Atmospheric Carbon Dioxide Capture as Carbonate into a Luminescent Trinuclear Cd(II) Complex with Tris(2-aminoethyl)amine Tripodal Ligand

Spontaneous atmospheric CO2 capture as carbonate anion occurred in the synthesis of a trinuclear Cd(II) complex with tris(2-aminoethyl)amine ligand. In reaction two types of compounds were obtained and structurally characterized by X-ray diffraction on a single crystal: initially [{Cd(tren)}3(tren)](ClO4)6·2H2O (1) and subsequently [{Cd(tren)}3(tren)][{Cd(tren)}3(µ3-ηCO3)](ClO4)10 (2). The carbonate anion replaces partially the bridging tren molecule and coordinates in a µ3 fashion. The luminescent properties of the compounds were investigated.

Solvent-Induced Hysteresis Loop in Anionic Spin Crossover (SCO) Isomorph Complexes

Reaction of Fe(II) with the tris-(pyridin-2-yl)ethoxymethane (py3C-OEt) tripodal ligand in the presence of the pseudohalide ancillary NCSe- (E = S, Se, BH3) ligand leads to the mononuclear complex [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCSe)3]2·2CH3CN (3), which has been characterised as an isomorph of the two previously reported complexes, Fe(py3C-OEt)2][Fe(py3C-OEt)(NCE)3]2·2CH3CN, with E = S (1), BH3 (2). X-ray powder diffraction of the three complexes (1–3), associated with the previously reported single crystal structures of 1–2, revealed a monomeric isomorph structure for 3, formed by the spin crossover (SCO) anionic [Fe(py3C-OEt)(NCSe)3]− complex, associated with the low spin (LS) [Fe(py3C-OEt)2]2+ cationic complex and two solvent acetonitrile molecules. In the [Fe(py3C-OEt)2]2+ complex, the metal ion environment involves two py3C-OEt tridentate ligands, while the [Fe(py3C-OEt)(NCSe)3]− anion displays a hexacoordinated environment involving three N-donor atoms of one py3C-OEt ligand and three nitrogen atoms arising from the three (NCSe)− coligands. The magnetic studies for 3 performed in the temperature range 300-5-400 K, indicated the presence of a two-step SCO transition centred around 170 and 298 K, while when the sample was heated at 400 K until its complete desolvation, the magnetic behaviour of the high temperature transition (T1/2 = 298 K) shifted to a lower temperature until the two-step behaviour merged with a gradual one-step transition at ca. 216 K.

Solvent-Induced Hysteresis Loop in Anionic Spin Crossover (SCO) Isomorph Complexes

Reactions of Fe(II) with the tris-(pyridin-2-yl)ethoxymethane (py3C-OEt) tripodal ligand in presence of the pseudohalide ancillary NCE- (E = S, Se, BH3) ligands led to a series of three mononuclear complexes formulated as [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCE)3]2·2CH3CN, with E = S (1), BH3 (2) and Se (3). Single crystal characterizations (complexes 1-2) and X-ray powder diffraction (complexes 1-3) reveal monomeric isomorph structures formed by the spin crossover (SCO) anionic [Fe(py3C-OEt)(NCE)3] complex, associated with the low spin (LS) cationic [Fe(py3C-OEt)2]2+ complex and two solvent acetonitrile molecules. In the [Fe(py3C-OEt)2]2+ cation, the Fe(II) is coordinated by two py3C-OEt tridentate ligands, while the [Fe(py3C-OEt)(NCE)3] anion displays a hexacoordinated environment involving three N-donor atoms of one py3C-OEt ligand and three nitrogen atoms arising from of the three (NCE) coligands. The magnetic studies show the presence of gradual SCO behavior for the three complexes: a one-step transition around 205 K for 1 and two step-transitions for compounds 2 and 3, centred at 245 K and 380 K for 2, and at 170 K and 298 K for 3. The magnetic behaviors of complexes 1 and 2 remain unchanged when heating up to 500 K, while complex 3 shows significant changes which are caused by the crystallisation solvent loss above room temperature.

A Versatile Tripodal Ligand for Sensitizing Lanthanide (LnIII) Ions and Color Tuning

Lanthanide (LnIII) ions were successfully chelated and sensitized with a tripodal ligand. The absolute LnIII-centered emission efficiencies were ~3% for both the europium(III) (EuIII) and terbium (TbIII) complexes and up to 54% for the cerium(III) (CeIII) complex. The differences in emission quantum yields for the early lanthanides (CeIII) and the mid lanthanides (EuIII and TbIII) were attributed to their d–f and f–f nature, respectively. Despite the low quantum yield of the EuIII complex, the combination of the residual ligand fluorescence and the red EuIII emission resulted in a bluish-white material with the Commission Internationale de l’Eclairage (CIE) coordinates (0.258, 0.242). Thus, metal complexes of the ligand could be used in the generation of single-component white-light-emitting materials.