Planar Tetracoordinate Carbon Research Articles

Planar Tetracoordinate Carbon Atoms in M 4 C Square Sheets (M = Ni, Pd, and Pt) Sandwiched between the Large π‐Coordinating Ligands [C 8 H 8 ] 2– and [C 9 H 9 ] –

Using the strategy of transition metal coordination together with that of large π-coordinating ligand complexation for planar tetracoordinate carbon (ptC) atoms, we present in this work a systematical DFT investigation on the possibility of ptC centers in M 4 C square sheets sandwiched in [C n H n ]M 4 C[C n' H n' ] complexes (M = Ni, Pd, Pt; n, n' = 8, 9) with the planar π-coordinating ligands [C 8 H 8 ] 2― and [C 9 H 9 ] ― . Introduction of a ptC center into an M 4 square sheet to form four effective ptC-M bonds helped to stabilize the [C n H n ]M 4 C[C n' H n' ] complexes thermodynamically, and the π-coordinating [C 8 H 8 ] 2― and [C 9 H 9 ] ― ligands were found to match the M 4 C middle decks both geometrically and electronically. Planar tetracoordinate boron (ptB) and nitrogen (ptN) behave similarly to ptC in these sandwich structures. These model sandwich complexes invite experimental syntheses and characterizations in order to open up a new area in coordination chemistry for planar tetracoordinate carbon and other non-metal atoms.

ChemInform Abstract: Stereochemistry and Catalysis with Zirconium Complexes

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Stability Rules of Main-Group Element Compounds with Planar Tetracoordinate Carbons

We have investigated the structures, stabilities, aromaticities, and Wiberg bond indices of four types of compounds (8-like, trapezia, umbrella-like, and quadrangle) containing planar tetracoordinate carbon (ptC), and the stability rules for the compound with ptC were concluded on the basis of extensive calculations. Generally, the stability or viability of compound with ptC strongly depends on the number of three-membered ring and conjugated three-membered ring, as well as pi electrons. These rules can be successfully used to identify the stability of other compounds reported in previous studies. On the basis of these rules, eight stable compounds with planar tetracoordinate nitrogen (ptN) are successfully constructed.

ChemInform Abstract: Compounds Containing a Planar-Tetracoordinate Carbon Atom as Analogues of Planar Methane

Over the past years the number of examples of compounds containing a planar-tetracoordinate carbon atom has increased. However, the presence of a carbon atom with a 360° sum of angles does not imply that the species is a derivative of planar methane; there must be an appropriate electronic stabilization. In the case of complexes 21a and 21b the central carbon atom is indeed stabilized by σ-donors and π-acceptors, as required for planar methane.

Planar Tetracoordinate Carbon Strips in Edge Decorated Graphene Nanoribbon

We predicted highly stable Cu-decorated zigzag graphene nanoribbons (ZGNRs) containing planar tetracoordinate carbon (ptC) strip(s). The computed electronic band structures suggest that the Cu-decorated ZGNRs are semiconducting. The Hirshfeld spin analysis suggests significant spin distribution at the edge ptC atoms. The two ptC strips are antiferromagnetically coupled, even though the edge Cu atoms do not exhibit significant magnetism. The stability of the multicenter ptC strip stems from both the highly delocalized pi orbital of ZGNRs and nearly perfect match between Cu-Cu bonding geometries and carbon atoms at the ZGNR edges.

Computationally Designed Families of Flat, Tubular, and Cage Molecules Assembled with “Starbenzene” Building Blocks through Hydrogen‐Bridge Bonds

Using density functional calculations, we demonstrate that the planarity of the nonclassical planar tetracoordinate carbon (ptC) arrangement can be utilized to construct new families of flat, tubular, and cage molecules which are geometrically akin to graphenes, carbon nanotubes, and fullerenes but have fundamentally different chemical bonds. These molecules are assembled with a single type of hexagonal blocks called starbenzene (D(6h) C(6)Be(6)H(6)) through hydrogen-bridge bonds that have an average bonding energy of 25.4-33.1 kcal mol(-1). Starbenzene is an aromatic molecule with six pi electrons, but its carbon atoms prefer ptC arrangements rather than the planar trigonal sp(2) arrangements like those in benzene. Various stability assessments indicate their excellent stabilities for experimental realization. For example, one starbenzene unit in an infinite two-dimensional molecular sheet lies on average 154.1 kcal mol(-1) below three isolated linear C(2)Be(2)H(2) (global minimum) monomers. This value is close to the energy lowering of 157.4 kcal mol(-1) of benzene relative to three acetylene molecules. The ptC bonding in starbenzene can be extended to give new series of starlike monocyclic aromatic molecules (D(4h) C(4)Be(4)H(4)(2-), D(5h) C(5)Be(5)H(5)(-), D(6h) C(6)Be(6)H(6), D(7h) C(7)Be(7)H(7)(+), D(8h) C(8)Be(8)H(8)(2-), and D(9h) C(9)Be(9)H(9)(-)), known as starenes. The starene isomers with classical trigonal carbon sp(2) bonding are all less stable than the corresponding starlike starenes. Similarly, lithiated C(5)Be(5)H(5) can be assembled into a C(60)-like molecule. The chemical bonding involved in the title molecules includes aromaticity, ptC arrangements, hydrogen-bridge bonds, ionic bonds, and covalent bonds, which, along with their unique geometric features, may result in new applications.

Pentaatomic planar tetracoordinate carbon molecules [XCAl3]q [(X,q) = (B,−2), (C,−1), (N,0)] with C–X multiple bonding

Among the fascinating planar tetracoordinate carbon (ptC) species, pentaatomic molecules belong to the smallest class, well-known as "pptC". It has been generally accepted that the planarity of pptC structure is realized via the "delocalization" of the p(z) lone pair at the central carbon and the ligand-ligand bonding interaction. Although "localization" is as key driving force in organic chemistry as "delocalization", the "localization" concept has not been applied to the design of pptC molecules, to the best of our knowledge. In this paper, we apply the "localization" strategy to design computationally a series of new pptC. It is shown that the central carbon atom and one "electronegative" ligand atom X (compared to the Al ligand) effectively form a highly localized C-X multiple bond, converting the lone pair at the central carbon to a two-center two-electron π-bond. At the aug-cc-pVTZ-B3LYP, MP2 and CCSD(T) levels, the designed 18-valence-electron pptC species [XCAl(3)](q); [(X,q) = (B,-2), (C,-1), (N,0)] are found to each possess a stable ptC structure bearing a C-X double bond, indicated by the structural, molecular orbital, Wiberg bonding, potential energy surface and Born-Oppenheimer molecular dynamics (BOMD) analysis. Moreover, our OVGF calculations showed that the presently disclosed (yet previously unconsidered) pptC structure of [C(2)Al(3)](-) could well account for the observed photoelectron spectrum (previously only ascribed to a close-energy fan-like structure). Therefore, [C(2)Al(3)](-) could be the first pptC that bears the highly localized C-X double bond that has been experimentally generated. Notably, the pptC structure is the respective global minimum point for [BCAl(3)](2-) and [NCAl(3)], and the counterion(s) would further stabilize [BCAl(3)](2-) and [C(2)Al(3)](-). Thus, these newly designed pptC species with interesting bonding structure should be viable for future experimental characterization. The presently applied "localization" approach complements well the previous "delocalization" one, indicating that the general "localization vs. delocalization" concept in organic chemistry can be effectively transplanted to exotic pptC chemistry.

A bifunctional strategy towards experimentally (synthetically) attainable molecules with planar tetracoordinate carbons

Bifunctional strategy, including efficiently utilizing valence electrons and offering steric protection, has been proposed to advance C(2)Al(4) global minimum with double planar tetracoordinate carbons (ptC) to a new family of ptC molecules which could be promising for synthetic realization.

Theoretical study on a family of organic molecules with planar tetracoordinate carbon

Based on the most stable structure of C 3B 2H 4 and its substitution of H with -Cl, -CH 2OH, -CHOH, -C O and -COOH groups, a series of derivatives containing the planar tetracoordinate carbon (ptC) atoms as well as crown ether-like compounds from the assembling of C 3B 2H 4 units have been constructed. At the B3LYP/6-311++G** and MP2/6-31G** levels of theory, these ptC compounds were predicted to be stable and they generally have large HOMO–LUMO gaps. The IR characteristic bands arising from the symmetrical and asymmetrical stretching vibrations of C–ptC, the stretching vibrations of C–B and B–H as well as the breath vibration of the two three-membered rings of C 3B 2 appear at 1000, 1250, 1600, 2800, and 1700 cm −1, respectively. Calculations also show that these ptC molecules have strong aromaticities and the ptC atom obeys the octal rule. Furthermore, the derivatives C 3B 2H 2(COOH) 2 and tetra-C 3B 2H 2-16-crown-4 can serve as the chelate ligands and form stable complexes with uranyl.

Simplest Neutral Singlet C2E4(E = Al, Ga, In, and Tl) Global Minima with Double Planar Tetracoordinate Carbons: Equivalence of C2Moieties in C2E4to Carbon Centers in CAl42−and CAl5+

Ab initio and DFT calculations have been carried out to search for the simplest neutral singlet species with double planar tetracoordinate carbons (dptCs) [the "simplest" means the species containing the least number (six) and types (two) of atoms]. Under the restrictions to the possible models (M1-M4) with dptCs and to the singlet electronic states, the B3LYP/6-31+G* scanning on the candidates, C(2)E(4) (E = the second- and third-row main group elements), only led to two minima (D(2h) C(2)Al(4) and C(2h) C(2)Be(4)) with stable DFT wave functions. The extensions to the heavier elements after the fourth row in the IIA and IIIA groups revealed that the D(2h) C(2)E(4) (E = Ga, In, and Tl) are also minima with dptCs but C(2)Ca(4) (C(2h)) is a first-order saddle point. Extensive explorations at the DFT level on their potential energy surfaces (PESs) further confirmed that the D(2h) C(2)E(4) (E = Al, Ga, In, and Tl) are the global minima, but the C(2h) C(2)Be(4) is a local minimum. The optimizations at the MP2 level distorted the D(2h) C(2)E(4) (E = Ga, In, and Tl) slightly and the distortion energies are less than 0.02 kcal/mol. The C(2)E(4) (E = Al, Ga, In, and Tl) with dptCs are 18.0, 18.3, 13.4, and 12.2 kcal/mol energetically more favorable than their nearest isomers, respectively, at the CCSD(T)//MP2 level with aug-cc-pVTZ for C and Al and aug-cc-pVTZ-PP for Ga, In, and Tl basis set. The substantial energy differences suggest their promise to be experimentally realized. The strong peak on the C(2)Al(4)(-) component in the time-of-flight mass spectrum from laser vaporization of a mixed graphite/aluminum may relate to the D(2h) C(2)Al(4) global minimum. The analyses of the electronic structures of C(2)Al(4) (D(2h)), CAl(4)(2-) (D(4h)) and CAl(5)(+)(D(5h)) indicates that the C(2) moiety in C(2)Al(4) is the equivalence of carbon centers in CAl(4)(2-) and CAl(5)(+) and unveils the reasons for their stability. The electronic structures of C(2)Al(4) and ethene are compared. On the one hand, an Al atom functions like an H atom because the eight more valence electrons of C(2)Al(4) than C(2)H(4) occupy four nonbonding orbitals and are not effectively utilized for bonding. On the other hand, an Al atom is different from an H atom because an Al atom has p electrons available for peripheral bonding around the C(2) moieties in C(2)Al(4), which further rationalize the origins for C(2)E(4) to achieve double ptCs.

B2C Graphene, Nanotubes, and Nanoribbons

We report a first-principles prediction of a new two-dimensional inorganic material, namely, the B(2)C graphene in which the boron and carbon atoms are packed into a mosaic of hexagons and rhombuses. In the B(2)C graphene, each carbon atom is bonded with four boron atoms, forming a planar-tetracoordinate carbon (ptC) moiety, a notion first conceived by Hoffmann et al. The B(2)C graphene is possibly a metal with a small overlap in the energy of conduction and valence bands. Like the carbon graphene and nanotubes, a B(2)C graphene sheet can be rolled into various forms of B(2)C nanotubes as well. Depending on the roll-up vector, the B(2)C nanotubes may become either a metal or a semiconductor. All B(2)C graphene nanoribbons are predicted to be uniformly metallic, regardless of their width and edge structure.

Perfect planar tetracoordinate carbon in neutral unsaturated hydrocarbon cages: A new strategy utilizing three‐dimensional electron delocalization

A new series of unsaturated pure and boron-substituted hydrocarbons containing a perfect planar tetracoordinate carbon (ptC) have been proposed by performing density functional computations. The ptC is effectively stabilized through three-dimensional delocalization of ptC's lone pair into pi-conjugated systems, by utilizing a new strategy opening a brand new way of designing ptC structures. Compared to previously proposed ptC-containing hydrocarbon cage compound, a neutral hydrocarbon designed here might be a more viable target for synthetic attempts.

Unusual Boron-Carbon Compounds Containing Planar Tetracoordinate and Pentacoordinate Carbons

Unusual boron-carbon compounds containing planar tetracoordinate carbon (ptC) and planar pentacoordinate carbon (ppC) were investigated using density functional theory (DFT) at B3LYP/6-311+G** level. These novel compounds are generally assembled with three types of stable structural units C3B2H4 with ptC, CB4H2 with ptC, and CB5H2 with ppC as well as linking elements—CHCH—. On the basis of calculation results the bonding features, spectroscopic properties, and the aromaticities of these novel boron-carbon compounds were discussed. Results show that as for the lowest-energy compounds contained ptC and ppC without being limited by symmetrical planes, stereo cis-structures of C2v symmetry are more stable than the corresponding planar trans-structures. Calculated nucleus-independent chemical shift (NICS) values show that the aromaticity of the center of the three-membered rings is the strongest. The total Wiberg bond indices (WBIs) of the ptC and ppC atoms of the most stable structures of the boron-carbon compounds indicate that the ptC and ppC obey the octal rule.

CSi2Ga2: a neutral planar tetracoordinate carbon (ptC) building block

Ever being a large curiosity, the "anti-van't Hoff/Le Bel" realm that is associated with tetracoordinate or hypercoordinate planar centers has made rapid progress. In particular, it has been disclosed that silicon and gallium can be embedded in various planar species. However, to our best knowledge, assembly of silicon- and gallium-embedded planar units has never been reported, though such assembled species might be used as potential nanoscale devices. Here we report the first attempt on how to design assembled molecular compounds featuring silicon- and gallium embedded planar tetracoordinate carbon (ptC) units. Taking the special silicon- and gallium-embedded ptC unit CSi2Ga2as an example, we performed density functional calculations on a series of model compounds [DM(CSi2Ga2)](q+) as well as the saturated compounds (Cl-)q[CpM(CSi2Ga2)](q+) (D = CSi2Ga2, Cp-(C5H5-); M = Li, Na, K, Be, Mg, Ca)and the more extended sandwich-like species. For the six metals, CSi2Ga2 can only be assembled in the "heterodecked sandwich" scheme (e.g., [CpM(CSi2Ga2)](q+)) so as to avoid cluster fusion. Interestingly, among all the designed sandwich species, CSi2Ga2 generally prefers to interact with the partner deck at the corner (Ga atoms) or face (CSi2Ga2 planes) sites. Such interaction types serve as an interesting growth pattern that might be applicable to the assembly of Si- and Ga-embedded ptC unit CSi2Ga2 into highly extended sandwich-like complexes. Our results for the first time showed that the Si- and Ga-embedded ptC unit CSi2Ga can act as a new type of building block. The present results are expected to enrich planar tetracoordinate carbon chemistry and metallocenes.

Planar Tetracoordinate Carbons in Cyclic Semisaturated Hydrocarbons

A series of planar tetracoordinate carbon molecules in cyclic semisaturated hydrocarbons resulting from the combination of the C5(2-) skeleton with saturated hydrocarbon fragments is reported. The electronic stabilization and the bonding situation are studied through the analyses of molecular orbitals and the electron localization function. The magnetic properties are also revised, giving particular attention to the induced magnetic field. These systems are the first semisaturated cycles containing a planar tetracoordinate carbon stabilized only by electronic factors.

Extended organoboron structures containing several planar tetracoordinate carbon atoms

101 Due to extensive studies of molecular electronic devices, the search for new one-dimensional organic and organometallic compounds with semiconducting, conducting, or superconducting properties is becoming ever more important [1]. The focus of this search is currently on different conjugated organic, organometallic, and inorganic polymeric systems [1–3]. Recently, nonclassical systems 1 – 3 with planar tetracoordinate carbon centers have been suggested for use as novel building blocks for polymers [4–6]:

Understanding the Planar Tetracoordinate Carbon Atom: Spiropentadiene Dication

The atoms in molecule theory shows that the spiropentadiene dication has a planar tetracoordinate carbon (ptC) atom stabilized mainly through the sigma bonds and this atom has a negative charge. The bonds to the ptC atom have less covalent character than the central carbon from neutral spiropentadiene. The total positive charge is spread along the structure skeleton. The analysis of the potential energy surface shows that the dication spiropentadiene has a 2.3 kcal/mol activation barrier for ring opening.

Novel Beltlike and Tubular Structures of Boron and Carbon Clusters Containing the Planar Tetracoordinate Carbon: A Theoretical Study of (C3B2)nH4 (n = 2−6) and (C3B2)n (n = 4−8)

By use of the most stable structure of C3B2H4 as a basic block, we construct two types of novel compounds containing the planar tetracoordinate carbon (ptC), beltlike compounds (C3B2)nH4 (n = 2−6) and tubular compounds (C3B2)n (n = 4−8). Equilibrium geometries, vibrational frequencies, and electronic spectra of both series of compounds have been determined by the density functional theory. The results reveal that the same direction arrangement of C2CB2 units with ptC will result in the most stable isomers of (C3B2)nH4 (n = 2−6). Predicted nucleus-independent chemical shift values show that the three-membered rings have aromaticity, whereas the six-membered rings have antiaromaticity. Calculations show that these compounds containing ptC atoms exhibit remarkable size dependence of their highest-occupied molecular orbital−lowest-unoccupied molecular orbital energy gaps and the first excitation energies.

The Si-doped planar tetracoordinate carbon (ptC) unit CAl3Si− could be used as a building block or inorganic ligand during cluster-assembly

Currently, the molecular assembly and growth from a small building block to the bulk compounds have become a focus in various fields. Ever being chemical curiosities, the “anti-van’t Hoff/Le Bel” realm that is associated with tetracoordinate or hypercoordiate planar centers has made vast progress. Being important in the fundamental research areas, the ptC species have potential applications in materials science. The existence of ptC in a divanadium complex and a large number of organometallic compounds have since been reported to possess ptC and these provide us with great hope that many more compounds with ptC building blocks may be synthesized in future. Herein, we report the assembly and stabilization of CAl3Si− in both the “homo-decked sandwich” and “hetero-decked sandwich” schemes at the B3LYP/6-311+G(d) level. We show that while the Si-doped indeed introduces much complexity during assembly, the electronic and structural integrity feature of CAl3Si− is well conserved during cluster-assembly, characteristic of a “superatom”. This study should be helpful in understanding the hetero-doped assembly mechanism of the ptC chemistry. Moreover, the present results are expected to enrich the flat carbon chemistry, superatom chemistry, metallocenes and combinational chemistry.

Hydrometal Complexes with More than One Planar and Quasi-Planar Tetracoordinate Carbon Atom: From Hydrogen-Surrounded Pieces to the Rudiment of Hydrogen-Sealed Nanotubes

The feasibilities of one- and two-dimensional extensions of previously reported CM4H4 (M = Ni and Cu) units, which may result in species with more than one independent planar or quasi-planar tetracoordinated carbon (ptC or qptC) atom, have been studied with ab initio density functional theory calculations, and the results reveal that such extensions are possible. Significantly, some of the located hydrogen-surrounded piecelike genuine minima in general form CnM2n+2H2n+2 (n = 3, 4; M = Ni, Pd, Pt) may be the first examples of hydrometal complexes with three or four ptC and qptC atoms, while hydrogen-sealed minima in general forms C5nM5n+5H10 and C6nM6n+6H12 (n = 2, M = Ni, Pd) also may be novel examples of nanotubes with a large number of qptC atoms. These species with more than one ptC or qptC show both aesthetic appeal and predictable characteristics from a practical perspective. No new elements or groups are introduced into the system during the extensions. The results can provide some helpful ideas to synthetic chemists in their exploration activities to obtain such interesting neutral substance in macroquantity.