# Surface Fluorination/Hydroxyl Group

1. May 23, 2013

### citw

I'm a condensed matter student with limited knowledge of chemistry or bond notation. In the attached paper, I'm trying to understand what is meant by
$$\equiv\text{Ti}-\text{OH}$$
and
$$\equiv\text{Ti}-\text{F}$$
All I've been able to gather is that these represent "surface groups", although I'm not sure what is meant by "groups" in this context. I'm pretty new to bond notation, but I'm reasonably sure that the three horizontal lines represent a triple bond, but I'm not sure how I should interpret this in the context of surface species.

Finally, I know what a ligand is in the context of crystal field theory/coordination complexes, but I don't know what is meant by a "simple ligand exchange" that allows us to go from the first equation to the second. What does this mean and how exactly does this occur?

Any explanation/interpretation would be appreciated. No explanation is oversimplified, because this is all Greek to me at this point.

Last edited by a moderator: May 24, 2013
2. May 23, 2013

### Staff: Mentor

To quote the paper:

My understanding is it doesn't mean triple bond per se, just the Ti atom on the surface, bonded to the rest of the material in an unspecified way.

3. May 23, 2013

### citw

But the notation has to mean something, right? I wouldn't think they'd choose that notation arbitrarily. I've attached another paper on Si that uses the same thing, with

$$\equiv\text{Si}-\text{O}^-$$

Last edited by a moderator: May 24, 2013
4. May 23, 2013

### Staff: Mentor

Which can only mean it is an established way of representing a surface atom. Note that in the second paper (Fig. 7) Si is not connected to other atoms in the crystal by the triple bond, it is connected mostly to oxygen atoms.

5. May 23, 2013

### citw

Yeah, that may well be true. One thing that they mention is silanol. Not that I have any familiarity with this, but here

you can see for "free silanol" that it appears (unless I'm wrong) to have three open bonds. I'm just not sure about this, because I can't find anything in literature about notation for surface groups using that "triple bond" notation. You may be correct.

6. May 24, 2013

### Staff: Mentor

Three bonds and triple bonds are different things. In siloxane bonds on the same image Si has three bonds going left as well, it is just a matter of where you "cut" them for the image.

I am going to delete attached papers for a copyright reasons.

7. May 24, 2013

### citw

Very true, but don't three (horizontal) lines imply a triple bond?

http://en.m.wikipedia.org/wiki/Triple_bond

Do you know what the notation used in the papers refers to?

Sorry, I wasn't sure about the protocol.

8. May 29, 2013

### chemisttree

The three bonds for the silanol example mean that there are three bonds to other silicon atoms in the case of silicon metal. If the articles discussed surface silanols on glass or fused silica, the three lines represent three Si-O-Si bonds to the bulk of the solid glass. Same for the titanium example.

9. May 29, 2013

### citw

Here is a link to both examples:

http://pubs.acs.org/doi/abs/10.1021/jp036735i (TiO2)

http://www.sciencedirect.com/science/article/pii/S0142961203006835 (Si-O-/Si-OH)

In the TiO2 example, the surface is OH or F terminated, with the Ti coordinated to five O ions. So it might be written as $$\text{Ti}_\text{5c}-\text{F}$$

An article in Nature that shows this specific case a bit more clearly can be found at

http://www.nature.com/nature/journal/v453/n7195/full/nature06964.html

What is the significance of the three lines in this case?

Last edited by a moderator: May 6, 2017
10. Jun 7, 2013

### chemisttree

I can't access the Nature article.

11. Jun 7, 2013

The indicate that the adsorbed species (F, OH) are situated above a Ti atom *surface site* on the TiO2 substrate. The three lines indicate the bulk, and do not imply a particular model of bonding.

12. Jun 8, 2013

### citw

Unfortunately, I don't think allowed to post it here.

13. Jun 8, 2013

### citw

Have you seen this before? I'm trying to understand if this is an established notation.