TPR FL 2 #4 CP section

[akimhaneul]

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For this question, shouldn't the bond that forms between Cu2+ and H2O be ion-dipole interaction?

Why are they saying that it's coordinate covalent bond in the explanation? I thought it was a weak intermolecular interaction?

 

[aldol16]

Why are they saying that it's coordinate covalent bond in the explanation? I thought it was a weak intermolecular interaction?

You should know that water (and other solvents) are often coordinated to metal centers and serve as dative ligands. The aqua ligand is quite common and is sometimes omitted for clarity because it does not often participate in catalysis - sometimes it just serves to donate more electron density towards the metal center.

 

[akimhaneul]

You should know that water (and other solvents) are often coordinated to metal centers and serve as dative ligands. The aqua ligand is quite common and is sometimes omitted for clarity because it does not often participate in catalysis - sometimes it just serves to donate more electron density towards the metal center.

Thank you! I am wondering why this strong coordinate covalent bond occurs instead of just weak intermolecular force? Does it happen for no special reason?


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[aldol16]

Thank you! I am wondering why this strong coordinate covalent bond occurs instead of just weak intermolecular force? Does it happen for no special reason?

Well, it happens because Cu(II) is mildly Lewis acidic and water can be mildly Lewis basic (coordination bonds are, by convention, conceived as Lewis basic ligands coordinating to Lewis acidic metals). They are not particularly strong - especially metal-aqua bonds. Weak and strong are relative though - weak relative to what?

 

[akimhaneul]

Well, it happens because Cu(II) is mildly Lewis acidic and water can be mildly Lewis basic (coordination bonds are, by convention, conceived as Lewis basic ligands coordinating to Lewis acidic metals). They are not particularly strong - especially metal-aqua bonds. Weak and strong are relative though - weak relative to what?

Well shouldn't the coordinate covalent bond that is formed in this question be pretty strong compared to weak intermolecular forces such as hydrogen bonding, van der waals, and ion dipole forces etc since it actually involves transfer of electrons?

 

[aldol16]

Well shouldn't the coordinate covalent bond that is formed in this question be pretty strong compared to weak intermolecular forces such as hydrogen bonding, van der waals, and ion dipole forces etc since it actually involves transfer of electrons?

There's no transfer of electrons. In this case, you have aqua ligands on a copper center and since the aqua ligands, by convention, act as Lewis bases, already have two electrons to donate, there's no need to oxidize the metal center. In other words, the ligand is labile and the bond is more ionic in nature than covalent and there's no real transfer of electrons. In ligand field theory, the electrons "belong" to the ligands. You can almost imagine it as electrostatic forces (which they are) with the ligands being negative point charges oriented around a positive point charge, aka the metal center.