Oxocarbon Dianions Research Articles

Assemblies of Two New Metal−Organic Frameworks Constructed from Cd(II) with 2,2‘-Bipyrimidine and Cyclic Oxocarbon Dianions CnOn2- (n = 4, 5)

Two extended networks of Cd(II) with 2,2‘-bipyrimidine (bpym) and cyclic oxocarbon dianions CnOn2- (n = 4, 5) with formulas [Cd(C4O4)(bpym)0.5(H2O)] (1) and [Cd(C5O5)(bpym)0.5(H2O)] (2) have been synthesized and characterized by single-crystal X-ray diffraction studies. Structural determination reveals that, in compounds 1, each Cd center lies in a seven-coordinate environment bonded to two bpym nitrogen atoms and five oxygen donors from four squarate and one water molecules. The squarate acts as a bridging ligand with two different binding modes, a tetramonodentate (μ4) and a bis-bridging (μ4) coordination mode, linking the Cd(II) ions to form a two-dimensional (2D) metal−squarate layer. Adjacent layers are then mutually linked via bridges of bis-bidentate bpym ligands constructing a three-dimensional (3D) triangular metal−organic framework (MOF). In compound 2, each Cd center lies in an eight-coordinate environment bonded to two bpym nitrogen atoms and six oxygen donors from three croconate ligands and ...

Self-Assembly of Neutral Platinum-Based Supramolecular Ensembles Incorporating Oxocarbon Dianions and Oxalate

Five neutral platinum-based macrocycles incorporating cyclic oxocarbondianions, squarate and croconate and their acyclic analogue, oxalate, have been synthesized in 90-95% yield via self-assembly. The combination of the diplatinum molecular clip with all three dianions afforded molecular rectangles, whereas a platinum-based 60 degrees acceptor unit produced a supramolecular rhomboid with croconate ion but a triangle with squarate ion. In all cases, multinuclear NMR spectra were consistent with the formation of single highly symmetrical species. The three rectanglular and the rhomboid assemblies were characterized by single-crystal X-ray crystallography. The triangular species was characterized by FAB mass spectrometry.

Hydration of cyclic oxocarbon dianions, such as c-C 5O 52−, in the gas phase. Charge reduction of hydrates by electron detachment or proton transfer : Energy barriers for electron detachment and electron transfer

The cyclic oxocarbon dianions C n O n 2− are known to exist in aqueous solution, but have not been previously produced in the gas phase. Using electrospray, the n=5 (croconate) and n=6 (rodhizonate) dianions were easily observed in the gas phase. Croconate was used for all further studies. The dianion was observed only when solvated by two or more H 2O molecules. The hydration equilibria ( n−1, n) for the croconate dianion: C 5O 5(H 2O) n−1 2−+H 2O=C 5O 5(H 2O) n 2− were determined for n=3–9, with a reaction chamber attached to a triple quadrupole mass spectrometer, obtaining thus values for Δ G°, Δ H° and Δ S° of the above hydration reactions. At temperatures above 50 °C and low water partial pressures that led to hydrates below n=2, charge reduction by electron detachment was observed. Solvents with higher gas phase acidity, such as methanol, led to charge reduction by proton transfer from methanol to the dianion. The C 5O 5(H 2O) 2 2− was stable towards electron detachment even though the electron affinity of the monoanion EA(C 5O 5(H 2O) 2 −) evaluated at the B3LYP/6-311++G(d,p) level was negative. This result demonstrates that the electron detachment is impeded by the existence of a Coulomb barrier for the reverse, electron attachment, reaction. Electron transfer from the dianions to neutral molecules B that have positive electron affinities, such as nitrobenzene, is also impeded by a Coulomb barrier. This is indicated by the formation of complexes (C 5O 5(H 2O) n B m ) 2− at 50 °C and lower temperatures, in which the double charge has remained on the C 5O 5 group. The bonding in (C 5O 5(H 2O) n B m ) 2− is discussed. However, electron transfer to compound B with higher electron affinities such as di-nitrobenzene is observed at 50 °C.

Are oxocarbon dianions aromatic?

Assessment of the cyclic electron delocalization of the oxocarbon dianions, C(n)()O(n)()(2)(-) and their neutral counterparts C(n)()O(n)() (n = 3-6), by means of structural, energetic, and magnetic criteria, shows that C(3)O(3)(2)(-) is doubly aromatic (both sigma and pi cyclic electron delocalization), C(4)O(4)(2)(-) is moderately aromatic, but C(5)O(5)(2)(-), as well as C(6)O(6)(2)(-), are less so. Localized orbital contributions, computed by the individual gauge for localized orbitals method (IGLO), to the nucleus-independent chemical shifts (NICS) allow pi effects to be disected from the sigma single bonds and other influences. The C-C(pi) contribution to (NICS(0,pi) (i.e., at the center of the ring) in oxocarbon dianions decreases with ring size but shows little ring size effect at points 1.0 A above the ring. On the basis of the same criteria, C(4)O(4) exhibits cyclic electron delocalization due to partial occupancy of the sigma CC bonds. However, the dissociation energies of all the neutral oxocarbons, C(n)()O(n)(), are highly exothermic.

Molecular Vibrational Constants and Chemical Bonding in the Cyclic Oxocarbon Dianions Cn0n−2(n=3, 4 and 5)

Abstract By means of an ab initio force field and the mean amplitudes of vibration of the cyclic oxocarbon dianions CnOn with n= 3, 4 and 5, it has been found that the ground-state aromaticity order in the series is: deltate (n=3) > squarate (n=4) > croconate (n=5) ion. The reactivity of these molecules with respect to an electro-philic attack follows the order croconate > squarate > deltate ion.

Topological Charge Stabilization Rule and Quasi-Aromaticity

Abstract Stabilities of the oxocarbon dianions and some quasi-aromatic compounds can be rationalized in terms of Gimarc’s topological charge stabilization rule. The term “quasi-aromatic” is recommended for describing those non-aromatic compounds which behave like aromatics owing to the operation of this rule.

A quantum chemical study of the cyclic oxocarbon dianions C nO n−2 ( n = 3, 4, 5 and 6) : II. Electronically excited states

The electronic spectra of the title compounds have been studied by the ab-initio SCF-CI and CNDO/S methods. Excited energies for the singlet—singlet transitions have been calculated and compared with the available experimental values and with earlier calculated data. The energies for the singlet—triplet transitions for the deltate and squarate dianions are also reported.

ChemInform Abstract: Structure‐Resonance Theory for Oxocarbons

Abstract An empirical valence bond structure-resonance theory is applied to monocyclic oxocarbon dianions and neutral oxocarbons. Graph theoretical techniques are used to carry out the calculations. The resonance energies are partitioned among various types of resonance interactions. Carbonyl group covalent-ionic resonance is the most prevalent type of stabilizing resonance term in every case (⩾50%). Resonance energies, charge distributions, and bond orders are compared with the results of MO calculations, and with relevant experimental data. A qualitative valence bond interpretation of the concept of aromaticity is proposed based on cyclic terms that appear in the graph of the empirical structure-resonance theory Hamiltonian matrix. On this basis, all oxocarbon dianions are found to be resonance stabilized and aromatic, whereas the neutral oxocarbons are nonaromatic but still stabilized by resonance.

A MINDO/3 study on the monoelectronic reduction of carbon monoxide: The acetylenediolate dianion as the first member and as the common precursor of all the cyclic oxocarbon dianions

The formation of acetylenediolate (C 2O 2 2−) in the monoelectronic reduction of carbon monoxide has been studied by the MINDO/3 method. According to the present results, carbon monoxide is first reduced to its radical anion, which adds to a second molecule of carbon monoxide to form the ethylenedione radical anion, which is then further reduced to C 2O 2 2−. The partial oxidation of acetylenediolate to oxalate dianion, as well as the electrochemical synthesis of squarate dianion from carbon monoxide, are interpreted in terms of the proposed mechanism.

Structure-resonance theory for oxocarbons

An empirical valence bond structure-resonance theory is applied to monocyclic oxocarbon dianions and neutral oxocarbons. Graph theoretical techniques are used to carry out the calculations. The resonance energies are partitioned among various types of resonance interactions. Carbonyl group covalent-ionic resonance is the most prevalent type of stabilizing resonance term in every case (⩾50%). Resonance energies, charge distributions, and bond orders are compared with the results of MO calculations, and with relevant experimental data. A qualitative valence bond interpretation of the concept of aromaticity is proposed based on cyclic terms that appear in the graph of the empirical structure-resonance theory Hamiltonian matrix. On this basis, all oxocarbon dianions are found to be resonance stabilized and aromatic, whereas the neutral oxocarbons are nonaromatic but still stabilized by resonance.

ChemInform Abstract: A SIMPLE MODEL FOR THE ELECTRONIC STRUCTURE OF OXOCARBON DIANIONS

Chemischer InformationsdienstVolume 14, Issue 2 Physical Organic Chemistry ChemInform Abstract: A SIMPLE MODEL FOR THE ELECTRONIC STRUCTURE OF OXOCARBON DIANIONS A. MOYANO, A. MOYANOSearch for more papers by this authorF. SERRATOSA, F. SERRATOSASearch for more papers by this author A. MOYANO, A. MOYANOSearch for more papers by this authorF. SERRATOSA, F. SERRATOSASearch for more papers by this author First published: January 11, 1983 https://doi.org/10.1002/chin.198302053Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, Issue2January 11, 1983 RelatedInformation

A simple model for the electronic structure of oxocarbon dianions

The aromaticity of oxocarbon dianions the acidity of the conjugated acids is explained by the participation of resonant forms bearing the aromatic carbocyclic nucleus C n ( n−2)+ . This point of view is supported by both the Kekulé index values of the limiting resonance structures and a localization of the π-MO's by the Edmiston—Ruedenberg criterion.

A simple model for the electronic structure of oxocarbon dianions

The aromaticity of oxocarbon dianions and the acidity of the conjugated acids is explained by the participation of resonant forms bearing the aromatic carbocyclic nucleus C n (n−2)+. This point of view is supported by both the Kekulé index values of the limiting resonance structures and a localization of the π-MO's by the Edmistorr-Ruedenberg criterion.

Applications of magnetic circular dichroism spectroscopy: excited states of oxocarbon dianions

Applications of magnetic circular dichroism spectroscopy: excited states of oxocarbon dianions

Are the oxocarbon dianions really aromatic?

Are the oxocarbon dianions really aromatic?

Theoretical analysis of the structure of monocyclic oxocarbon dianions [C nO n] −2 ( n = 3, 4, 5, 6)

The geometry and electronic structure of monocyclic oxocarbon dianions [C n O n ] −2 are studied on the basis of MINDO/2 wave functions. The optimized CC and CO bond lengths are in very good agreement with available X-ray crystallographic data. The calculations allow an encouraging interpretation of the differences observed between the vibrational spectra of squarate and croconate dianions. The theoretical ultraviolet spectrum (CNDO-CI method) reproduces quantitatively the experimental position and intensity of the first absorption band.