Solution and solid-state photoluminescence of bis{succinatobis[2,6-bis(2-benzimidazolyl)] lead(II)}: A comment on the lone-pair stereochemistry and its effect on supramolecular interaction

Desolvation-Degree-Induced Structural Dynamics in a Rigid Cerium-Organic Framework Exhibiting Tandem Purification of Ethylene from Acetylene and Ethane

Due to the industrial requirements for high production and high quality of ethylene, efficient purification of ethylene from acetylene and ethane is of prime importance but challenging. Dynamic metal-organic frameworks (MOFs) have demonstrated intriguing structural dynamics and diverse applications recently. Among them, although a few flexible ones have exhibited interesting ethylene purification capability, rigid ones were yet barely investigated for such purpose. In this regard, a cerium(III)-based MOF was solvothermally synthesized, which is rigid and assembled from rod molecular building blocks associated with coordinative N,N-dimethylformamide (DMF) molecules. After liberating different degrees of DMF ligands via heating under vacuum or acetone exchange, both partially desolvated compounds of Ce-MOF-1 and Ce-MOF-2 were concertedly isolated in a fashion of single-crystal to single-crystal transformation. Although both newly generated materials crystallize in the same space group, they exhibit dissimilar unit cell parameters and slightly distinct ultramicropore sizes and pore microenvironments, thanks to the discrepancy in the desolvation degree. Consequently, Ce-MOF-1 and Ce-MOF-2 individually demonstrate C₂H₂- and C₂H₆-selective adsorption behavior, resulting in the potential tandem separation of C₂H₄ from C₂H₂ and C₂H₆ mixtures. The above results were successfully supported by not only single gas adsorption isotherms but also grand canonical Monte Carlo (GCMC) calculation studies and dynamic breakthrough experiments. The present work may pave the way for rigid MOFs aiming at advancing applications via solid-state structural dynamics.

Multifunctional Zr-MOF Based on Bisimidazole Tetracarboxylic Acid for pH Sensing and Photoreduction of Cr(VI)

Herein, a new luminescent zirconium MOF [Zr-BBI, BBI = 4,4',4″,4‴-(1,4-phenylenebis(1H-imidazole-2,4,5-triyl))tetrabenzoic acid] was successfully constructed by a rationally designed functionalized bisimidazole tetracarboxylic acid ligand. Zr-BBI consists of eight-connected Zr₆ clusters and four-connected BBI ligands. The high connection mode must be responsible for the high stabilities of Zr-BBI in both acidic and basic systems. Apart from the high stability, the inherent bisimidazole units endow Zr-BBI with the traits of intense fluorescent emission as well as the protonation/deprotonation behavior. Therefore, Zr-BBI could display a highly sensitive fluorescence response along with the varying pH values in the aqueous solutions and act as a pH sensing scaffold, especially in the pH value range from 4.6 to 7.12. Zr-BBI also shows good fluorescence detection performance toward Cr₂O₇^2- at a low concentration with a high K_SV value up to 6.49 × 10⁴ M^-1. Moreover, by the utilization of Zr-BBI as a catalyst, Cr(VI) could be effectively photoreduced to Cr(III) in aqueous solution under visible light irradiation, in which the introduction of a hole scavenger (benzyl alcohol) could further significantly enhance the photocatalytic efficiency. Compared to that of the recently representative MOFs, the k value of the photocatalytic reaction over Zr-BBI is as high as 0.073 min^-1. With the consideration of the presented results, Zr-BBI can serve as a multifunctional platform for efficiently sensing and photoreducing Cr₂O₇^2- in an aqueous system, which fully illustrates the feasibility that introducing specific functional groups in the framework of MOFs would enhance the related photocatalytic activity.

Onge PBJ, Binder JF, Suter R, Burford N, Macdonald CLB. 2,6-Bis(benzimidazol-2-yl)pyridine complexes of group 14 elements

Variants of the 2,6-bis(benzimidazol-2-yl)pyridine ligand are used to synthesize novel group 14 complexes of germanium and tin. The salts are characterized by X-ray crystallography, NMR, UV-vis, and the Lewis acidity of some examples are probed.

2,6-Bis(benzimidazol-2-yl)pyridines as more electron-rich and sterically accessible alternatives to 2,6-bis(imino)pyridine for group 13 coordination chemistry

2,6-bis(benzimidazol-2-yl)pyridines are more electron-rich yet more sterically open ligands for monovalent and trivalent group 13 elements than bis(imino)pyridines.

Synthesis and crystal structure of catena-poly[(μ2-nicotinato-κ2 O,O′: κ1 N)-(nitrato-κ1 O)-(bis(2-benzimidazol-ylmethyl)amine-κ3 N,N′,N′′)lead(II)], C22H18N7O5Pb

C22H18N7O5Pb, triclinic, P1̅ (no. 2), a = 7.7446(17) Å, b = 16.914(3) Å, c = 17.726(3) Å, α = 72.451(6)°, β = 86.900(6)°, γ = 88.098(7)°, V = 2210.3(7) Å3, Z = 4, R gt(F) = 0.0379, wR ref(F 2) = 0.0751, T = 153 K.

Control of metal ion size-based selectivity through chelate ring geometry. metal ion complexing properties of 2,2'-biimidazole

Some metal ion complexing properties of 2,2'-biimidazole (BIM) are presented. The ligand BIM forms minimum steric strain complexes with hypothetical metal ions with M-N (metal-nitrogen) bond lengths of 4.2 A, in contrast to more usual ligands such as bipy (2,2'-bipyridyl) that prefer metal ions with M-N bond lengths of 2.51 A. This metal ion size-based preference of BIM suggests that ligands with such architecture could be used to produce selectivity (differences in log K(1)) for very large metal ions. To test this hypothesis, the crystal structure of [Pb(BIM)(2)(ClO(4))(2)](2) (1) was determined as the first example of a complex of BIM with a large metal ion. In addition, formation constants (log K(1)) for BIM with metal ions ranging from the very small Cu(II) to the very large Ba(II) ion were determined to examine the effect of the architecture of BIM on metal ion selectivity. The structure of 1 gave: Triclinic, P1, a = 8.314(2) A, b = 8.677(2) A, c = 14.181(3) (A), alpha = 91.143(3) degrees , beta = 104.066(2) degrees , gamma = 106.044(3) degrees , V = 949.5(4) A(3), Z = 1, R = 0.030. Pb(II) in 1 is eight-coordinate, with relatively short Pb-N bonds to the two BIM ligands ranging from 2.366(5) to 2.665(5) A, while the four Pb-O bonds are very long at 2.826(5) to 3.123(5) A. This is typical of the structure of Pb(II) complexes that have a stereochemically active lone pair of electrons, which is postulated to be situated in the vicinity of the long Pb-O bonds. The geometry of the chelate rings formed by BIM with Pb(II) in 1 is analyzed, and it is shown that these are closer in structure to the minimum-strain chelate ring formed by BIM with a very large metal ion than is the case for structures reported in the literature with smaller metal ions. The formation constants (log K(1)) determined for BIM at 25 degrees C in 0.1 M NaClO(4) by UV-visible spectroscopy are as follows: Cu(II), 6.35; Ni(II), 4.89; Zn(II), 3.42; Cd(II), 3.86; Ca(II), -0.2; Pb(II), 3.2; Ba(II), 0.2. The log K(1) values for BIM complexes show that, as expected from the geometry of the chelate ring formed by BIM, the complexes of BIM with small metal ions such as Cu(II) are considerably weaker than with ligands such as bipy, where the ligand architecture is more favorable for forming chelate rings with small metal ions. In contrast, for very large metal ions such as Pb(II) or Ba(II), the log K(1) values for BIM complexes are larger than for bipy. The use of ligand architecture in BIM-type ligands to engineer selectivity for very large metal ions is discussed. Some fluorescence results for BIM and its complexes are presented. BIM itself fluoresces very strongly, while all of its complexes except for Ca(II) show diminished fluorescence intensity, ranging from small shifts and decreases for Ba(II) to very large decreases for Cd(II), which may be due to the distortion of the ligand geometry in its complexes by metal ions that are too small for low-strain coordination with BIM.

Poly[mu(8)-4,4'-bipyridine-2,2',6,6'-tetracarboxylato-dilead(II)]

The Pb(II) cation in the title compound, [Pb(2)(C(14)H(4)N(2)O(8))](n), is seven-coordinated by one N atom and six O atoms from four 4,4'-bipyridine-2,2',6,6'-tetracarboxylate (BPTCA(4-)) ligands. The geometric centre of the BPTCA(4-) anion lies on an inversion centre. Each pyridine-2,6-dicarboxylate moiety of the BPTCA(4-) ligand links four Pb(II) cations via its pyridyl N atom and two carboxylate groups to form two-dimensional sheets. The centrosymmetric BPTCA(4-) ligand then acts as a linker between the sheets, which results in a three-dimensional metal-organic framework.

μ-Adipato-κO:O-bis-{[2,6-bis-(1H-benzimidazol-2-yl-κN)pyridine-κN](nitrato-κO)lead(II)}

The dinuclear title compound, [Pb₂(C₆H₈O₄)(NO₃)₂(C₁₉H₁₃N₅)₂], lies with the mid-point of the butyl chain of the bridging adipate unit on a center of inversion. The Pb^II ion is covalently bonded to the nitrate anion and is bonded to a carboxyl­ate group of the adipate unit by another covalent bond. The N-heterocycle functions in a chelating tridentate mode. The metal atom exists in a Ψ-octa­hedral coordination environment. When weaker Pb⋯O inter­actions are also considered, the geometry is a Ψ-tricapped trigonal prism in which the lone-pair electrons occupy one face of the trigonal prism. Adjacent mol­ecules are linked into a layer structure by N—H⋯O hydrogen bonds.