Hypervalent triphenyl and diphenyl tin coordination compounds derived from 2-(1H-benzimidazol-2-yl)phenol

Vapochromic Luminescent π-Conjugated Systems with Reversible Coordination-Number Control of Hypervalent Tin(IV)-Fused Azobenzene Complexes

The dynamic and reversible changes of coordination numbers between five and six in solution and solid states, based on hypervalent tin(IV)-fused azobenzene (TAz) complexes, are reported. It was found that the TAz complexes showed deep-red emission owing to the hypervalent bond composed of an electron-donating three-center four-electron (3c-4e) bond and an electron-accepting nitrogen-tin (N-Sn) coordination. Furthermore, hypsochromic shifts in optical spectra were observed in Lewis basic solvents because of alteration of the coordination number from five to six. In particular, vapochromic luminescence was induced by attachment of dimethyl sulfoxide (DMSO) vapor to the coordination point at the tin atom accompanied with a crystal-crystal phase transition. Additionally, the color-change mechanism and degree of binding constants were well explained by theoretical calculation. To the best of our knowledge, this is the first example of vapochromic luminescence by using stable and variable coordination numbers of hypervalent bonds.

Ferrocene-Containing Tin(IV) Complexes Based on o-Benzoquinone and o-Iminobenzoquinone Ligands. Synthesis, Molecular Structure, and Electrochemical Properties

The addition of different substituted o-benzoquinones and o-iminobenzoquinones to tin(II) bis(o-iminophenolates) of the types (Fc-IP)₂Sn^II and (Fc-4,6-IP)₂Sn^II (where Fc-IP is anion 2-(ferrocenylmethyleneamino)phenolate [Fc-C(H)═N(C₆H₄)O^-] and Fc-4,6-IP is anion 2-(ferrocenylmethyleneamino)-4,6-di-tert-butylphenolate [Fc-C(H)═N(4,6-tBu-C₆H₂)O^-]) in tetrahydrofuran leads to the oxidation of Sn(II) to Sn(IV) with formation of the corresponding tin(IV) catecholates (Fc-4,6-IP)₂Sn^IV(3,6-Cat) (1), (Fc-IP)₂Sn^IV(3,6-Cat) (2), (Fc-4,6-IP)₂Sn^IV(4-Cl-3,6-Cat) (3), (Fc-IP)₂Sn^IV(4-Cl-3,6-Cat) (4), (Fc-4,6-IP)₂Sn^IV(4,5-Cl₂-3,6-Cat) (5), and (Fc-IP)₂Sn^IV(4,5-Cl₂-3,6-Cat) (6) or the o-amidophenolates (Fc-4,6-IP)₂Sn^IV(AP-Me) (7), (Fc-IP)₂Sn^IV(AP-iPr) (8), and (Fc-4,6-IP)₂Sn^IV(AP-iPr) (9). Here ligands 3,6-Cat, 4-Cl-3,6-Cat, and 4,5-Cl₂-3,6-Cat are dianions 3,6-di-tert-butyl-, 4-chloro-3,6-di-tert-butyl-, and 4,5-dichloro-3,6-di-tert-butylcatecholates, respectively, and AP-Me and AP-iPr are dianions 4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-amidophenolate and 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolate, respectively. Complexes 1-9 have been characterized in detail by IR spectroscopy, cyclic voltammetry, and ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy. The molecular structures of tin(IV) complexes 5, 7, and 9 in the crystalline state were determined by single-crystal X-ray diffraction analysis. Complexes demonstrate a series of successive oxidations involving alternately catecholato/o-amidophenolato centers and ferrocenyl moieties. The relative oxidation potentials of these redox centers depend on the acceptor properties of the redox-active chelating O,O' or O,N ligand. An increase in the acceptor properties of redox-active o-quinonato-type ligands leads to an increase in the oxidation potentials of redox ligands as well as the following oxidation of ferrocenyl group(s). In two series of complexes, (Fc-4,6-L)₂SnL' and (Fc-L)₂SnL', where L' is AP-iPr, AP-Me, 3,6-Cat, 4-Cl-3,6-Cat, and 4,5-Cl₂-3,6-Cat, a more pronounced convergence of the oxidation potentials of the redox-active o-quinonato ligand and ferrocenyl group occurs in the series (Fc-L)₂SnL'.

Complexes containing benzimidazolyl-phenol ligands and Ln(III) ions: Synthesis, spectroscopic studies and preliminary cytotoxicity evaluation

Fourteen new complexes were obtained from Ln(III)(NO₃)₃∙n-H₂O and the chromophores 2-(1H-benzo[d]imidazol-2-yl)-phenol (Bzp1) or 2-(5-methyl-1H-benzo[d]imidazol-2-yl)-phenol (Bzp2). The complete characterization allowed us to assign unequivocally the structures of all the complexes. The techniques used for this purpose were Ultraviolet-Visible (UV-Vis) and Fourier-Transform Infrared (FT-IR) spectroscopies, High-Resolution Mass Spectrometry (HRMS), Magnetic Susceptibility (MS), Elemental Analysis (EA) and Molar Conductivity (MC). HRMS allowed us to find the molecular ion and its isotopic pattern. The FT-IR spectral data suggested that benzimidazolyl-phenol ligands coordinate with Ln(III) ions through iminic nitrogen and phenolic oxygen. Thermogravimetric Analysis (TGA) studies of NdBzp1 and GdBzp2 complexes indicate the presence of lattice water along with three nitrates and two benzimidazolyl-phenol ligands; the thermal decomposition was consistent with the minimal formula suggested by EA. The coordination type of the benzimidazolyl-phenol ligands, the geometry and the structural organization of these coordination complexes have been interpreted by Density Functional Theory (DFT) calculations, and they coincided with the physicochemical data suggesting a coordination number eight for the Ln(III) ions. The cytotoxicity of the chromophores and their coordination complexes was tested against a cancer cell line (HeLa), as compared with structure/support cells (NIH-3T3) and defense cells (J774A.1), revealing that three coordination complexes showed moderate cytotoxicity against the cell lines studied.