Synthesis and Structure of Binary Copper/Silver–Arsenic Clusters Derived from Zintl Ion As 7 3–

Covalent Organic Frameworks-Based Electrochemical Sensors for Food Safety Analysis

Food safety is a key issue in promoting human health and sustaining life. Food analysis is essential to prevent food components or contaminants causing foodborne-related illnesses to consumers. Electrochemical sensors have become a desirable method for food safety analysis due to their simple, accurate and rapid response. The low sensitivity and poor selectivity of electrochemical sensors working in complex food sample matrices can be overcome by coupling them with covalent organic frameworks (COFs). COFs are a kind of novel porous organic polymer formed by light elements, such as C, H, N and B, via covalent bonds. This review focuses on the recent progress in COF-based electrochemical sensors for food safety analysis. Firstly, the synthesis methods of COFs are summarized. Then, a discussion of the strategies is given to improve the electrochemistry performance of COFs. There follows a summary of the recently developed COF-based electrochemical sensors for the determination of food contaminants, including bisphenols, antibiotics, pesticides, heavy metal ions, fungal toxin and bacterium. Finally, the challenges and the future directions in this field are discussed.

Synthesis and Characterization of Ternary Clusters Containing the [As16]10- Anion, [MM'As16]4- (M = Nb or Ta; M' = Cu or Ag)

The [Nb@As₈]^3- anion was first isolated from solution in 1986, and a number of isostructural [M@Pn₈]^n- clusters (M = Nb, Cr, or Mo; Pn = As or Sb; n = 2 or 3) have since been reported. We show here how anions of this class can be used as synthetic precursors that, in combination with sources of low-valent late transition metals (Cu and Ag), generate ternary polyarsenide cluster anions with unprecedented structural motifs. Chain type [MM'As₁₆]^4- (M = Nb or Ta; M' = Cu or Ag) units are found in compounds 2-5. These clusters contain a nortricyclane-like As₇ cage and a [M@As₈] crown, linked by a single As atom, and represent a fusion of two quite distinct branches of polyarsenide chemistry. Our analysis of the electronic structure confirms that the cluster retains many of the features of the component units. Electrospray ionization mass spectrometry reveals a series of smaller component ions containing 8-12 As atoms, the density functional theory-computed structures of which can be understood in terms of the pseudoelement concept. This work not only presents a new type of coordination mode for As clusters but also offers a point of entry for the rational design of multinary arsenic-based materials.

Occurrence of Double Bond in π-Aromatic Rings: An Easy Way to Design Doubly Aromatic Carbon-Metal Structures

A chemical bonding of several metallabenzenes and metallabenzynes was studied via an adaptive natural density partitioning (AdNDP) algorithm and the induced magnetic field analysis. A unique chemical bonding pattern was discovered where the M=C (M: Os, Re) double bond coexists with the delocalized 6c-2e π-bonding elements responsible for aromatic properties of the investigated complexes. In opposition to the previous description where 8 delocalized π-electrons were reported in metallabenzenes and metallabenzynes, we showed that only six delocalized π-electrons are present in those molecules. Thus, there is no deviation from Hückel's aromaticity rule for metallabenzynes/metallabenzenes complexes. Based on the discovered bonding pattern, we propose two thermodynamically stable novel molecules that possess not only π-delocalization but also retain six σ-delocalized electrons, rendering them as doubly aromatic species. As a result, our investigation gives a new direction for the search for carbon-metal doubly aromatic molecules.