New Challenges

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This is an open space when you can suggest new challenges. We cannot guarantee that the challenges suggested in this section will be selected for the discussion in the CB2017 unusual bond slam unless you can find two additional people that back up your challenge (i.e., a total of three speakers). Please keep in mind that the three speakers should be participants of the CB2017 conference. In such a case, the new challenge will be removed (by the organizers!) from this section and listed among the other challenges on the main page.

Inverted Metal to Carbonyl Donation in Ti3(CO)3 Cluster[edit]


  1. Cina Foroutan-Neijad
  2. --Henry (talk) 10:05, 21 August 2017 (CEST)


Ti3(CO)3 is the only known metal carbonyl complex with inverted donation, i.e. no σ-carbon to metal bonding but instead π-back donation from metal to the carbonyl ligands. Despite of this unusual bonding pattern, the bonding in this system is not discussed much in literature.[1],[2],[3]

Henry (talk) 15:08, 9 August 2017 (CEST)[edit]

Crystal structure search of carbonyl compounds
The following scatterplot shows a search of the Cambridge structure database as defined by the following query[4]. Here, the distance is that between any metal and the C (any bond type) and the angle is the one subtended at the C (any bond type for the C-O bond). Angles of interest are those < 90° which might indicate sideways π-interaction with the metal. There are indeed amazingly few examples in this region (red circles)! In contrast, CO2 as a metal ligand shows a much more diverse and interesting range of coordination modes.[5]

Silvi (talk) 10:37, 16 August 2017 (CEST)[edit]

ELF and QTAIM population analyses have been carried out (B3LYP/5-311++G(d)). The ELF=0.8 localization domains are displayed below with the following color code: magenta=core, green= di- and trisynaptic (bonds) redbrick= monosynaptic (lone pairs)

ELF=0.65 localization domains

The ELF picture shows tilted bridging carbonyls. Usually carbonyls are not tilted and the expected structure of Ti3(CO)3 would be D3h. The D3h structure can be considered as the transition state of reaction linking a pseudo clock-wise windmill conformer to a pseudo counter clock-wise conformer (different conformers in 2-D, same conformer in 3-D) which corresponds to the Ti-C symmetric bending calculated at 333.7 cm-1. The ELF and QTAIM populations are given by the table below

basin C3h D3h
C(Ti) 19.56 19.62
V(Ti,Ti,Ti) 0.90 (x2) 0.34 (x2)
V(Ti,C,Ti) 4.26 4.48
V(C,O) 1.86 2.0
V(O) 5.50 5.26
Ti 20.76 20.88
C 6.07 6.02
O 9.15 9.09

For both structures, the bonding is accounted for by five trisynaptic basins 2 V(Ti,Ti,Ti) and 3 V(Ti,C,Ti). The windmill structure is stabilized by a charge-charge electrostatic interaction between the oxygen of the carbonyl (QTAIM net charge -1.15 e-, QTAIM net charge of Ti +1.24), a rare example of intramolecular ionic bond.


  1. The critical re-evaluation of the aromatic/antiaromatic nature of Ti3(CO)3: a missed opportunity? DOI:10.1002/anie.200500364
  2. Recent advances in aromaticity and antiaromaticity in transition-metal systems, DOI:10.1039/C1PC90004H
  3. A Side-on-Bonded Polycarbonyl Titanium Cluster with Potentially Antiaromatic Character, DOI:10.1002/anie.200500364
  4. H. S. Rzepa, 2017, DOI:10.14469/hpc/2875
  5. H. S. Rzepa, 2017, DOI:cbpq

Positronium Hydride PsH[edit]


Bernard Silvi (not attending in person)


The positronium hydride PsH is an unique example of molecule having a spherical symmetry. The standard chemical notation as well as ball and stick models are totally unsuitable. I think that all interpretative methods (QTAIM, ELF, NBO, Hirshfeld partition) are not adapted to this problem.[1],[2],[3]

The radial density distributions of the positron (full line) and of the electrons (dashed line) versus the nucleus particle distance 'r' are displayed below.

305 x 2B4 px


  1. A. Ore, Phys. Rev., B 83, 665 (1951). DOI:10.1103/PhysRev.83.665
  2. Alexei M. Frolov and Vedene H. Smith Phys. Rev. A 55, 2662 (1997). DOI:10.1103/PhysRevA.55.2662
  3. C. le Sech and B Silvi, Chem. Phys, 236, 77-95 (1998). DOI:10.1016/S0301-0104(98)00210-9

Bonds during chemical reactions[edit]

  1. --Andreas Savin (talk) 10:05, 21 August 2017 (CEST)


  • Do electron pairs move like the arrows in textbooks?
  • Is the adiabatic picture sufficient, or do we need a real time-dependence, like in TDELF [1]?
  • Do all our bonding descriptors provide the same image?


  1. T. Burnus, M.A.L. Marques and E.K.U. Gross, Phys. Rev A. 71, 010501 (R) (2005).