I would like to enlighten you further about this wonder solid, in the last post I explained what cyanide is and how it has the right orbitals for bonding to metals. I have shown you the orbitals on cyanide and how I will show you how they bind to metals to do things.
Firstly one of the sp orbitals (green) on the cyanide forms a sigma bond to the metal.
The next picture has the red and blue orbitals on the cyanide and the metal which interact to form the pi bond between the metal and the cyanide. This is at the same time as the sigma bond forms, in this way while electron density is transferred onto the metal from the cyanide through the sigma bond the cyanide removes electron density from the metal into the antibonding pi orbital. This is why cyanide is known as a pi-acid ligand, it also makes the ligand field of the cyanide very strong.
The green sp orbital is left behind and it pokes out into space to allow the bridges to be formed to the next metal.