Molecular Nanostuctures 1. Introduction. Carbon hybridization and allotropes Alexey A. Popov, IFW Dresden

Carbon

6 C Carbon Mass fraction in the Earth‘s crust:0.087% Atomic mass: Isotops: 12 C (98.9 %) 13 C (1.1 %) 14 C (nicht stabil, < 10 −9 %) Electron configuration:1s 2 2s 2 p 2... Material Carbon Nano-Material

6 C Carbon Material Bonding Molecular Structure Compounds Crystal Structure Carbon Nano-Material

6 C Carbon Material Bonding Molecular Structure Compounds Crystal Structure Properties Applications Characterization methods Theory Methods of Synthesis Carbon Nano-Material

Carbon: atomic structure main quantum number

Ground state C: 1s 2 2s 2 p 2 Carbon: atomic structure main quantum number

Ground state Excited state C: 1s 2 2s 2 p 2 C: 1s 2 2s 1 p 3 Carbon: atomic structure

Carbon: hybridization C-sp 3 C-sp 2 C-sp Excited state

C-sp 180º Carbon: sp-hybridization

C-sp 2 Three sp 2 hybrid orbitals 120º Carbon: sp 2 -hybridization

C-sp 3 Four sp 3 hybrid orbitals 109.5º Carbon: sp 3 -hybridization

Excited state C-sp 3 C-sp 2 C-sp Carbon: hybridization

Bonding between atoms: H 2 molecule, σ-bonding Constructive overlap

antibonding σ*-Orbital bonding σ-Orbital Bonding between atoms: H 2 molecule, σ-bonding

antibonding σ*-orbital bonding σ-orbital Atomic orbitals Molecular orbital bonding π-orbital antibonding π-orbital Bonding between atoms: σ- and π-bonding Molecular orbital Atomic orbitals

Bonding between atoms: σ- and π-bonding

+ C-sp 3 compounds: ethane C 2 H 6, single bond Only σ-bondng, single bond

C-sp 2 compounds: ethylene C 2 H 4, double bond σ-bondingπ-bonding σ- and π-bonding, double bond

C-sp 2 compounds: ethylene C 2 H 4, double bond σ-bondingπ-bonding σ- and π-bonding, double bond

C-sp compounds: acetylene C 2 H 2, triple bond π-bonding σ-bonding σ- and 2 π-bonds Triple bond

Single- versus double- versus triple- CC bonds Bond lengthBond energy 1.53 Å 368 kJ/mol 1.34 Å 611 kJ/mol (+243) 1.20 Å 820 kJ/mol (+209) Rotation around C-C bond has low barrier (free rotation at room temperature) Rotation around C=C bond requires breaking of π-bonding, hence high barrier (no rotation at room temperature, rigid framework)

C-sp 3 Bonding: Diamond The lattice structure of cubic diamond and ist elemntal cell The lattice structure of hexagonal diamond (Lonsdaleit).

C-sp bonding R(−C≡C−) n R, n = 2–14 The existence of carbyne is myth based on bad science and perhaps even wishful thinking. H. Kroto The existence of carbyne is myth based on bad science and perhaps even wishful thinking. H. Kroto

C-sp 2 bonding: butadiene, conjugation Band gap

Free electron, time independent Schrödinger equation kinetic energy k wave vector standing plane wave

Particle in a box (electron in the infinite potential well) 0 L x V = 0 V = ∞

Particle in a box (electron in the infinite potential well) 0 L x V = 0 V = ∞

Particle in a box (electron in the infinite potential well) 0 L x V = 0 V = ∞

Free electron versus electron in infinite well infinite well free electron dispersion relation

C-sp 2 bonding: butadiene, conjugation Band gap

Conjugated C-sp 2 systems: π-electron as an electron in a box

C-sp 2 bonding: increasing the conjugation length Increase of the π-system → decrease of the distance between the levels, decrease of the gap

Kekulé C-sp 2 bonding: benzene, PAH (Polycyclic aromatic hydrocarbons) Naphthalin Anthracen Phenanthren Tetracen Chrysen Coronen (Hexabenzobenzol) 1.39 Å 564 kJ/mol Bond lengthBond energy 1.53 Å 368 kJ/mol 1.34 Å 611 kJ/mol

„Small molecule“ Organic Semiconductors: Acenes pentacene tetracene naphthalene anthracene hexacene 3.97 eV 3.84 eV 2.72 eV 2.31 eV 1.90 eV gap popular material for OFET

C-sp 2 bonding: graphite

3.35 Å 1.42 Å C-sp 2 bonding: graphite

CC Bindungen 1.53 Å368 kJ/mol 1.34 Å611 kJ/mol(+243) 1.20 Å820 kJ/mol(+209) 1.53 Å357 kJ/mol Diamond Graphite 1.42 Å~474 kJ/mol intra 3.35 Å~4.5 kJ/mol inter Bond lengthBond energy 1.39 Å 564 kJ/mol Benzene

Graphite versus Diamond

The Nobel Prize in Chemistry 1996 was awarded jointly to Robert F. Curl Jr., Sir Harold W. Kroto and Richard E. Smalley "for their discovery of fullerenes".

The Nobel Prize in Physics 2010 was awarded jointly to Andre Geim and Konstantin Novoselov "for groundbreaking experiments regarding the two-dimensional material graphene"

Fullerene ~ 19,000 Nanotube ~66,000 Graphene ~32,000 Statistics for carbon structures in the title of publications

laser evaporation of graphite Discovery of fullerenes Mass-spectrometry analysis of the clusters

Mass Spectrometry Time of flight Magnet (Lorenz Force)

laser evaporation of graphite Mass spectra C 60 C 70 Discovery of fullerenes Mass-spectrometry analysis of the clusters

laser evaporation of graphite Mass spectra C 60 C 70

Richard Buckminster Fuller 1895–1983 “Buckminsterfullerene”

Monometallofullerenes

Publication with “Fullerene” in the title Kroto et al, Nature 1985

Wolfgang Krätschmer Donald R. Huffman

Fullerene formation mechanism: molecular dynamics