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Functional Nanoceramics A Brief Review on Structure Property Evolutions of Advanced Functional Ceramics Processed Using Microwave and Conventional Techniques
Published in Sivashankar Krishnamoorthy, Krzysztof Iniewski, Nanomaterials, 2017
Santiranjan Shannigrahi, Mohit Sharma
It is now obvious that in the majority of the functional materials, several different elements form a molecule, where the electronic structure of this cluster is very different from any of its original elemental configurations because of the transfer and/ or sharing of valence electrons among atoms. In general, only the valence electrons are most critical to bonding; the distribution and motion of valence electrons are usually described by the molecular orbitals. These valence states and molecular orbits are responsible for the functional properties of the molecule. The ligand field theory is designed to describe the molecular structure of an atom cluster. When different elements are combined to form a crystalline solid in which the atoms or atom groups (or molecules) are bonded together to form a three-dimensional structure with specified symmetries, the properties of the solid would depend on both the electronic structure of the atoms or atom groups and their spatial distribution. The molecular orbital theory and band structure theory are usually applied to elucidate the relationship between the structure and the properties. Based on the electron band structure, inorganic materials can be classified as conductors, semiconductors, and insulators. If a change is made in the crystal structure so that the band gap is reduced or eliminated, a transition from an insulator to a conductor is possible. Modification of a crystal structure can be performed by changing either the spatial distribution of atoms (such as bonding angles, bonding lengths, and symmetry of atom arrangement) or the chemical composition (such as from stoichiometry to nonstoichiometry). All these changes are referred to as structural evolution, which is closely related to the properties of the materials. Many functional properties of inorganic materials are determined by the elements with mixed valences in the structure unit, by which we mean that an element has two or more different valences while forming a compound. Valence mixture refers to a case in which several elements have different valences, but each one only has a single valence. In the periodic table of fundamental elements, 40 elements can form mixed valence compounds; transition d-block elements and lanthanide (Eu, Yb, Ce, Pr, Tb, etc.) are typical examples. Modern inorganic chemistry has shown that the oxidation state of any element can be modified under special conditions. Many oxide functional materials contain elements with mixed valences. This is a typical difference between functional materials and structural materials. The concept of mixed valence chemistry offers a pathway to design and synthesize new compounds with unique optical, electric, or magnetic properties. Research in functional materials in its broad sense always depends on the conception and synthesis of interesting novel mixed-valence compounds. The discovery of high-temperature superconductor compounds is a fascinating successful example of the mixed valence chemistry. We believe that exploring the possible structures of mixed valence compounds and their evolution behaviors may lead to many pathways to synthesize new functional materials.
Structural characterization of ((9-fluorenylidene) (ferrocenyl)methyl)palladium iodide as the catalytic intermediate in the synthesis of 9-(ferrocenyl (ferrocenylethynyl)methylene)-9H-fluorene
Published in Journal of Coordination Chemistry, 2022
However, it is well known that the electrical properties of conjugated materials, such as the high conductivity of films of doped-polyacetylene, arise from inter- instead of intra-molecular charge-transfer processes [5]. The potential for similar intermolecular interactions or “cross-talk” has provoked debate around the design, synthesis and properties of “insulated” molecular wires for use in “large area” molecular junctions [6], while also inspiring studies of carefully designed molecular mixed-valence systems in which the bridge structure brings the redox sites into relatively close proximity, permitting weak through-space coupling [7]. In an interesting variation on this theme, the redox response of ferrocene-containing monolayers has been noted to be broadened or even resolved into two separate waves, consistent with the formation of a partially oxidized film with “mixed-valence” character [8].
Preparation of nano-TiO2 sensitized by new ruthenium complex for photocatalytic degradation of methylene blue under visible light irradiation
Published in Journal of Coordination Chemistry, 2022
In the last few decades, synthesis of binuclear metal complexes with a suitable bridge ligand that leads to the formation of stable mixed valence states attracts attention [19–22]. These compounds are important in biological processes [23], molecular electronics [24], and also theoretical studies of electron transfer kinetics [25]. The presence of the pyrazine ligand in the Creutz–Taube complex as a powerful bridge arose interests of researchers to design binuclear ruthenium(II) complexes with pyrazine ligands such as 2,3-bis(2-pyridyl)aminoxaline [26], 2,2′-bipyrimidine [27–30] and 2,3-bis(2-pyridyl)pyrazine [31, 32]. Homo- or hetero-polynuclear ruthenium complexes are well synthesized with tppz and π-acidic (e.g. 2,2′-bipyridine, 2,2′,6′,2ʺ-terpyridine) and σ-donor (monodentate amines) are most used as the terminal ligands [33]. The UV-vis spectrum of all these compounds shows there is an acceptable absorption in the visible region. This absorption is related to the Ru [d(π)]-tppz(π*) MLCT transition. This encouraged us to design and synthesize a complex containing tppz and a terminal bipyridine ligand with a carboxylic substituent that can attach to the nano-TiO2 surface and provide a dye-sensitized photocatalyst.
DNA and RNA binding studies on a novel bromo-bridged dimeric copper(II) complex stabilized from a Schiff base ligand
Published in Journal of Coordination Chemistry, 2019
Naba Kr Mandal, Bhargab Guhathakurta, Pritha Basu, Ankur Bikash Pradhan, Chandra Shekhar Purohit, Shubhamoy Chowdhury, Jnan Prakash Naskar
Couple 2 is irreversible, whereas couple 1 is almost quasi-reversible in nature. The ipc/ipa value for couple 2 is 6.679 in 1. During CV experiment a mixed-valence species, Cu(III)/Cu(II), is formed in the intermediate redox step. For such type of mixed-valence species, the extent of stability can be realized electrochemically by evaluating conproportionation constant (Kcon). The conproportionation constant may be represented as: where ΔE = [E1/2(Ox2)–E1/2(Ox1)]. The greater is the stability of the mixed valence species, the higher is the value of Kcon[57, 58]. The magnitude of Kcon was found to be 3.72 × 103 by taking ΔE for 1 as 0.378 V versus SCE (after reference conversion to SCE). The stability of the mixed-valence species also depends on ligand unsaturation [59]. The redox response in 1 can be written as: