Indicate the likely coordination number of the metal in each of the following complexes: (a) \(\left[\mathrm{Rh}(\text { bipy })_{3}\right]\left(\mathrm{NO}_{3}\right)_{3}\) (b) \(\mathrm{Na}_{3}\left[\mathrm{Co}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2} \mathrm{Cl}_{2}\right]\) (c) \(\left[\mathrm{Cr}(o \text { -phen })_{3}\right]\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{3}\) (d) \(\mathrm{Na}_{2}[\mathrm{Co}(\mathrm{EDTA}) \mathrm{Br}]\)

For each complex, identify the central metal atom and the surrounding ligands that are bonded to the metal. (a) In \(\left[\mathrm{Rh}(\text{bipy})_{3}\right]\left(\mathrm{NO}_{3}\right)_{3}\), the metal is Rh and the ligands are bipy (bipyridine), which has a coordination number of 2 per ligand. (b) In \(\mathrm{Na}_{3}\left[\mathrm{Co}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{2} \mathrm{Cl}_{2}\right]\), the metal is Co and the ligands are \(\mathrm{C}_{2}\mathrm{O}_{4}\) (oxalate) with a coordination number of 2 per ligand, and \(\mathrm{Cl}\) with a coordination number of 1. (c) In \(\left[\mathrm{Cr}(o\text{-phen})_{3}\right]\left(\mathrm{CH}_{3}\mathrm{COO}\right)_{3}\), the metal is Cr and the ligands are o-phen (ortho-phenanthroline), which has a coordination number of 2 per ligand. (d) In \(\mathrm{Na}_{2}[\mathrm{Co}(\mathrm{EDTA}) \mathrm{Br}]\), the metal is Co, and the ligands are EDTA (ethylenediaminetetraacetic acid) with a coordination number of 6, and Br with a coordination number of 1.

Multiply the coordination number of each ligand with the number of times the ligand is bound to the metal and add them together to find the overall coordination number of the metal. (a) For \(\left[\mathrm{Rh}(\text{bipy})_{3}\right]\left(\mathrm{NO}_{3}\right)_{3}\): Rh has 3 bipy ligands, each contributing 2. \\ Coordination number = 3 × 2 = 6 (b) For \(\mathrm{Na}_{3}\left[\mathrm{Co}\left(\mathrm{C}_{2}\mathrm{O}_{4}\right)_{2} \mathrm{Cl}_{2}\right]\): Co has 2 \(\mathrm{C}_{2}\mathrm{O}_{4}\) ligands, each contributing 2, and 2 \(\mathrm{Cl}\) ligands, each contributing 1. \\ Coordination number = (2 × 2) + (2 × 1) = 6 (c) For \(\left[\mathrm{Cr}(o\text{-phen})_{3}\right]\left(\mathrm{CH}_{3}\mathrm{COO}\right)_{3}\): Cr has 3 o-phen ligands, each contributing 2. \\ Coordination number = 3 × 2 = 6 (d) For \(\mathrm{Na}_{2}[\mathrm{Co}(\mathrm{EDTA}) \mathrm{Br}]\): Co has 1 EDTA ligand, contributing 6, and 1 Br ligand, contributing 1. \\ Coordination number = 6 + 1 = 7 So, the coordination numbers for the metals in each complex are: (a) Rh: 6 (b) Co: 6 (c) Cr: 6 (d) Co: 7