Photochromism of a 3D Cd^II Complex with Two Captured Ligand Isomers Generated In Situ from the Same Precursor

Abstract

Photochromic compounds have gained intense interest owing to their novel photochemical and photophysical reactions as well as their various potential applications such as in sunglasses and optical memories.[1] An appreciable number of photochromic families have been reported to date; [2] however, those based on an electron-transfer (redox) chemical process, especially for metal-organic compounds, are rare.[3] We present herein a hydrothermally synthesized 3D complex [Cd 2 (ic)(mc)(4,4'-bipy) 3 ] n ·4n H 2 O (1Y; ic= itaconate, mc = mesaconate) which exhibits reversible radicalbased redox photochromic behavior. This compound also merits attention for its unusual five-connected Archimedeantype topological structure and unexpected "capture" of isomeric ic and mc ligands that are generated in situ from trans-propene-1,2,3-tricarboxylic acid (H 3 L, Scheme 1).Yellow prismatic crystals of 1Y accompanied by a few colorless block crystals of [Cd 3 L 2 (H 2 O) 6 ] n (2; Figure S1 in the Supporting Information) were obtained by the hydrothermal reaction of CdCO 3 , 4,4'-bipy, H 3 L, and deionized water in a molar ratio of 1:1:1:1111 at 120 8C for 12 h. Powder X-ray diffraction (PXRD) verified the purity of a mechanically separated sample of 1Y ( Figure S2 in the Supporting Information). Thermal analysis and PXRD data show that compound 1Y still keeps its metal-organic framework at 200 8C after the elimination of lattice water molecules ( Figure S2 and S3 in the Supporting Information).A single-crystal X-ray diffraction study of 1Y revealed a 3D structure based on a network of seven-coordinated Cd II centers linked by three kinds of bridging ligands. As shown in Figure 1, the central Cd1 atom is located in a pentagonalbipyramidal coordination environment with N41 and N42 atoms of crystallographically independent 4,4'-bipy ligands acting as the two pyramidal apexes. An important feature of 1Y is the simultaneous "capture" of isomeric ic and mc ligands that originate from the in situ pyrolysis of H 3 L. [4]

Hydrothermal syntheses, crystal structures, and photocatalytic properties of two Co(II) complexes with the flexible citraconic acid

“…The designs and selections of O‐donor and N‐donor ligands are important to the synthesis of coordination polymers with fascinating structures and excellent performances . Small aliphatic carboxylates are widely used as O‐donor ligands to obtain a number of coordination polymers not only for their low prices and good flexibilities, but also for their diverse coordination modes . Some time ago, we obtained several coordination polymers based on a flexible itaconic acid .…”

“…Some time ago, we obtained several coordination polymers based on a flexible itaconic acid . However, there are relatively few reports on the syntheses of transition metal coordination polymers by using citraconic acid as a O‐donor ligand, which is an isomer of itaconic acid . In addition, the imidazolyl ligand is one of the most common N‐donor ligands to adjust the structures of coordination polymers in light of their different molecule sizes and flexibilities to satisfy the requirement of coordination geometries of metal ions in the assembly process …”

A new CdII coordination polymer with a self-penetrating architecture induced by the molecular conformation of a rigid bithiophene ligand

“…Self-penetrating architectures (Cao et al, 2012;Yang et al, 2010;Carlucci et al, 2003;Tong et al, 2003), wherein the shortest circuits are penetrated by other rings within a single net, is an important issue regarding entangled systems ( Fig. 1) due to their structural complexity and functional properties (Martins et al, 2017;Gong et al, 2016;Shi et al, 2014;Yang et al, 2009Yang et al, , 2014Wu et al, 2011;Wang et al, 2007Wang et al, , 2008Liao et al, 2006). The favourite strategy for this issue is the use of conformationally kinked flexible ligands (Xu et al, 2015;Kim et al, 2014;Zhou et al, 2012;Wang et al, 2011;Hou et al, 2010).…”

Ultrasound and solvent-induced reversible chromism in a luminescent chalcogenidostannate

“…When given stimulus, such as light, solvent, temperature, and pH, materials may exhibit photochromism, solvatochromism, thermochromism, electrochromism, mechanochromism, vapor-chromism, etc. [2][3][4][5][6][7][8][9][10][11]. Chromism may occur when, among solid compounds, changes of the geometrical or electronical structure take place, which affect the physicochemical properties [12].…”