[Pero]

Hi, I am an undergraduate student of Environmental Engineering in Zagreb and I have a nice little question about a complex ion I don't quite understand.

The chemical formula of this complex ion is [Fe(CN)₄]^3-.

What I would like you to help me on is how are the sp³d² hybrid molecular orbitals formed in such a compound and why are they formed in such a way that is described in the book I'm using (there are three d - orbitals of iron and six hybrid sp³d² - orbitals with CN^- ions in them)?

I must note that I have a generic knowledge in this huge course I'm taking at college and I'm quite stuck at this point.

I am very sorry that I might have not searched out the entire forum before I posted this.

Thank you in advance!

[Alpha-Omega]

Fe has what is called dsp hybridization/bonding.  And yes all three orbitals participate in the bonding.


Fe:  1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶

For Fe we can write Fe:  1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s² 

Fe³⁺:  [Ar]3d⁶

Fe²⁺: [Ar]3d⁵

So for Fe we have 3s² 3p⁶ 3d⁶

Fe forms d²sp³ Hybrids

These particular d2sp3 hybrids are combinations of two 3d, the 3s, and three 3p functions.

The 3s :  3 is the energy level, S is the subshell, 1 orbital

The 3p:  3 is the energy, p is the subshell, 3 orbitals p_x, p_y, and p_z

The 3d:  3 is the energy, d is the subshell, 5 orbitals d_yz, d_xz, dxy, d_x2-y2, and d_z2.

In general:

S subshell has only 1 orbital.
The p subshell has 3 orbitals.
The d subshell has 5 orbitals.
The f subshell has 7 orbitals.

In Fe there are 6 electrons in the 3d shell.

Hence, the designation  d²sp³ Hybrids

For octahedral iron complexes:  There are six d²sp³ hybrid orbitals. They are arranged in an octahedral layout so that each has four other orbitals at 90° to it and one at 180°.

The following links should help you too:

http://faculty.colostate-pueblo.edu/linda.wilkes/111/3c.htm

http://winter.group.shef.ac.uk/orbitron/AO-hybrids/d2sp3/index.html

http://www.chem1.com/acad/webtext/chembond/cb09.html

http://www.chemguide.co.uk/inorganic/complexions/whatis.html

[Pero]

Thank you very much, you've been a great help, but I already know the part with how many electrons may fit in how many orbitals!

One more question :

At homonuclear bonding of let's say for example Bohr's (B₂) molecule why does pz and pz orbitals overlay after px and py overlaying? Isn't the general rule that sigma bonds get formed before pi bonds?

Thanks!

[Kryolith]

Are you talking about time? 

[Alpha-Omega]

Try these links:

http://cnx.org/content/m14777/latest/

http://www.chem1.com/acad/webtext/chembond/cb08.html

Are you asking about which bonds will form regarding overlap and symmetry..because that is what that description sounds like to me....?  Basically,  the orbitals involved in the bonding will be those which give the molecule (in terms of bonding orbitals) the lowest energy, greatest overlap and the highests degree of symmetry.