Rare-earth squarate frameworks with topology

As a typical planar 4-connected ligand that possesses D_4h symmetry, the squarate ligand is expected to construct some interesting topologies. Here, we report that the assembly of the squarate ligand with rare-earth ions can produce a series of (4, 8)-connected frameworks with the "smallest" scu type topology. Among these compounds, the Tb based analogue not only possesses a good proton conductivity, but also exhibits luminescence responses toward MnO₄^- and Cr₂O₇^2-, making it a candidate for multifunctional materials.

Applications of Viologens in Organic and Inorganic Discoloration Materials

Viologen derived from 4,4'-bipyridine has attracted much attention because of its color changing properties with electron transfer, unique redox stability and structural diversity. These characteristics have led to its successful use in various applications, in particular in color-changing materials. In the past few years, researchers have been working on the syntheses of viologen-based color-changing functional materials, and such materials have been widely used in many fields. In photochromic materials, it is used as anti-counterfeiting material; in thermochromic, it is used as memory storage material, and in electrochromic, it is used as a battery material. This Review discusses the progress of viologen in organic and inorganic discoloration materials in recent years. The syntheses of viologen and its derivatives are summarized, and its application in the field of discoloration materials is introduced.

Photochromic and electrochromic properties of a viologen-based multifunctional Cd-MOF

A pair of novel multifunctional MOF materials [Cd₂(L)₂(D/L-Lm)(H₂O)₂]·5H₂O (denoted as D/L-Cd-MOF) has been synthesized by combining the viologen-functionalized ligand H₂L⁺Cl^- and chiral D/L-tartaric acid (H₂Lm) with a simple solvothermal method. Due to the unique photoelectric response properties of the viologen units, reversible photochromic and electrochromic properties have been combined in D/L-Cd-MOF, which points to a new way of designing and constructing multifunctional photoelectric materials.

Photo-sensitive hybrids constructed from diphenyliodonium and metal-thiocyanates: photo-induced structure and property transformations

New hybrids constructed from diphenyliodonium and metal thiocyanates have been prepared, and their photo-induced structural transformations and corresponding color/fluorescence/magnetism variations have been investigated.

Mixed-Ligand Uranyl Squarate Coordination Polymers: Structure Regulation and Redox Activity

The electron-rich squarate ion (C₄O₄^2-, SA^2-) possesses electronic delocalization over the entire molecule and good redox activity, and the functionalization of metal-organic complexes with the SA^2- group is desirable. In this work, a mixed-ligand method is used to construct novel uranyl squarate coordination polymers utilizing 4,4'-bipyridine (bpy), 4,4'-bipyridine-N,N'-dioxide (bpydo), 1,10-phenanthroline (phen), 4,4'-vinylenedipyridine (vidpy), and in situ formed oxalate (OA^2-) as ancillary ligands. Seven mixed-ligand uranyl compounds, [(UO₂)(OH)(SA)](Hbpy) (1), [(UO₂)(H₂O)(SA)₂](H₂bpy) (2), (UO₂)(H₂O)(SA)(bpydo)·2H₂O (3), (UO₂)(H₂O)(SA)(phen)·H₂O (4), (UO₂)(OH)(SA)_0.5(phen)·H₂O (5), [(UO₂)(SA)(OA)_0.5](Hphen) (6), and [(UO₂)(SA)(OA)_0.5](Hvidpy) (7), with varying crystal structures were synthesized under hydrothermal conditions. Compound 1, together with bpy molecules filling in the interlayer space as template agents, has a two-dimensional (2D) network structure, while 2 gives a one-dimensional (1D) chain based on mononuclear uranium units. Compound 3 shows a neutral 2D network through the combined linkage of SA^2- and bpydo. Both 4 and 5 have a similar chain-like structure due to the capping effect of phen motifs, while phen molecules in 6 act as templating agents after protonation. Similar to 6, compound 7 has a "sandwich-like" structure in which the Hvidpy motifs locate in the voids of layers of 2D uranyl-squarate networks. The redox properties of typical mixed-ligand uranyl-squarate compounds, 1, 4, and 5 with high phase purity, are characterized using cyclic voltammetry. All three of these uranyl coordination compounds show anode peaks (E_a) at 0.777, 0.804, and 0.760 V, respectively, which correspond to the oxidation process of SA^2- → SA. Meanwhile, cathodic peaks (E_c) at -0.328, -0.315, and -0.323 V corresponding to the reduction process of U(VI) → U(V) are also observed. The results reveal that all three of these uranyl coordination compounds show good redox activity and, most importantly, the interplay between two different redox-active motifs of SA^2- organic linker and uranyl node. This work enriches the library of redox-active uranyl compounds and provides a feasible mixed-ligand method for regulating the synthesis of functional actinide compounds.

Polymeric Terbium(III) Squarate Hydrate as a Luminescent Magnet

Polymeric terbium(III) squarate hydrate [{Tb2(C4O4)3(H2O)8}n] was prepared from TbCl3 or Tb2O3 and squaric acid. The crystal structure was determined in a monoclinic Pc space group, and the whole molecular arrangement gives a sandwiched two-dimensional structure. The coordination polyhedra are described as a square antiprism. The solid complex emits green light under UV irradiation at room temperature with the quantum yield of 25%. Although Tb3+ is a non-Kramers ion, the alternating-current magnetic susceptibility showed frequency dependence in a 2000-Oe DC field, and the effective energy barrier for magnetization reorientation was 33(2) K. Thus, [{Tb2(C4O4)3(H2O)8}n] displayed functions of a potential luminescent magnet.

A Three-Component Hybrid Templated by Asymmetric Viologen Exhibiting Visible-Light-Driven Photocatalytic Degradation on Dye Pollutant in Maritime Accident Seawater

The increasing dangerous chemical pollutants led by shipping accidents call for the new pollutant treatment strategy. In this work, a new three-component hybrid {[(BiI6)I13]·2I3·(H-BPA)4}n (1) can be used in dye degradation in seawater. The highly interesting feature of 1 lies in its unique 1-D Z-shape [(BiI6)I13]n6− infinite chain constructed from the I···I contacts between mono-nuclear (BiI6)3− anions and I133− polyiodide anions. Finally, the hydrogen bonds between [(BiI6)I13]n6− polyanions and H-BPA2+ cations contribute to the formation a quasi-3-D network. Specifically, 1 exhibits the wide absorption zone from ultraviolet to visible regions and high charge-separation efficiency, hinting its application in visible-light catalysis. As expected, 1 represents photocatalytic activity for the degradation of rhodamine B in seawater with degradation ratio of 90%, and the photocatalytic performance is stable. This work might provide new photocatalytic material for pollutant treatment in shipping accidents.

Photochromic inorganic–organic complex derived from low-cost deep eutectic solvents with tunable photocurrent responses and photocatalytic properties

A photochromic inorganic–organic complex |C₁₀H₁₀N₂|[GaF(C₂O₄)₂] derived from low-cost deep-eutectic solvents possesses tunable photocurrent responses and photocatalytic activities.

Synthesis, Structural Characterization and Ligand-Enhanced Photo-Induced Color-Changing Behavior of Two Hydrogen-Bonded Ho(III)-Squarate Supramolecular Compounds

Two coordination polymers (CPs) with chemical formulas, [Ho2(C4O4)2(C2O4)(H2O)8]·4H2O (1) and [Ho(C4O4)1.5(H2O)3] (2), (C4O42- = dianion of squaric acid, C2O42- = oxalate), have been synthesized and their structures were determined by single-crystal X-ray diffractometer (XRD). In compound 1, the coordination environment of Ho(III) ion is eight-coordinate bonded to eight oxygen atoms from two squarate, one oxalate ligands and four water molecules. The squarates and oxalates both act as bridging ligands with 1,2-bis-monodentate and bis-chelating coordination modes, respectively, connecting the Ho(III) ions to form a one-dimensional (1D) ladder-like framework. Adjacent ladders are interlinked via O-HO hydrogen bonding interaction to form a hydrogen-bonded two-dimensional (2D) layered framework and then arranged orderly in an AAA manner to construct its three-dimensional (3D) supramolecular architecture. In compound 2, the coordination geometry of Ho(III) is square-antiprismatic eight coordinate bonded to eight oxygen atoms from five squarate ligands and three water molecules. The squarates act as bridging ligands with two coordination modes, 1,2,3-trismonodentate and 1,2-bis-monodentate, connecting the Ho(III) ions to form a 2D bi-layered framework. Adjacent 2D frameworks are then parallel stacked in an AAA manner to construct its 3D supramolecular architecture. Hydrogen bonding interactions between the squarate ligands and coordinated water molecules in 1 and 2 both play important roles on the construction of their 3D supramolecular assembly. Compounds 1 and 2 both show remarkable ligand-enhanced photo-induced color-changing behavior, with their pink crystals immediately turning to yellow crystals under UV light illumination.