أنواع وطبيعة التآصر في المركبات الكيمياوية (المركبات التناسقية )

2. أنواع وطبيعة التآصر في المركبات الكيمياوية (المركبات التناسقية ) The type and nature of bonding in chemical compounds (coordination compounds) أ.د. ماهر عبد الرزاق محمد

3. أنواع وطبيعة التآصر في المركبات الكيمياوية )المركبات التناسقية( • التآصر التساهمي (Covalent bonding) • التآصر الأيوني (Ionic bonding) • التآصر التناسقي (Coordination bonding)

4. التآصر التناسقي (Coordination bonding) • تآصر سيكما )- bonding(σ • تآصر باي)- bonding(π هنالك ثلاثة أنواع من أوربتالاتالليكاندات لتكوين أواصرباي )π) مع أوربتالاتd للفلز وهي : • أوربتالp عمودي على محور آصرة سيكما σ)) . • أوربتالd يقع في المستوي الذي يشتمل على ذرة الفلز . • آوربتال*π يقع في المستوي الذي يشتمل على ذرة الفلز.

5. Pi-bonding and MO Theory

6. تآصرπ بين أوربتالات d للفلز وأوربتالات الليكاند

7. Remember that pi-bonding is much weaker than sigma bonding, so this interaction simply perturbs the sigma MO diagram. Note that the (t2g)represents triple degeneracy, (eg) double degeneracy and (a) single degeneracy.

8. Example: [CoF6]3-

9. In the case of F-, the t2g orbitals are full with ligand electrons and they are lower than the metals because 2p orbitals are lower in energy than 3d and the electrons make them more electronegative. • As the ligand pi-orbitals overlap with the sigma orbitals of the metal, the F- orbitals raise the Co orbitals but the eg orbitals are un-affected

10. This means the bonding orbitals are mostly F- in character and the anti-bonding orbitals are mostly Co in character. This effectively decreases the 10Dqand thus F- is a weak ligand. Now look at pi-interactions of phosphine as a ligand (PR3). In phosphorous the 3d orbitals are empty so they are not very electronegative and thus are of higher energy compared to the metal sigma orbitals.

11. The same change in theorbital energies occurs butthis time the bonding t2g orbitals are mostly metal incharacter and they decreasein energy .

12. This effectively increases the 10Dq and thus the phosphine ligands are considered strong field ligands. Practical application and observations of MO Theory. The pi-bonding hypothesis can be corroborated by the IR stretch of CO. Remember, IR indicates the strength of the CO bond. The higher the wave number, the stronger bond.

13. For example, take the following complexes. [Mn1+(CO)6]1+ > [CrO(CO)6]0 > [V1-(CO)6]1- As the metal increases in electron density (i.e. reduced), then more electron density will be donated to the antibonding pi orbital of CO and the stretching frequency of CO will go down (i.e. weaker bond).

15. Trans-ligand pi competition

16. Thanks for your attention