Dear Sebastian,

Au-C bond length should be in the range of 1.76-2.06 depending on the nature of the carbon attached to the gold.

For more information, please use the following link:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2748951/

Also see table 2 in the following link:

http://www.nature.com/ncomms/2013/130726/ncomms3223/fig_tab/ncomms3223_T2.html

Hoping this will be helpful,

Rafik

Thanks a lot Rafik,

It does help a lot.

Regards,

Sebastian

Hello,

After performing the structural optimization and finding out the C-Au bond length, Natural Bond Orbital  (NBO) analysis can be performed to confirm the covalent bond order (e.g., Wiberg bond index). In a study involving S-Au bonding, the S-Au bond length was found to be 2.31 - 2.34 Angstrom and the bond order was close to 1 (Ref: Tetrahedron Letters 51 (2010) 5680–5685).

Regards, Padma Malar  

Having in mind that the concept of "bond" is just a concept - when performing QM calcualtions the distance between Au and C atoms is a pretty good measure of the existence of a bond. NBO analysis, as suggested above, can also give you informations about the (non)existence of the bond.

There is no ultimate way to determine a bond (order), but there are many different analysis tools available. Besides NBO/Wiberg bond index (make sure you have a balanced basis set description for C and Au), there are Mayer bond orders, Nalewajski-Mrozek bond orders, QT-AIM delocalization index ... 

Dear Sebastian,

I would suggest to do at least one or better all of the following: QTAIM, NCI and/or Natural Bond Orbitals.  The references to them you may find e.g. in our recent paper (see below, accessible also at the ResearchGate), and find that we were quite happy with these methods to qualitatively interpret a variety of bonds involving Au.  Make good pictures, get qualitative insights, and remember as Trzaskowski said above ""bond" is just a concept" - do not try to get too accurate or demanding. The bond length is of course a hint too.

"Noncovalent interactions determine the conformation of aurophilic complexes with

2-mercapto-4-methyl-5-thiazoleacetic acid ligands" DOI: 10.1039/c5dt01627d

Best of luck,

Grzegorz

Thank you all for your replies and insights. It was really enlightening and I'm sure it will be helpful.

In addition to those methods mentioned in the other replies, you could try the DDEC6 bond orders, which have many nice properties. See the following paper for details: T. A. Manz, "Introducing DDEC6 atomic population analysis: part 3. Comprehensive method to compute bond orders," RSC Advances, 7 (2017) 45552-45581 (http://dx.doi.org/10.1039/C7RA07400J ). This algorithm for computing bond orders is more widely applicable than alternative methods. It is implemented in the free Chargemol program (http://ddec.sourceforge.net).