FZ2026: Elements of Organic and Inorganic Chemistry

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Shakir Alam UddinSuddin4@uclan.ac.ukFZ2026: ELEMENTS OFORGANIC ANDINORGANIC CHEMISTRYSemester 1: Assignment
Shakir UddinFZ2026: Elements of Organic and Inorganic Chemistry1)a)The distortion in given chemical formula is due to Jahn-Teller effect. The Jahn-Tellereffect describes that if the ground electronic configuration of a nonlinear complex isorbitally degenerate, and asymmetrically filled, then the complex distorts to removethe degeneracy and achieve a lower energy11.The oxidation state of Cr in Na4[(Cr(CN)6].10H2O is +2 i.e. Cr+2in a perfectlyoctahedral N-ligand environment has the ground state electronic configuration=t2g4Which represents the electronic arrangements as followsdxy2,dxz',diyz,dixy',dxz2,dxz'anddxy',dxz',dxz2of equal energy, because of the Jahn-Teller effect, the octahedralsymmetry of the complex will be automatically lowered to tetragonal symmetry tostabilize the complex8,9. This explains why in Na4[Cr(CN)6]·10H2O it was found thatthere were four Cr-C bonds at 2.066 Å and two Cr-C bonds at 1.936 Å. This is anexample of axial compressions distortion. There is a strong field due to CN-ligandsTo summarise, due to the two Cr-C bonds, which are axial, being shorter in length,the type of distortion is tetragonal compression9.1
Shakir UddinFZ2026: Elements of Organic and Inorganic Chemistryb)There is a strong field due to CN-ligands and thus a low spin. For Cr2+(d4) ion,tetragonal distortion involves, compression along the z-axis, hence electrons in thedxzand dyzorbitals will be repelled more by the ligand electrons than the electrons indxyorbitals. Hence energy of dxzand dyzwill be more than that of dxyorbitals6.2
Shakir UddinFZ2026: Elements of Organic and Inorganic Chemistryc)Normal Crystal field stabilisation energy, CFSE = 4(-2/5) = -8/5 + PETherefore, under the condition that this is distorted:Distorted Crystal Field Stabilisation Energy, CFSE= 2(-2/3) = -4/3And= 2(1/3) = 2/3So, the distorted CFCE = -4/3 + 2/3 = -2/33
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