We describe here the preparation of soft crystals using disilanyl macrocycle C4 possessing four p-phenylenes circularly connected by four flexible disilane bonds. Single crystals of C4 exhibited a reversible thermal single-crystal-to-single-crystal (SCSC) phase transition behavior between two crystal phases accompanied by remarkable mechanical motion (thermosalient effect), as revealed by thermal analyses and X-ray diffraction measurements. Detailed structural analyses implied that flexibility of the parallelogram disilanyl architecture and molecular packing mode via weak intermolecular interactions facilitated a concerted structural transformation (parallel crank motion) of macrocycles in the crystal, thus resulting in the SCSC phase transition accompanied by anisotropic shrinking/elongation of the cells to induce the thermosalient effect. This work explores a new area of organosilicon chemistry and presents the potential utility of disilanyl macrocycles as soft crystals.

Iron(iii) carbonyl complexes are stabilized by a pincer ligand containing pyridine-N, phenyl-C and thiolate-S donors and two axial phosphine ligands. The N,C,S-pincer iron(iii) carbonyl complexes show CO-releasing properties induced by visible light.

Light-induced CO release from newly synthesized N,C,S-pincer iron(III) carbonyl complexes with two phosphorus ligands- trans-[Fe(L-κ N,C,S)(CO)(PRR')]PF ([1]PF, R = Me, R' = Ph; [2]PF, R = R' = Me; [3]PF, R = R' = OEt)-were investigated. All the iron(III) carbonyl complexes were stable in solution and showed light-inducible CO release under ambient conditions. Studies on the wavelength dependence of photoreaction revealed that the phosphite complex [3]PF exhibited the most extended photosensitivity including all visible and a part of near-IR light (390-800 nm wavelengths). The phosphine complexes [1]PF and [2]PF showed sensitivity to only the higher-energy region of visible light (390-450 nm). Quantum-chemical calculations and spectroscopic data suggested that all complexes [1]PF-[3]PF have dπ-dπ excitation modes to depopulate Fe-C(carbonyl) bonding and potentially induce the CO release by irradiation of light in the near-IR region, although moderately weakened Fe-C(carbonyl) bonding due to stronger π-backbonding by the phosphite ligand rendered the excitation effective on the CO release exclusively in [3]PF.

A s-p extended aryldisilane,c omprising at hienopyrazine group as an acceptor fragment and phenothiazine groups as the donor moiety,h as been prepared through the introduction of two Si À Si bridges (compound 1). X-ray diffraction analysis determined the crystal structure of 1,a nd experimental and theoretical approaches investigated its optical properties.S olvatochromic studies revealed the dual emission of 1 in all solvents tested. Compound 1 also exhibited fluorescence in the solid state upon excitation with ahand-held UV lamp,a sw ell as mechanochromic luminescent properties. The packing mode in the crystal structure,v ariation of phenothiazine conformation, morphological changes between crystalline and amorphous phases are the major factors showing reversible fluorescence under external stimuli. A theoretical conformer study found that 1 exists in distinct conformational groups differing in Gibbs free energy by less than 3kcal mol À1 .T he conformer in the crystalline state of 1 can promote the complete separation of the HOMO and LUMO between the phenothiazine donor and the thienopyrazine acceptor,l inked by the disilane linker.H OMO-LUMO energy transition in the crystalline state is forbidden due to the lacko ff rontier orbital overlap.C rystalline state emission showed LUMO ! HOMOÀ1transition (locally excited (LE) state). In the amorphous state,t he partial presence of quasiaxial conformers allows intramolecular charge-transfer type emission via energy transfer from dominant quasi-equatorial conformers.T he strategy proposed in this work provides important guidance for developing stimuli-responsive materials with controlled excited states.

A series of diiron complexes of N,C,S-tridentate ligands containing a 6-, 5-, or 4-amino-2-pyridyl group, [{Fe(μ-L-κ 3 N,C,S)(CO) 2 }Fe(CO) 3 ] (2, L = o-apyBPT; 3, L = mapyBPT; 4, L = p-apyBPT), was synthesized: apyBPT is a doubly deprotonated form of 3′-(amino-2″-pyridyl)-1,1′-biphenyl-2-thiol. Complexes 2−4 were converted to the mononuclear iron(II) complexes trans-[Fe(L-κ 3 N,C,S)(CO)-(PMe 2 Ph) 2 ] (6, L = o-apyBPT; 7, L = m-apyBPT; 8, L = papyBPT). In 2 and 6, the o-amino group is close to Fe bound to the aminopyridyl group. Cyclic voltammograms of 2−4 exhibit two consecutive one-electron reduction events, and catalytic current for proton reduction appears in the presence of acetic acid. The reduction potentials of 2−4 are similar to each other, while the overpotential for proton reduction with o-amino complex 2 is ca. 0.2 V lower than those with 3 and 4. In the mononuclear complexes 6−8, the redox potentials for the Fe III /Fe II couple are dependent on the position of the amino group in the pyridine ring, which is described by electronic and steric effects of the amino group. Such effects on the redox potentials are suppressed in the diiron complexes because the reduction occurs at the diiron core with π-accepting CO ligands, which is supported by DFT calculations. The lower overpotential in 2 compared with 3 and 4 is attributed to the concerted effect of the amino group proximal to the iron center. The amino group probably acts as a proton acceptor and assists the formation of the H−H bond from a hydride on the iron centers and a proton bound to the amino group.