in situ formed ligands from methyl-2-pyridyl ketone transformations

Reactions of methyl-2-pyridyl ketone, pyCOMe, with FeCl₃·6H₂O in various solvents gave complexes [Fe₄Cl₆(OMe)₂(L1)₂]·0.7MeCN·0.4MeOH (1·0.7MeCN·0.4MeOH) and [Fe₃Cl₄(bicine)(L2)]·Me₂CO·0.2H₂O (2·Me₂CO·0.2H₂O). The ligands (L1)^2- = pyCO(Me)CHCOpy (in 1) and (L2)^2- = pyCO(Me)CH₂CO(OMe)py (in 2) are formed in situ, through an aldol reaction-type mechanism between the carbanion pyC(O)CH₂^- (formed by the nucleophilic attack of the MeO^- in pyCOMe) and pyCOMe which results in the formation of a new C-C bond. The intermediate compound undergoes attack in the -CH₂- or -CO- group by a MeO^- group, and the new ligands (L1)^2- and (L2)^2-, respectively, are formed. The molecular structure of 1 consists of three corner-sharing [Fe₂O₂] rhombic units in cis-arrangement. The two terminal Fe^III ions display distorted square pyramidal geometry and the two central Fe^III ions are distorted octahedral. The molecular structure of 2 consists of two corner-sharing [Fe₂O₂] rhombic units, with the two terminal Fe^III ions in distorted square pyramidal geometry and the central Fe^III in distorted octahedral. The differentiation in the coordination environment of the Fe^III ions in 1-2 is reflected in the values of the Mössbauer hyperfine parameters. In agreement with theoretical calculations, the square pyramidal sites exhibit a smaller isomer shift value in comparison to the octahedral sites. Magnetic studies indicate antiferromagnetic interactions leading to an S = 0 ground state in 1 and to an S = 5/2 ground state in 2, consistent with Electron Paramagnetic Resonance spectroscopy. Mössbauer spectra of 2 indicate the onset of relaxation effects below 80 K. At 1.5 K the spectrum of 2 consists of magnetic sextets. The determined hyperfine magnetic fields are consistent with the exchange coupling scheme imposed by the crystal structure of 2. Theoretical calculations shed light on the differences in the electronic structure between the square pyramidal and the octahedral sites.

Indium(III)/2-benzoylpyridine chemistry: interesting indium(III) bromide-assisted transformations of the ligand

Reactions of 2-benzoylpyridine, (py)(ph)CO, with InX₃ (X = Cl, Br) in EtOH at room temperature have been studied. The InCl₃/(py)(ph)CO system has provided access to complex [InCl₃{(py)(ph)CO}(EtOH)]·{(py)(ph)CO} (1) and the byproduct {(pyH)(ph)CO}Cl (2). The reaction of InBr₃ with (py)(ph)CO has led to a mixture of (L)[InBr₄{(py)(ph)CO}] (3) and [In₂Br₄{(py)(ph)CH(O)}₂(EtOH)₂] (4), where L⁺ is the 9-oxo-indolo[1,2-a]pyridinium cation and (py)(ph)CH(O)^- is the anion of (pyridin-2-yl)methanol. Based on solubility and crystallisation time differences between the two components of the mixture, complex 4 was isolated in pure form, i.e. free from 3. The formations of the counterion L⁺ and the coordinated (py)(ph)CH(O)^- anion represent clearly InBr₃-promoted/assisted transformations. Reaction mechanisms have been proposed for the formation of 2, 3 and 4. Complex 4 could also be isolated by the reaction of InBr₃ and pre-formed (py)(ph)CH(OH) in EtOH. The solid-state structures of 1, 3 and 4 were determined by single-crystal X-ray crystallography, while the identity of the salt 2 was confirmed by microanalyses and a variety of spectroscopic techniques, including ESI-MS spectra. In the indium(III) complexes, the metal ions are 6-coordinate with a distorted octahedral geometry. The halogeno groups (Cl^-, Br^-) in the three complexes are terminal. The (py)(ph)CO molecule behaves as a N,O-bidentate (1.11) ligand in 1 and 3. A terminal EtOH ligand completes the coordination sphere of In^III in 1. The alkoxo oxygen atoms of the two 2.21 (py)(ph)CH(O)^- ligands doubly bridge the In^III centers in 4 creating a {InIII2(μ-OR)₂}⁴⁺ core; a nitrogen atom of one reduced organic ligand, two bromo ions and one terminal EtOH molecule complete the 6-coordination at each metal centre. Complexes 1, 3 and 4 were characterised by IR and Raman spectroscopies, and the data were discussed in terms of their known solid-state structures. Molar conductivity data and ¹H NMR spectra were used in an attempt to probe the behaviour of the complexes in DMSO. The to-date observed metal ion-assisted/promoted transformations of (py)(ph)CO are also discussed.

Pentanuclear Thorium(IV) Coordination Cluster from the Use of Di(2-pyridyl) Ketone

The Th(NO₃)₄·5H₂O/di(2-pyridyl) ketone [(py)₂CO] reaction system gives a pentanuclear cluster containing the doubly deprotonated form of the gem-diol derivative of the ligand. The cluster consists of a tetrahedral arrangement of four Th^IV ions centered on the fifth ion, which is the first characterized Th^IV₅ complex. The analysis of its structure reveals that this is a Kuratowski-type coordination compound.