Second-Harmonic Generation and Photoluminescence Properties of Sn(II)- and Bi(III)-Based Lone Pair Cation–Pyridine Dicarboxylate Coordination Compounds

Polymorphism and Structural Variety in Sn(II) Carboxylate Coordination Polymers Revealed from Structure Solution of Microcrystals

The crystal structures of four coordination polymers constructed from Sn(II) and polydentate carboxylate ligands are reported. All are prepared under hydrothermal conditions in KOH or LiOH solutions (either water or methanol-water) at 130-180 °C and crystallize as small crystals, microns or less in size. Single-crystal structure solution and refinement are performed using synchrotron X-ray diffraction for two materials and using 3D electron diffraction (3DED) for the others. Sn2 (1,3,5-BTC)(OH), where 1,3,5-BTC is benzene-1,3,5-tricarboxylate, is a new polymorph of this composition and has a three-dimensionally connected structure with potential for porosity. Sn(H-1,3,5-BTC) retains a partially protonated ligand and has a 1D chain structure bound by hydrogen bonding via ─COOH groups. Sn(H-1,2,4-BTC) contains an isomeric ligand, benzene-1,2,4-tricarboxylate, and contains inorganic chains in a layered structure held by hydrogen bonding. Sn2 (DOBDC), where DOBDC is 2,5-dioxido-benzene-1,4-dicarboxylate, is a new polymorph for this composition and has a three-dimensionally connected structure where both carboxylate and oxido groups bind to the tin centers to create a dense network with dimers of tin. In all materials, the Sn centers are found in highly asymmetric coordination, as expected for Sn(II). For all materials phase purity of the bulk is confirmed using powder X-ray diffraction, thermogravimetric analysis, and infrared spectroscopy.

Photophysical properties of tetrabutylammonium metal chlorides with different inorganic frameworks

The luminescence of single crystals of (TBA)PbCl₃, (TBA)₂Sb₂Cl₈, (TBA)₃Bi₂Cl₉ and (TBA)SnCl₅·2EtOH (TBA = tetrabutylammonium, EtOH = Ethanol) synthsized were assigned distinctively to the centres of self-trapped excitons (STEs), TBA⁺, TBA⁺ and co-emission of STEs and TBA⁺. This work demonstrates that organic cations without benzene or aromatic rings can also be used as the sole luminescence centres for metal halides.

Halogen regulation triggers structural transformation from centrosymmetric to noncentrosymmetric switches in tin phosphate halides Sn2PO4X (X = F, Cl)

A tin phosphate halide, centrosymmetric Sn2PO4F, was successfully transformed into noncentrosymmetric Sn2PO4Cl with excellent comprehensive performance by the substitution of F− with Cl−.

Double-Walled Metal-Organic Framework with Regulable Pore Environments for Efficient Removal of Radioactive Cesium Cations

An anion double-walled metal-organic framework [Co₂Li₄(BTC)₃(DMF)(H₂O)·(CH₃)₂N]_n (1) based on heterobimetallic Li⁺ and Co²⁺ ions was successfully constructed. Utilizing selective destruction and formation of Co-O/Co-N bonds in the metal chains, [Co₂Li₄(BTC)₃(py)(H₂O)·(CH₃)₂N]_n (2) and [Co₂Li₄(BTC)₃(pi)(H₂O)·(CH₃)₂N]_n (3) with the same skeleton but distinct pore structures can be surprisingly obtained. Additionally, compounds 2 and 3 can be transformed into [Co₂Li₄(BTC)₃(H₂O)₂·(CH₃)₂N]_n (4) by soaking them in an ethanol solution. This kind of single-crystal-to-single-crystal transformation successfully regulates the pore structure of MOFs and enriches the diversity of the pore wall on the premise of retaining the original framework. Most impressively, compound 1 shows high adsorption capacity for Cs⁺ cations and is a good candidate to selectively accommodate Cs⁺ among the common alkali metal ions, which is future identified by single-crystal X-ray diffraction and inductively coupled plasma mass spectrometry (ICP-MS) test. Meanwhile, compound 1 can selectively adsorb methylene blue (MB) and crystal violet (CV) molecules over Rhodamine B (RMB).

Tin Chloride Sulfates A3Sn2(SO4)3-xCl1+2x (A = K, Rb, Cs; x = 0, 1) as Multifunctional Optical Materials

The series of alkali-metal tin chloride sulfates A₃Sn₂(SO₄)_3-xCl_1+2x (A = K, Rb, Cs; x = 0, 1), K₃Sn₂(SO₄)₃Cl, Rb₃Sn₂(SO₄)₂Cl₃, and Cs₃Sn₂(SO₄)₂Cl₃, were successfully synthesized through an improved mild hydrothermal method. Interestingly, in addition to the cation size effect, the structure-directing effect of anions induces different symmetries in the three title compounds, with K₃Sn₂(SO₄)₃Cl being noncentrosymmetric, while Rb₃Sn₂(SO₄)₂Cl₃ and Cs₃Sn₂(SO₄)₂Cl₃ are centrosymmetric. Powder second-harmonic generation (SHG) measurements indicate that K₃Sn₂(SO₄)₃Cl is a nonlinear optical material that is type I phase matchable with a weak SHG response (0.1× KDP). Photoluminescence tests reveal that the three title compounds emit strong greenish yellow, orange, and salmon light, respectively, under UV excitation, indicating that they are promising inorganic solid fluorescent materials. Simultaneously, a detailed structural analysis of all the known tin(II) halide sulfates has been performed, which will guide the systematic exploration of high-performance tin(II)-based functional materials in the future.

Synthesis and photoluminescence of three bismuth(III)-organic compounds bearing heterocyclic N-donor ligands

Three bismuth(iii)-organic compounds, [Bi4Cl8(PDC)2(phen)4]·2MeCN (1), [BiCl3(phen)2] (2), and [Bi2Cl6(terpy)2] (3), were prepared from solvothermal reactions of bismuth chloride, 2,6-pyridinedicarboxylic acid (H2PDC), and 1,10-phenanthroline (phen) or 2,2';6',2''-terpyridine (terpy). The structures were determined through single crystal X-ray diffraction and the compounds were further characterized via powder X-ray diffraction, Raman and infrared spectroscopy, and thermogravimetric analysis. The photoluminescence properties of the solid-state materials were assessed using steady state and time-dependent techniques to obtain excitation and emission profiles as well as lifetimes. The compounds exhibit visible emission ranging from the yellow-green to orange region upon UV excitation. Theoretical quantum mechanical calculations aimed at elucidating the observed emissive behavior show that the transitions can be assigned as predominantly ligand-to-ligand and ligand-to-metal charge transfer transitions. The solid-state structural chemistry, spectroscopic properties, and luminescence behavior of the bismuth compounds are presented herein.