Carbon Flatland:  Planar Tetracoordinate Carbon and Fenestranes

Keese, Reinhart

doi:10.1021/cr050545h

Cited by 349 publications

(229 citation statements)

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“…A simple 908 twist results in a 0.5 eV per C energy stabilization favoring the linear polymer with tetrahedral carbon, 23. This is hardly surprising given what we know of carbon chemistry, and the absence of special factors stabilizing squareplanar carbon (a geometry close to the heart of one of us [13,14] ). Carbon is the only one of the Group 14 elements known to have metastable, kinetically persistent 1D (carbyne, nanotubes) and 2D (graphene) allotropes (and 0D, as well, counting the fullerenes).…”

Section: Carbon: Clearly Carbon (Open Circles Inmentioning

confidence: 99%

“…Beyond these, the choices are somewhat arbitrary. The 2D starting geometries shown in Figure 2 include the honeycomb net or graphene (10), two-layer graph-A C H T U N G T R E N N U N G enes (11 and 12), the square-planar sheet (13), kagome net (14), wavy or corrugated square sheet (15), "cubic" planar or double square sheet (16), rhombohedral planar or trigonal prism sheet (17), and a triangular sheet (18).…”

Section: Introductionmentioning

confidence: 99%

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Exploring Group 14 Structures: 1D to 2D to 3D

Wen

Cahill

Hoffmann

2010

Chemistry A European J

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Various one-, two- and three-dimensional Group 14 (C, Si, Ge, Sn, and Pb) element structures at P = 1 atm are studied in this work. As expected, coordination number (CN)--not an unambiguous concept for extended structures--plays an important part in the stability of structures. Carbon not only favors four-coordination, but also is quite happy with pi-bonding, allowing three- and even two-coordination to compete. Highly coordinated (CN > 4) discrete carbon molecules are rare; that "saturation of valence" is reflected in the instability of C extended structures with CN > 4. Si and Ge are quite similar to each other in their preferences. They are less biased in their coordination than C, allowing (as their molecular structures do) CN = 5 and 6, but tending towards four-coordination. Sn and Pb 3D structures are very flexible in their bonding, so that in these elements four- to twelve-coordinate structures are close in energy. This lack of discrimination among ordered structures also points to an approach to the liquid state, consistent with the low melting point of Sn and Pb. The Group 14 liquid structures we simulate in molecular dynamics calculations show the expected, effective, first coordination number increase from 5.1 for Si to 10.4 for Pb. A special point of interest emerging from our study is the instability of potential multilayer graphene structures down Group 14. Only for C will these be stable; for all the other Group 14 elements pristine, unprotected, bi- and multilayer graphenes should collapse, forming "vertical" bonds as short as the in-plane ones.

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Section: Carbon: Clearly Carbon (Open Circles Inmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Exploring Group 14 Structures: 1D to 2D to 3D

Wen

Cahill

Hoffmann

2010

Chemistry A European J

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“…[5,6] In spite of the high yield reached for the synthesis of dienynes 2, the toxicity of the stannane compounds used in this approach remains a major problem. Another issue brought up by this type of cascade is the difficulty to completely eliminate the stannane residues from the isolated product.…”

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confidence: 99%

New Palladium‐Catalyzed Cascades: 4‐exo‐dig Cyclocarbopalladation Reaction Followed by Suzuki–Miyaura or Sonogashira Cross‐Coupling

et al. 2011

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“…Le Bel in 1874. However, after the proposal by Hoffmann and co-workers of tetracoordinate planar carbon in 1970, [1] extensive experimental and theoretical efforts were made to search for so-called anti-vant Hoff/ anti-Le Bel molecules (for recent reviews, see references [2][3][4]). In particular, the first experimental and theoretical realization of pentaatomic planar-coordinated carbon species in 1999 and 2000, [5][6][7][8] which confirmed earlier theoretical predictions, [9,10] has stimulated renewed interest in designing new tetracoordinate [11,12] and even hypercoordinate planar carbon molecules.…”

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confidence: 99%

CB₇⁻: Experimental and Theoretical Evidence against Hypercoordinate Planar Carbon

et al. 2007

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In organic chemistry, saturated carbon is known to bond to four ligands tetrahedrally, as first recognized independently by J. H. vant Hoff and J. A. Le Bel in 1874. However, after the proposal by Hoffmann and co-workers of tetracoordinate planar carbon in 1970, [1] extensive experimental and theoretical efforts were made to search for so-called anti-vant Hoff/ anti-Le Bel molecules (for recent reviews, see references [2][3][4]). In particular, the first experimental and theoretical realization of pentaatomic planar-coordinated carbon species in 1999 and 2000, [5][6][7][8] which confirmed earlier theoretical predictions, [9,10] has stimulated renewed interest in designing new tetracoordinate [11,12] and even hypercoordinate planar carbon molecules. [13][14][15][16] Notably, a series of hypercoordinate planar carbon species with boron ligands have been proposed. [13-15, 16a,c,e] Although none of these species is the global minimum on the potentialenergy surfaces, it has been suggested that they may be viable experimentally. The two proposed hexa-and heptacoordinate carbon species are D 6h CB 6 2À [13a,b,d, 14c, 15] and D 7h CB 7 À , [13b, 14c] respectively. The CB 7 À species is isoelectronic to B 8 2À , which we have shown previously to have a global-minimum D 7h structure with a heptacoordinate boron atom. [17][18][19][20] The D 7h CB 7 À can be viewed as replacing the central B À ion in B 82À by a C atom. Herein we report serendipitous experimental observation of CB 7 À . It was investigated by photoelectron spectroscopy (PES) and ab initio calculations, which showed that the observed species is a C 2v CB 7 À ion in which the C atom replaces a B À ion at the rim of the D 7h B 8 2À molecular wheel.The experiment was performed with a laser-vaporization cluster source and a magnetic-bottle photoelectron spectrometer (see Experimental Section).[21] We recently modified our cluster source by adding a 10-cm-long and 0.3-cm-diameter stainless steel tube to enhance cluster cooling.[22] We were using boron clusters, which we have previously investigated extensively, [17][18][19][20][23][24][25][26][27][28] to test the new cluster-source conditions. A 10 B-enriched disk target containing a small amount of Au was used as the laser-vaporization target.[23] Under certain conditions, when the vaporization laser was not perfectly aligned, we noted that in addition to the pure boron clusters we were also able to produce clusters containing one or two carbon atoms, as shown in Figure 1. The carbon most likely originated from impingement of the slightly misaligned vaporization laser beam on the stainless steel tubing. The trace amount of carbon contamination was ideal to produce boron clusters doped with only one or two carbon atoms, and the beam condition was stable and reproducible.The peak of the CB 7 À cluster is particularly intense with abundance as strong as those of the nearby pure B x À clusters (Figure 1). Its photoelectron spectra at two detachment laser wavelengths are shown in Figure 2. The 193-nm spectrum rev...

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Carbon Flatland: Planar Tetracoordinate Carbon and Fenestranes

Cited by 349 publications

References 184 publications

Exploring Group 14 Structures: 1D to 2D to 3D

Exploring Group 14 Structures: 1D to 2D to 3D

New Palladium‐Catalyzed Cascades: 4‐exo‐dig Cyclocarbopalladation Reaction Followed by Suzuki–Miyaura or Sonogashira Cross‐Coupling

CB₇⁻: Experimental and Theoretical Evidence against Hypercoordinate Planar Carbon

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Carbon Flatland: Planar Tetracoordinate Carbon and Fenestranes

Cited by 349 publications

References 184 publications

Exploring Group 14 Structures: 1D to 2D to 3D

Exploring Group 14 Structures: 1D to 2D to 3D

New Palladium‐Catalyzed Cascades: 4‐exo‐dig Cyclocarbopalladation Reaction Followed by Suzuki–Miyaura or Sonogashira Cross‐Coupling

CB7−: Experimental and Theoretical Evidence against Hypercoordinate Planar Carbon

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CB₇⁻: Experimental and Theoretical Evidence against Hypercoordinate Planar Carbon