Role of Topology in Spin Alignment of Organic Materials

1989 ◽  
Vol 173 ◽  
Author(s):  
Koichi Itoh ◽  
Takeji Takui ◽  
Yoshio Teki ◽  
Takamasa Kinoshita
Keyword(s):  
Single Crystal ◽  
High Spin ◽  
Organic Molecules ◽  
Valence Bond ◽  
Spin Alignment ◽  
Remarkable Feature ◽  
Density Distributions ◽  
Generalized Hubbard Model ◽  
State Spin

ABSTRACTIt is shown that the spin alignment in organic molecules as determined by single crystal ESR is highly dependent on the topological nature of their molecular pi electron networks. The three topological isomers of a high-spin molecule, biphenyl-n,n′-bis(phenylmethylene), abbreviated as BP-3,3′-BPM, BP-3,4′-BPM and BP-4,4′-BPM are taken as model compounds. BP-3,3′-BPM has a unique spin alignment for which the simple molecular orbital and valence bond methods predict different ground-state spin multiplicities. The above remarkable feature of spin alignment in organic high-spin molecule is interpreted in terms of their spin density distributions which have been determined by a single crystal ENDOR technique and compared with theoretical values calculated on the basis of a generalized Hubbard model as well as the Heisenberg model. This approach is extended to magnetic polymers in order to characterize their structure of the spin sites.

Role of High-Spin Molecules as Models for Organic Ferro- and Ferri-Magnets, and Pi-Toporegulated Magnetic Polymers

1989 ◽  
Vol 173 ◽  
Author(s):  
Takeji Takui ◽  
Makoto Endoh ◽  
Masayuki Okamoto ◽  
Kazunobu Satoh ◽  
Toyohiro Shichiri ◽  
...  
Keyword(s):  
Chemical Modification ◽  
Single Crystal ◽  
High Spin ◽  
Spin Structure ◽  
Esr Spectroscopy ◽  
Model Compounds ◽  
Spin Alignment ◽  
Methylene Bridge ◽  
Spin Structures

ABSTRACTA chemical modification exploiting functional groups such as ether and methylene as bridges between high-spin assemblies has been carried out as a usable method to increase dimensionality of spin structure. Exchange interaction via an ether or a methylene bridge between two high-spin assemblies has been studied by single-crystal ESR spectroscopy. Whether it is ferromagnetic or antiferromagnetic depends upon the substituted position of the bridge, demonstrating the important role of the topological nature in spin alignment. It turns out that superexchange interaction or hyperconjugation mechanism can dominate spin alignment between high-spin assemblies. Using the criteria obtained, model compounds for units of organic ferrimagnets have been synthesized. They possess antiferromagnetically-exchange coupled heterospins and the salient features of their spin structures are characterized in terms of the spin density distribution as determined by single-crystal 1H-ENDOR (Electron-Nuclear-DOuble Resonance) spectroscopy.

Resolving the Quadruple Bonding Conundrum in C2 Using Insights Derived from Excited State Potential Energy Surfaces: A Molecular Orbital Perspective

2019 ◽  
Author(s):  
Ishita Bhattacharjee ◽  
Debashree Ghosh ◽  
Ankan Paul
Keyword(s):  
Excited State ◽  
Potential Energy ◽  
Molecular Orbital ◽  
High Spin ◽  
Potential Energy Surfaces ◽  
Valence Bond ◽  
Deep Minimum ◽  
State Potential ◽  
Energy Surfaces ◽  
Mo Theory

The question of quadruple bonding in C<sub>2</sub> has emerged as a hot button issue, with opinions sharply divided between the practitioners of Valence Bond (VB) and Molecular Orbital (MO) theory. Here, we have systematically studied the Potential Energy Curves (PECs) of low lying high spin sigma states of C<sub>2</sub>, N<sub>2</sub> and Be<sub>2</sub> and HC≡CH using several MO based techniques such as CASSCF, RASSCF and MRCI. The analyses of the PECs for the<sup> 2S+1</sup>Σ<sub>g/u</sub> (with 2S+1=1,3,5,7,9) states of C<sub>2</sub> and comparisons with those of relevant dimers and the respective wavefunctions were conducted. We contend that unlike in the case of N<sub>2</sub> and HC≡CH, the presence of a deep minimum in the <sup>7</sup>Σ state of C<sub>2</sub> and CN<sup>+</sup> suggest a latent quadruple bonding nature in these two dimers. Hence, we have struck a reconciliatory note between the MO and VB approaches. The evidence provided by us can be experimentally verified, thus providing the window so that the narrative can move beyond theoretical conjectures.

Structural, magnetic and Mössbauer spectroscopic studies of the [Fe(3-bpp)2](CF3COO)2 complex: role of crystal packing leading to an incomplete Fe(ii) high spin ⇋ low spin transition

CrystEngComm ◽  
2021 ◽  
Vol 23 (15) ◽  
pp. 2854-2861
Author(s):  
Kristian Handoyo Sugiyarto ◽  
Djulia Onggo ◽  
Hiroki Akutsu ◽  
Varimalla Raghavendra Reddy ◽  
Hari Sutrisno ◽  
...  
Keyword(s):  
High Spin ◽  
Crystal Packing ◽  
Spin Transition ◽  
Spectroscopic Studies ◽  
Mononuclear Complex

Mononuclear complex [Fe(3-bpp)2](CF3COO)2 exhibits a thermal (HS + HS) ⇋ (HS + LS) transition at ∼226 K which is not associated with any crystallographic transition.

scholarly journals Did Cyclic Metaphosphates Have a Role in the Origin of Life?

2021 ◽  
Author(s):  
Thomas Glonek
Keyword(s):  
Organic Molecules ◽  
Water Soluble ◽  
Holliday Junction ◽  
Additional Energy ◽  
Condensed Phosphate ◽  
Geological Processes ◽  
The Origin Of Life ◽  
Complex Forms ◽  
Self Replication

AbstractHow life began still eludes science life, the initial progenote in the context presented herein, being a chemical aggregate of primordial inorganic and organic molecules capable of self-replication and evolution into ever increasingly complex forms and functions.Presented is a hypothesis that a mineral scaffold generated by geological processes and containing polymerized phosphate units was present in primordial seas that provided the initiating factor responsible for the sequestration and organization of primordial life’s constituents. Unlike previous hypotheses proposing phosphates as the essential initiating factor, the key phosphate described here is not a polynucleotide or just any condensed phosphate but a large (in the range of at least 1 kilo-phosphate subunits), water soluble, cyclic metaphosphate, which is a closed loop chain of polymerized inorganic phosphate residues containing only phosphate middle groups. The chain forms an intrinsic 4-phosphate helix analogous to its structure in Na Kurrol’s salt, and as with DNA, very large metaphosphates may fold into hairpin structures. Using a Holliday-junction-like scrambling mechanism, also analogous to DNA, rings may be manipulated (increased, decreased, exchanged) easily with little to no need for additional energy, the reaction being essentially an isomerization.A literature review is presented describing findings that support the above hypothesis. Reviewed is condensed phosphate inorganic chemistry including its geological origins, biological occurrence, enzymes and their genetics through eukaryotes, polyphosphate functions, circular polynucleotides and the role of the Holliday junction, previous biogenesis hypotheses, and an Eoarchean Era timeline.

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