Heteroleptic palladium(II) complexes of dipyrrin-1,9-dione supported by intramolecular hydrogen bonding
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The dipyrrin-1,9-dione framework, which is characteristic of the propentdyopent pigments deriving from heme metabolism, coordinates metal ions as monoanionic bidentate donors. The resulting analogs of dipyrrinato complexes undergo reversible ligand-based reductions, thus showcasing the ability of the dipyrrindione scaffold to act as an electron reservoir. Herein we report the synthesis and characterization of three heteroleptic palladium complexes of the redox-active dipyrrindione ligand. Primary amines were chosen as additional ligands so as to assemble complexes of planar geometries with complementary interligand hydrogen-bonding. Full chemical characterization confirms the hydrogen bonding interactions between the primary amine ligands and the acceptor carbonyl groups on the dipyrrolic ligand. The resulting heteroleptic compounds display reversible one-electron reduction events that are centered on the dipyrrindione ligand as revealed by voltammetry and spectroelectrochemistry data. Within these planar Pd(II) complexes, the propentdyopent motif therefore combines reversible ligand-based redox chemistry with interligand hydrogen bonding in the primary coordination sphere of the metal center.Keywords:
Non-innocent ligand
Coordination complex
Abstract Metal‐ versus ligand‐centered redox processes and the effects of substituents on the ligands on the spectroscopic properties of the metal complexes are at the heart of research on metal complexes with non‐innocent ligands. This work presents three examples of chromium complexes that contain both oxido and corrolato ligands, with the substituents on the corrolato ligands being different in the three cases. Combined X‐ray crystallographic, electrochemical, UV/Vis/NIR/EPR spectroelectrochemical, and EXAFS/XANES measurements, together with DFT calculations, have been used to probe the complexes in three different redox forms. This combined approach makes it possible to address questions related to chromium‐ versus corrolato‐centered redox processes, and the accessibility (or not) of Cr IV , Cr V , and Cr VI in these complexes, as well as their spin states. To the best of our knowledge, these are the first EXAFS/XANES investigations on Cr‐corrolato complexes in different redox forms, and hence these data should set benchmarks for future investigations on such complexes by this method.
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XANES
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AbstractThe synthesis, redox and spectral properties of a Co(II) 3D coordination framework, consisting of interpenetrated 2D (4,4′)-nets with the redox-active tris(4-(pyridine-4-yl)phenyl)amine (NPy3) ligand is reported. The accessible redox states in the framework were explored through solid state electrochemical and spectroelectrochemical experiments. The incorporation of a redox-active metal in conjunction with a redox-active ligand provides access to a greater number of accessible redox states within a solid state material. This strategy holds promise for the synthesis of multifunctional materials that are capable of changing their properties as a function of the electronic state.Keywords:: redox-activeMetal-Organic Frameworkselectrochemistry AcknowledgementsWe gratefully acknowledge support from the Australian Research Council. The solid state crystal structure data were obtained on the MX2 beamline at the Australian Synchrotron, Victoria, Australia. We thank Dr Thomas Faust, Mr Marcello Solomon and Dr Peter Turner for assistance in obtaining the X-ray data.Disclosure statementNo potential conflict of interest was reported by the authors.
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Abstract The linear octadentate ligand 3,4,3‐LICAM(C) ( 2 ) is one of the most effective chelating agents for Pu IV that is not acutely toxic; however, at physiological pH, due to the weak acidity of the catechol hydroxy groups and the large proton dependence of the complexation reaction, only three of the four catecholate subunits are coordinated to Pu IV . To overcome this disadvantage, a new topological class of octadentate ligands based on tetrapodal amine backbones and 2,3‐dihydroxyterephthalamide ( 3 ) (TAM) binding units were designed and synthesized. The amide substituents provide a handle by which the functionality of the ligand can be readily modified, and this synthetic strategy and procedure can be extended to prepare a variety of new multidentate metal‐coordination and extraction agents. A streamlined synthesis for the terephthalamides, both symmetric and asymmetric, was recently reported. In this work, the synthetic details of their incorporation into octadentate systems for use as coordination or extraction agents for Pu IV or other metals in the +4 oxidation state are described. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
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In the monomeric title complex, [Co(C6H8O4)(C10H9N3)(H2O)2]·3H2O, the distorted octa-hedral CoN2O4 coordination environment comprises two N-atom donors from the bidentate di-pyridyldi-amine ligand, two O-atom donors from one of the carboxyl-ate groups of the bidentate chelating adipate ligand and two water mol-ecules. In addition, there are three solvent water mol-ecules which are involved in both intra- and inter-unit O-H⋯O hydrogen-bonding inter-actions, which together with an amine-water N-H⋯O hydrogen bond produce a three-dimensional framework.
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Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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Redox‐active ligands lead to ambiguity in often clearly defined oxidation states of both the metal center and the ligand. The arylazothioformamide (ATF) ligand class represents a redox‐active ligand with three possible redox states (neutral, singly reduced, and doubly reduced). ATF–metal interactions result in strong colorimetric transitions allowing for the use of ATFs in metal detection and/or separations. While previous reports have discussed dissolution of zerovalent metals, the resulting oxidation states of coordination complexes have proved difficult to interpret through X‐ray crystallographic analysis alone. This report describes the X‐ray crystallographic analysis combined with computational modeling of the ATF ligand and metal complexes to deconvolute the metal and ligand oxidation state of ATF–metal complexes. Metal(ATF) 2 complexes that originated from zerovalent metals were found to exist as dicationic metal centers containing two singly reduced ATF ligands. When employing Cu I salts instead of Cu 0 to generate ATF–copper complexes, the Cu I in the resulting complexes remained in its oxidation state, and the ATF ligand remained “innocent”, existing in its neutral state. Although the use of CuX (X = Br or I) or [Cu(NCMe) 4 ]Y (Y = BF 4 or PF 6 ) generated species of the type: [(ATF)Cu(µ‐X)] 2 and [Cu(ATF) 2 ]Y, respectively, the ATF ligand remained in its neutral state for each species type.
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Metal aquo complex
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A bipyridyl-based anion receptor is utilized as a ligand in a tetrahedral FeCl2 complex and demonstrates secondary coordination sphere influence through intramolecular hydrogen bonding to the chloride ligands as evidenced by X-ray crystallography.
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