What do you guys know about delta, phi and gamma bonds? do any of them actually exist? Are there different types of each variety? for instance, if an f-orbital bonds with another, you could get a different type of bond depending on the values of ml. I guess the orbital with ml=0 (fz^3) is unlikely to make a bond since it's quite small around the middle, but the ml=-3 and ml=-1 varieties seem like they could make them... the ml=-2 looks like it might make something similar to a delta bond...

 

I can simulate all of these on my new orbital viewer software but iwonder if i am simulating anything real or not...

 

here's an example of a phi bond between two 4f orbitals with ml=-3:

 

 

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[ReCl8]2- has a metal metal quadruple bond in which one is a delta bond. There is also a chromium acetate dimer, whose exact formula I can't remember with a quadruple bond. It was made in the 1840's I believe and so this is not exactly new.

Ive actually researched this a bit more in the last few days and it seems that the maximum bond order so far discovered is sextuple. Apparently there is evidence that there cannot be any higher bond orders, although i don't know what evidence is. In a sextuple bond, one is sigma, two are pi and three are delta.

 

Phi bonds seem like a perfectly reasonable idea to me but i guess if you get enough electrons inbetween the nuclei eventually the situation will become unstable

We may be able to get more bonds if we get bigger atoms.

If you imagine the metal metal bond in the z direction then s, pz, f5z3-3zr2 are of the correct symmetry for sigma bonds (0 nodes), px, py, dxz,dyz, f5xz2-xr2 and f5yz2-yr2 are of the correct symmetry for pi bonding (1 node) , dx2-y2, dxy, fxyz and fzx2-zy2 are of the correct symmetry for delta bonding (2 nodes) and fy3-3yx2 and fx3-3xy2 are of the correct symmetry for phi bonding (3 nodes).

There are then other considerations, eg occupancy of the d and f orbitals, the symmetry of the number of other ligands requiring at least some of those orbitals, the diffuse nature and low electron density of f orbitals in the outer regions of the atom where overlap is required for bonding, then pi effects of the ligands eg are they pi donors or pi acceptors

My feeling is the f orbitals are too far buried in the atom to be able to bond in a phi fashion even if bonding isn't occupancy or symmetry forbidden