Textbook Problem 9C.5

[michaelcrisera]

This problem states: Which of the following ligands can be polydentate? If the ligand can be polydentate, give the maximum number of places on the ligand that can bind simultaneously to a single metal center: a) HN(CH2HCH2NH2)2 b) CO3 2- c) H2O d) oxalate

I understand the concept of polydentate ligands, but I don't know how to determine the maximum number of places that the ligand can bond to a metal center. Can someone help explain this?

[Lauren Woodward 1I]

The max number of binding spots corresponds to the number of lone pairs present on different atoms. So H2O has two lone pairs, but they are present on the same atom (O), so it is monodentate. HN(CH2CH2NH2)2 has three lone pairs, and each one is on a different N atom, so it is tridentate. It's also important to note that the geometry of the molecule has to allow for rotation so multiple bonds can form. Single bonds are fairly flexible because they are formed when the ends of orbitals overlap. Other atoms require spacers between themself and a separate atom with a lone pair so that they can both form bonds with a single transition metal.