Which of the following complex is octahedral, diamagnetic and the most stable?
- K3[CO(CN)6]
- [Ni(NH3)6]Cl2
- The correct option is(A): Na3[COCl6]
- [Co(H2O)6]Cl2
The Correct Option is A
Solution and Explanation
To analyze the properties of K$_3$[Co(CN)$_6$], let's break it down:
Oxidation state of cobalt: The overall charge on the complex is 0. Let $x$ represent the oxidation state of cobalt: \[ 3 + x - 6 = 0 \implies x = +3 \] So, Co is in the +3 oxidation state.
Electronic configuration of \(Co^{3+}\): Cobalt's ground state is [Ar] \(3d^7 4s^2\).
After losing 3 electrons, the configuration becomes \(3d^6\).
Ligand strength: CN$^-$ is a strong field ligand (SFL) as per the spectrochemical series. Strong field ligands cause significant splitting of the d-orbitals, leading to pairing of electrons in the lower energy orbitals.
Electron pairing: In the presence of CN$^-$, the 3d electrons pair as follows: \[ \text{Before pairing: } \uparrow \uparrow \uparrow \uparrow \uparrow \uparrow \] \[ \text{After pairing: } \uparrow \downarrow \uparrow \downarrow \uparrow \downarrow \] As all electrons are paired, the complex is diamagnetic.
Geometry: The coordination number is 6, and with CN$^-$ being a strong ligand, the geometry is octahedral.
Stability: CN$^-$ forms strong bonds with the metal center due to its strong field nature, making K$_3$[Co(CN)$_6$] the most stable complex among the options.
Thus, K$_3$[Co(CN)$_6$] is octahedral, diamagnetic, and the most stable.
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