Coordination numbers?

Question

Can some one tell me how to find the coordination nubers for the tranistion elements in the following compounds? I'm not intersted so much in the answer as how to get the coordinaion numbers!

Cr(en)2(C2O4)+

[Au(en)2]Cl3

Answer 1

OK, if [Au(en)2]Cl3 is a neutral species, ie no charge, then if you remove the Cl3, which has a charge of 3-, the [Au(en)2] has a charge of 3+.  Ethylenediamine (en) is a neutral bidentate ligand, so it does not effect the charge of the overall structure, thus the gold is Au 3+, ie has a coordination number of 3.

Answer 2

The coordination number of a chemical compound is the total number of atoms connected directly to the central atom (e.g. transition elements). Since "en" and "C2O4" are bidentate ligands, so in each case two atoms will be involved in direct bonding with transition metal and, therefore, Cr and Au complexes have 6 and 4 coordination numbers, respectively.