​why don't we use Afbau principle in this case while filling the orbitals?

​why don't we use Afbau principle in this case while filling the orbitals? • Tetrahedral Complexes • The hybridisation involved is sp3 • Example: [NiC14]2 • The hybridisation scheme is shown in the following diagram. Orbitals ofNi2* ion sp3 hybridised orbitals of Ni2• 14]2. (hight-spin complex) sp3 hybrid Four pairs of electrons from 4Cl-

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Please find below the solution to the asked query:

Aufbau Principle should always be followed while writing electronic configuration. Transition metals are d block elements and include 3d, 4d and 5d shells of electrons.Unlike s and p block elements,in d block elements, electrons are added to the penultimate shell, expanding it from 8 to 18 electrons. In the atoms of these elements the outermost shell and the penultimate shell are incomplete.
General electronic configuration of transition metals is : (n-1)d^1-9ns^{0 or 1 or 2} 
The compound [NiCl₄]^2- , has sp³ hybridization which is determined as:

At step 1: we find the metal cation and as, x + (-4) = -2  or x = +2, So, metal ion is Ni²⁺ ion , whose configuration is 3d⁸ 

Step2 : Further, Cl, forms high spin complex , it could not pair up the unpaired electrons of 3d-orbital and so the four electrons pair donated by Cl-atoms are arranged in 4 sp³ hybridized orbitals.

The detailed mechanism is given as below:



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