Unusual structural features in tetrabromocatechol-chelated dinuclear manganese(III) complex: Synthesis, electrochemistry and thermally induced valence tautomerism

2012 ◽  
Vol 24 ◽  
pp. 140-143 ◽  
Author(s):  
Anangamohan Panja
Keyword(s):  
Structural Features ◽  
Valence Tautomerism ◽  
Thermally Induced

Variable-temperature structural studies on valence tautomerism in cobalt bis(dioxolene) molecular complexes

2017 ◽  
Vol 73 (2) ◽  
pp. 304-312 ◽  
Author(s):  
Venkatesha R. Hathwar ◽  
Marian Stingaciu ◽  
Bo Richter ◽  
Jacob Overgaard ◽  
Bo B. Iversen
Keyword(s):  
Single Crystal ◽  
Variable Temperature ◽  
Molecular Complexes ◽  
Structural Studies ◽  
Coordination Environment ◽  
Valence Tautomerism ◽  
Thermally Induced ◽  
Transition Mechanism ◽  
Crystal Structural ◽  
Cobalt Coordination

A variable-temperature single-crystal structural study of five valence tautomeric cobalt molecular complexes, CoII(3,5-DBSQ)2(DBPy)2(1), CoII(3,5-DBSQ)2(DBPy)2·1.33C7H8(1S), CoII(3,5-DBSQ)2(DCPy)2·C7H8(2S), CoII(3,5-DBSQ)2(TBPy)2(3) and CoII(3,5-DBSQ)2(TCPy)2(4) (S = toluene, 3,5-DBSQ = 3,5-di-tert-butylsemiquinonate, DBPy = 3,5-dibromopyridine, DCPy = 3,5-dichloropyridine, TBPy = 3,4,5-tribromopyridine and TCPy = 3,4,5-trichloropyridine) is reported. The re-crystallization of (1S) in toluene at 277 K resulted in a concomitant formation of a solvent-free polymorph, CoII(3,5-DBSQ)2(DBPy)2(1). Thermally induced valence tautomerism (VT) is observed only in (1S), (1) and (2S) [hs-CoII(3,5-DBSQ)2L2↔ ls-CoIII(3,5-DBSQ)(3,5-DBCat)L2(hs = high spin, ls = low spin, 3,5-DBCat = 3,5-di-tert-butylcatecholate)], whereas (3) and (4) remain locked in the hs-CoII(3,5-DBSQ)2state during cooling of the sample. Multi-temperature single-crystal studies demonstrate the change in cobalt coordination environment during the VT conversion. The non-solvated compound (1) shows a sharp VT transition (T1/2∼ 245 K with ΔT∼ 10 K) from hs-CoII(3,5-DBSQ)2(DBPy)2to ls-CoIII(3,5-DBSQ)(3,5-DBCat)(DBPy)2oxidation state, whereas the other polymorph with lattice solvent (1S) results in a broad transition (T1/2∼ 150 K with ΔT∼ 100 K). This increase in the VT transition temperature for (1) relative to (1S) illustrates the effect of lattice solvent on the VT transition mechanism. Additionally, the influence of halogen substitutions on the pyridine ring is discussed with respect to observed VT behaviour in the studied compounds.

Thermally Induced and Photoinduced Valence Tautomerism in a Two-Dimensional Coordination Polymer

2011 ◽  
Vol 50 (2) ◽  
pp. 424-426 ◽  
Author(s):  
Bao Li ◽  
Li-Qin Chen ◽  
Rong-Jia Wei ◽  
Jun Tao ◽  
Rong-Bin Huang ◽  
...  
Keyword(s):  
Coordination Polymer ◽  
Two Dimensional ◽  
Valence Tautomerism ◽  
Thermally Induced

scholarly journals Investigating valence tautomerism presence in compounds of Co and naphthoquinone

2014 ◽  
Vol 70 (a1) ◽  
pp. C1257-C1257
Author(s):  
Marcos Ribeiro ◽  
Humberto Stumpf ◽  
Carlos Pinheiro
Keyword(s):  
Coordination Compounds ◽  
Metal Ion ◽  
Organic Ligand ◽  
Electronic States ◽  
Functional Materials ◽  
Structural Features ◽  
X Ray Diffraction ◽  
Valence Tautomerism ◽  
X Ray ◽  
Vis Spectroscopy

The search for new functional materials involves the development of bistable molecules exhibiting different electronic states with distinct properties at the ambient condition (temperature, pressure, illumination) of application. Coordination compounds, which present electron transfer between metal ion and an organic ligand associated with a change in electron multiplicity of the metal ion, are named valence tautomers(VT)[1]. The chemical equilibrium between two distinct electronic states in VT can be induced by temperature and pressure change as well as by soft X-ray and light irradiation. Thermodynamic and structural data highlighting the mechanisms of the valence tautomerism interconversion can be found in the literature for materials build up with cobalt and benzoquinones such as the 3,5-di-t-butyl-semiquinonate. However, to the best of our knowledge, there is no example of compounds showing VT build up with cobalt and naphthoquinones. In the present work 2-hydroxy-1,4-naphthoquinone (law) has been used as redox active ligands in the search for new VT compounds with cobalt. Three new coordination compounds of cobalt and 2-hydroxy-1,4-naphthoquinone (law), [Co(law)2(im)2], [Co(law)2(phen)] e [Co(law)2(bpy)] were synthesized and characterized by infrared (IR), UV-vis spectroscopy, electron paramagnetic resonance (EPR) and cyclic voltammetry. The three dimensional structures were determined using single crystal X-ray diffraction techniques. However, within the investigated temperature range neither X-ray diffraction nor EPR data showed the presence of VT in the materials, mainly due to the electrochemical properties of the 2-hydroxy-1,4-naphthoquinone. Nevertheless the structural features of the compounds as well as their supramolecular packing motifs suggest that naphthoquinones can be an alternative for the synthesis of compounds showing valence tautomerism[3].

Insights into the Chemistry and Structural Features of the Copper(II) 2,2′-Bipyridyl–Thiosulfate System

2020 ◽  
Vol 73 (1) ◽  
pp. 43
Author(s):  
Eric W. Ainscough ◽  
Sidney S. Woodhouse ◽  
Andrew M. Brodie ◽  
Graham H. Freeman ◽  
Paul G. Plieger
Keyword(s):  
Current Problem ◽  
Structural Features ◽  
Oxidation States ◽  
Gold Leaching ◽  
Thermally Induced ◽  
X Ray ◽  
X Ray Crystallography ◽  
Coinage Metals ◽  
The Rich ◽  
A Current

In this paper, we present our findings on a series of copper(ii) 2,2′-bipyridyl (bipy) complexes that inhibit the oxidation of thiosulfate, a current problem in the gold leaching process. The formation of six complexes, five of which have been structurally characterized by X-ray crystallography, illustrate a thermally induced, controllable switching between oxidation states, which in turn inhibits the oxidation of thiosulfate. These findings give further insight and understanding into the rich chemistry of the coinage metals and the hydrolytic processes involved with gold leaching.

Quantum chemical modeling of magnetically bistable metal coordination compounds. Synchronization of spin crossover, valence tautomerism and charge transfer induced spin transition mechanisms

2016 ◽  
Vol 45 (30) ◽  
pp. 12103-12113 ◽  
Author(s):  
V. I. Minkin ◽  
A. A. Starikova ◽  
A. G. Starikov
Keyword(s):  
Quantum Chemical ◽  
Coordination Compounds ◽  
Spin Crossover ◽  
Dynamic Behaviour ◽  
Spin Transition ◽  
Heterometallic Complexes ◽  
Chemical Modeling ◽  
Valence Tautomerism ◽  
Thermally Induced ◽  
Intramolecular Rearrangements

Heterometallic complexes of 1,10-phenanthroline-5,6-dione exhibiting unprecedented dynamic behaviour due to synchronized thermally induced intramolecular rearrangements were computationally studied.

Electron microscopy and diffraction studies of polyimides

1983 ◽  
Vol 41 ◽  
pp. 28-29
Author(s):  
O.C. de Hodgins ◽  
K. R. Lawless ◽  
R. Anderson
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Structural Features ◽  
Inert Atmosphere ◽  
Polyimide Films ◽  
Resolution Electron ◽  
The Matrix ◽  
High Resolution Electron Microscope ◽  
Diffraction Patterns ◽  
Polymeric Samples

Commercial polyimide films have shown to be homogeneous on a scale of 5 to 200 nm. The observation of Skybond (SKB) 705 and PI5878 was carried out by using a Philips 400, 120 KeV STEM. The objective was to elucidate the structural features of the polymeric samples. The specimens were spun and cured at stepped temperatures in an inert atmosphere and cooled slowly for eight hours. TEM micrographs showed heterogeneities (or nodular structures) generally on a scale of 100 nm for PI5878 and approximately 40 nm for SKB 705, present in large volume fractions of both specimens. See Figures 1 and 2. It is possible that the nodulus observed may be associated with surface effects and the structure of the polymers be regarded as random amorphous arrays. Diffraction patterns of the matrix and the nodular areas showed different amorphous ring patterns in both materials. The specimens were viewed in both bright and dark fields using a high resolution electron microscope which provided magnifications of 100,000X or more on the photographic plates if desired.

Skeletal elements of crinoid echinoderms: High-resolution structural and microanalytical results

1983 ◽  
Vol 41 ◽  
pp. 194-195
Author(s):  
D. F. Blake ◽  
L. F. Allard ◽  
D. R. Peacor
Keyword(s):  
High Resolution ◽  
Marine Invertebrates ◽  
Sea Urchins ◽  
Structural Features ◽  
Sea Stars ◽  
High Resolution Tem ◽  
Relationship Of ◽  
The Relationship ◽  
Insight Into

Echinodermata is a phylum of marine invertebrates which has been extant since Cambrian time (c.a. 500 m.y. before the present). Modern examples of echinoderms include sea urchins, sea stars, and sea lilies (crinoids). The endoskeletons of echinoderms are composed of plates or ossicles (Fig. 1) which are with few exceptions, porous, single crystals of high-magnesian calcite. Despite their single crystal nature, fracture surfaces do not exhibit the near-perfect {10.4} cleavage characteristic of inorganic calcite. This paradoxical mix of biogenic and inorganic features has prompted much recent work on echinoderm skeletal crystallography. Furthermore, fossil echinoderm hard parts comprise a volumetrically significant portion of some marine limestones sequences. The ultrastructural and microchemical characterization of modern skeletal material should lend insight into: 1). The nature of the biogenic processes involved, for example, the relationship of Mg heterogeneity to morphological and structural features in modern echinoderm material, and 2). The nature of the diagenetic changes undergone by their ancient, fossilized counterparts. In this study, high resolution TEM (HRTEM), high voltage TEM (HVTEM), and STEM microanalysis are used to characterize tha ultrastructural and microchemical composition of skeletal elements of the modern crinoid Neocrinus blakei.

Study of the Molecular Architecture of Keratin Filaments by Electron Microscopy

1982 ◽  
Vol 40 ◽  
pp. 118-119
Author(s):  
U. Aebi ◽  
P. Rew ◽  
T.-T. Sun
Keyword(s):  
Electron Microscopy ◽  
Structural Organization ◽  
Cell Types ◽  
Structural Features ◽  
Molecular Architecture ◽  
The Past ◽  
Keratin Filaments ◽  
Different Types ◽  
10 Nm Filaments ◽  
Different Cell Types

Various types of intermediate-sized (10-nm) filaments have been found and described in many different cell types during the past few years. Despite the differences in the chemical composition among the different types of filaments, they all yield common structural features: they are usually up to several microns long and have a diameter of 7 to 10 nm; there is evidence that they are made of several 2 to 3.5 nm wide protofilaments which are helically wound around each other; the secondary structure of the polypeptides constituting the filaments is rich in ∞-helix. However a detailed description of their structural organization is lacking to date.

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