chemistry coordinate number problem

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#1
How would you tell the coordinate number of PR? We know that it's a multidentate ligand, but not the coordinate number specifically. If we look at it's reaction with iron, it substitutes 4H2O molecules. But this doesn't tell you straight away the coordinate number, because (for example) Cu(H2O)6^2+ and Cl- ions react to make CuCl4^2- + 6H2O molecules. This doesn't mean each Cl molecule has a coordination number of 6/4.

I assume that it's a balance between charge and the actual moles of products that will tell us? Since PR replaces 4 H2O molecules, but it hasn't changed the charge of the overall complex, we can infer that it has a coordinate number of 4 right?

I honestly don't really know if it's correct or not, I just wanted to double check to make sure the method for working out a question like this.

Thanks for any help in advance
0
9 months ago
#2
(Original post by pondering-soul)
How would you tell the coordinate number of PR? We know that it's a multidentate ligand, but not the coordinate number specifically. If we look at it's reaction with iron, it substitutes 4H2O molecules. But this doesn't tell you straight away the coordinate number, because (for example) Cu(H2O)6^2+ and Cl- ions react to make CuCl4^2- + 6H2O molecules. This doesn't mean each Cl molecule has a coordination number of 6/4.

I assume that it's a balance between charge and the actual moles of products that will tell us? Since PR replaces 4 H2O molecules, but it hasn't changed the charge of the overall complex, we can infer that it has a coordinate number of 4 right?

I honestly don't really know if it's correct or not, I just wanted to double check to make sure the method for working out a question like this.

Thanks for any help in advance
Most of the time, if a multidentate ligand replaces n water molecules from a hexaaqua complex then it will be n coordinate (although there are always exceptions). If you look up the structure of porphyrin you can see that it is always a 4 coordinate ligand through its nitrogens.
1
8 months ago
#3
(Original post by pondering-soul)
How would you tell the coordinate number of PR? We know that it's a multidentate ligand, but not the coordinate number specifically. If we look at it's reaction with iron, it substitutes 4H2O molecules. But this doesn't tell you straight away the coordinate number, because (for example) Cu(H2O)6^2+ and Cl- ions react to make CuCl4^2- + 6H2O molecules. This doesn't mean each Cl molecule has a coordination number of 6/4.

I assume that it's a balance between charge and the actual moles of products that will tell us? Since PR replaces 4 H2O molecules, but it hasn't changed the charge of the overall complex, we can infer that it has a coordinate number of 4 right?

I honestly don't really know if it's correct or not, I just wanted to double check to make sure the method for working out a question like this.

Thanks for any help in advance
The equation:

PR + [Fe(H2O)6]2+ --> [FePr(H2O)2]2+ 4H2O

shows you that the PR must form 4 coordinate bonds to the Fe2+ as it displaces 4 water ligands. The fe2+ thus still has a coordination number of 6 in the [FePr(H2O)2]2+ and so must be an octahedral shape
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