Crystal structures of an imidazo[1,5-a]pyridinium-based ligand and its (C13H12N3)2[CdI4] hybrid salt

Stabilized photoemission from organic molecules in zero-dimensional hybrid Zn and Cd halides

This work explores the utilization of a photoactive organic cation for the preparation of R2MCl4 (M = Zn, Cd; R = (E)-4-styrylpyridinium, C13H12N+).

Organic-inorganic hybrid tetrachlorocadmates as promising fluorescent agents for cross-linked polyurethanes: synthesis, crystal structures and extended performance analysis

The aim of this work is to apply organic–inorganic hybrid salts made of imidazo[1,5-a]pyridinium-based cations and halometallate anions as fluorescent agents to modify cross-linked polyurethane (CPU) for the creation of flexible photoluminescent films. The use of ionic compounds ensures excellent dispersion of the luminescent components in the polymer matrix and prevents solid-state quenching. The absence of phase segregation makes it possible to fabricate uniformly luminescent films with a large area. To this, new tetrachlorocadmate salts [L]₂[CdCl₄] (1) and [L′]₂[CdCl₄] (2), where L⁺ is 2-methyl-3-(pyridin-2-yl)imidazo[1,5-a]pyridinium and [L′]⁺ is 2-methylimidazo[1,5-a]pyridinium cations, have been prepared and characterized by IR, NMR, UV-Vis spectroscopy and single crystal X-ray diffraction. The organic cations resulted from the oxidative cyclization-condensation involving CH₃NH₂·HCl and 2-pyridinecarbaldehyde in methanol (1), and formaldehyde, CH₃NH₂·HCl and 2-pyridinecarbaldehyde in an aqueous media (2). In the crystal of 1, loosely packed tetrahedral cations and π–π stacked anions are arranged in separate columns parallel to the a-axis. The pseudo-layered structure of 2 is built of the organic and inorganic layers alternating along the a axis. The adjacent CdCl₄²⁻ anions in the inorganic layer show no connectivity. The organic–inorganic hybrids 1 and 2 were immobilized in situ in the cross-linked polyurethane in low content (1 wt%). The photoluminescent properties of 1 and 2 in the solid state and in the polymer films were investigated. The semi-transparent CPU films, that remain stable for months, retain the photoluminescent ability of both hybrids in the blue region with a prominent red shift in their emission.

Hybrid salts made of imidazo[1,5-a]pyridinium-based cations with easily tunable electronic structures, and halometallate anions that do not include any rare-earth or noble metals were used to fabricate flexible luminescent CPU films.

Crystal structure and characterization of a new copper(II) chloride dimer with methyl(pyridin-2-ylmethylidene)amine

The new copper(II) complex [CuLCl₂]₂, where L is a product of Schiff base condensation between methyl­amine and 2-pyridine­carbaldehyde, is built of discrete centrosymmetric dimers.

The new copper(II) complex, namely, di-μ-chlorido-bis­{chlorido­[meth­yl(pyri­din-2-yl­methyl­idene)amine-κ²N,N′]copper(II)}, [Cu₂Cl₄(C₇H₈N₂)₂], (I), with the ligand 2-pyridyl­methyl-N-methyl­imine (L, a product of Schiff base condensation between methyl­amine and 2-pyridine­carbaldehyde) is built of discrete centrosymmetric dimers. The coordination about the Cu^II ion can be described as distorted square pyramidal. The base of the pyramid consists of two nitro­gen atoms from the bidentate chelate L [Cu—N = 2.0241 (9), 2.0374 (8) Å] and two chlorine atoms [Cu—Cl = 2.2500 (3), 2.2835 (3) Å]. The apical position is occupied by another Cl atom with the apical bond being significantly elongated at 2.6112 (3) Å. The trans angles of the base are 155.16 (3) and 173.79 (2)°. The Cu⋯Cu separation in the dimer is 3.4346 (3) Å. In the crystal structure, the loosely packed dimers are arranged in stacks propagating along the a axis. The X-band polycrystalline 77 K EPR spectrum of (I) demonstrates a typical axial pattern characteristic of mononuclear Cu^II complexes. Compound (I) is redox active and shows a cyclic voltammetric response with E_1/2 = −0.037 V versus silver–silver chloride electrode (SSCE) assignable to the reduction peak of Cu^II/Cu^I in methanol as solvent.

Crystal structure of imidazo[1,5-a]pyridinium-based hybrid salt (C13H12N3)2[MnCl4]

A new organic-inorganic hybrid salt [L]2[MnCl4] (I) where L + is the 2-methyl-3-(pyridin-2-yl)imidazo[1,5-a]pyridinium cation, is built of discrete organic cations and tetra-chlorido-manganate(II) anions. The L + cation was formed in situ in the oxidative cyclo-condensation of 2-pyridine-carbaldehyde and CH3NH2·HCl in methanol. The structure was refined as a two-component twin using PLATON (Spek, 2020 ▸) to de-twin the data. The twin law (-1 0 0 0 - 1 0 0.5 0 1) was applied in the refinement where the twin component fraction refined to 0.155 (1). The compound crystallizes in the space group P21/c with two crystallographically non-equivalent cations in the asymmetric unit, which possess similar structural conformations. The fused pyridinium and imidazolium rings of the cations are virtually coplanar [dihedral angles are 0.89 (18) and 0.78 (17)°]; the pendant pyridyl rings are twisted by 36.83 (14) and 36.14 (13)° with respect to the planes of the remaining atoms of the cations. The tetra-hedral MnCl4 2- anion is slightly distorted with the Mn-Cl distances falling in the range 2.3469 (10)-2.3941 (9) Å. The distortion value of 0.044 relative to the ideal tetra-hedron was obtained by continuous shape measurement (CShM) analysis. In the crystal, the cations and anions form separate stacks propagating along the a-axis direction. The organic cations display weak π-π stacking. The anions, which are stacked identically one above the other, demonstrate loose packing; the minimum Mn⋯Mn separation in the cation stack is approximately 7.49 Å. The investigation of the fluorescent properties of a powdered sample of (I) showed no emission. X-band EPR data for (I) at 293 and 77 K revealed broad fine structure signals, indicating moderate zero-field splitting.