`=>` The magnetic moment of coordination compounds can be measured by the magnetic susceptibility experiments.
`=>` The results can be used to obtain information about the structures adopted by metal complexes.
`=>` For metal ions with upto three electrons in the `color{red}(d)`-orbitals, like `color{red}(Ti^(3+), (d^1); V^(3+) (d^2); Cr^(3+), (d^3))`; two vacant `color{red}(d)`-orbitals are available for octahedral hybridisation with `color{red}(4s)` and `color{red}(4p)` orbitals.
● The magnetic behaviour of these free ions and their coordination entities is similar.
`=>` When more than three `color{red}(3d)` electrons are present, the required pair of `color{red}(3d)` orbitals for octahedral hybridisation is not directly available (as a consequence of Hund’s rule).
● Thus, for `color{red}(d^4 , (Cr^(2+), Mn^(3+)), d^5 (Mn^(2+), Fe^(3+)), d^6 (Fe^(2+), Co^(3+)))` cases, a vacant pair of `color{red}(d)` orbitals results only by pairing of `color{red}(3d)` electrons which leaves two, one and zero unpaired electrons, respectively.
`=>` The magnetic data agree with maximum spin pairing in many cases, especially with coordination compounds containing `color{red}(d^6)` ions.
`=>` However, with species containing `color{red}(d^4)` and `color{red}(d^5)` ions there are complications.
`=>` `color{red}([Mn(CN)_6]^(3-))` has magnetic moment of two unpaired electrons while `color{red}([MnCl_6]^(3-))` has a paramagnetic moment of four unpaired electrons.
● `color{red}([Fe(CN)_6]^(3-))` has magnetic moment of a single unpaired electron while `color{red}([FeF_6]^(3-))` has a paramagnetic moment of five unpaired electrons.
● `color{red}([CoF_6]^(3-))` is paramagnetic with four unpaired electrons while `color{red}([Co(C_2O_4)_3]^(3-))` is diamagnetic.
`=>` This apparent anomaly is explained by valence bond theory in terms of formation of inner orbital and outer orbital coordination entities.
● `color{red}([Mn(CN)_6]^(3-), [Fe(CN)_6]^(3-))` and `color{red}([Co(C_2O_4)_3]^(3-))` are inner orbital complexes involving `color{red}(d^2sp^3)` hybridisation, the former two complexes are paramagnetic and the latter diamagnetic.
● On the other hand, `color{red}([MnCl_6]^(3-), [FeF_6]^(3-))` and `color{red}([CoF_6-]^(3-))` are outer orbital complexes involving `color{red}(sp^3d^2)` hybridisation and are paramagnetic corresponding to four, five and four unpaired electrons.
`=>` The magnetic moment of coordination compounds can be measured by the magnetic susceptibility experiments.
`=>` The results can be used to obtain information about the structures adopted by metal complexes.
`=>` For metal ions with upto three electrons in the `color{red}(d)`-orbitals, like `color{red}(Ti^(3+), (d^1); V^(3+) (d^2); Cr^(3+), (d^3))`; two vacant `color{red}(d)`-orbitals are available for octahedral hybridisation with `color{red}(4s)` and `color{red}(4p)` orbitals.
● The magnetic behaviour of these free ions and their coordination entities is similar.
`=>` When more than three `color{red}(3d)` electrons are present, the required pair of `color{red}(3d)` orbitals for octahedral hybridisation is not directly available (as a consequence of Hund’s rule).
● Thus, for `color{red}(d^4 , (Cr^(2+), Mn^(3+)), d^5 (Mn^(2+), Fe^(3+)), d^6 (Fe^(2+), Co^(3+)))` cases, a vacant pair of `color{red}(d)` orbitals results only by pairing of `color{red}(3d)` electrons which leaves two, one and zero unpaired electrons, respectively.
`=>` The magnetic data agree with maximum spin pairing in many cases, especially with coordination compounds containing `color{red}(d^6)` ions.
`=>` However, with species containing `color{red}(d^4)` and `color{red}(d^5)` ions there are complications.
`=>` `color{red}([Mn(CN)_6]^(3-))` has magnetic moment of two unpaired electrons while `color{red}([MnCl_6]^(3-))` has a paramagnetic moment of four unpaired electrons.
● `color{red}([Fe(CN)_6]^(3-))` has magnetic moment of a single unpaired electron while `color{red}([FeF_6]^(3-))` has a paramagnetic moment of five unpaired electrons.
● `color{red}([CoF_6]^(3-))` is paramagnetic with four unpaired electrons while `color{red}([Co(C_2O_4)_3]^(3-))` is diamagnetic.
`=>` This apparent anomaly is explained by valence bond theory in terms of formation of inner orbital and outer orbital coordination entities.
● `color{red}([Mn(CN)_6]^(3-), [Fe(CN)_6]^(3-))` and `color{red}([Co(C_2O_4)_3]^(3-))` are inner orbital complexes involving `color{red}(d^2sp^3)` hybridisation, the former two complexes are paramagnetic and the latter diamagnetic.
● On the other hand, `color{red}([MnCl_6]^(3-), [FeF_6]^(3-))` and `color{red}([CoF_6-]^(3-))` are outer orbital complexes involving `color{red}(sp^3d^2)` hybridisation and are paramagnetic corresponding to four, five and four unpaired electrons.