Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: mattmckee on 06/03/2014 14:55:31
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Why is Nickel tetra cyanide complex a sqaure planar? Whilst studying complex ions my A level group wanted to know and I wasn't exactly sure. Many books seemed to just say it is or they dont need to know.
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This is a good question. One might assume that the cyano ligands would adopt a tetrahedral arrangement around the nickel (II) center because this is what would be predicted by VSEPR. However, the geometry of the complex determines the energy of the molecular orbitals (essentially d orbitals) on the Ni atom. For Ni(II) Pd(II) and Pt(II), square planar is the most stable configuration, but Ni(0), Pd(0), Pt(0) complexes are almost all tetrahedral. This is because the square planar arrangement can stabilize some orbitals at the expense of others, as compared to tetrahedral. The M(II) cases can stabilize the occupied orbitals at the expense of the empty one, whereas the M(0) cases have all the d orbitals filled, so there is no net stabilization from the change in geometry. In this case VSEPR is the dominant effect.