Question

1. Is Bis(salicylaldehydato)nickel(II) dihydrate octahedral or tetrahedral? Suggest geometry for Bis(salicylaldehydato)nickel(II) dihydrate and support your assignments using magnetic measurement data (Ueff = 3.68) and electronic configuration drawings.  (Use correct geometries in 3D space). Why are the structures the way they are? (High spin vs low spin ligands, magnetic moment and number of unpaired electrons could explain this)

Answer 1

Bis(salicylaldehydato)nickel(II) dihydrate octahedral or tetrahedral :

Name of this molecule suggests it to be octahedral , as there are six ligands; but when interpret magnetic data we get different picture. water molecules might be part of outer sphere or this complex might equilibrate between octahedral or tetrahedral geometries.

Based on Data :

Ni (II) : d⁸ ( issue of High spin vs low spin ligands does not arise as in both situations electrons will be filled in same manner).

magnetic measurement data, Ueff = 3.68

from spin only formula for both O_h ans T_d complexes : n = 2

     μ_so= √n(n+2) B.M. = 2.83 BM

But measured value is more than it, thus this indicates towards orbital contribution in magnetic moment.

( For an octahedral complex, orbital contributions are possible only when the t2g orbitals are differentially occupied and for a tetrahedral complex the t2 orbitals have to be differentially occupied. )

For O_h : t_2g6 e_g2 Orbital contribution is zero and magnetic moment is close to the spin only value .

For T_d : _e4 t₂4, Magnetic moment is higher than the spin only value as there is positive orbital contribution . μ_S+L = √{4S(S+1) + L(L+1)} B.M.

thus, based on magnetic moment data we can deduce that Bis(salicylaldehydato)nickel(II) dihydrate is tetrahedral .