What is the coordination number of the metal in each of the following complexes? (a) [Ni(CN)5]3- (b) Ni(CO)4 (c) [Co(en)2(H2O)Br]2+ (d) [Cu(H2O)2(C2O4)2]2- (e) Co(NH3)3(NO2)3

Verified step by step guidance

Step 1: Understand the concept of coordination number. The coordination number of a metal in a complex is the number of ligand donor atoms to which the metal is directly bonded.

Step 2: Analyze complex (a) [Ni(CN)_5]^{3-}. Identify the ligands and count the number of CN^- ligands bonded to Ni. Each CN^- ligand donates one pair of electrons to the metal.

Step 3: Analyze complex (b) Ni(CO)_4. Identify the ligands and count the number of CO ligands bonded to Ni. Each CO ligand donates one pair of electrons to the metal.

Step 4: Analyze complex (c) [Co(en)_2(H_2O)Br]^{2+}. Identify the ligands: ethylenediamine (en) is a bidentate ligand, meaning it donates two pairs of electrons, while H_2O and Br^- are monodentate ligands.

Step 5: Analyze complex (d) [Cu(H_2O)_2(C_2O_4)_2]^{2-}. Identify the ligands: oxalate (C_2O_4^{2-}) is a bidentate ligand, and H_2O is a monodentate ligand. Count the total number of donor atoms.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Coordination Number

The coordination number refers to the number of ligand atoms that are directly bonded to a central metal atom in a coordination complex. It is a crucial concept in coordination chemistry, as it helps determine the geometry and stability of the complex. For example, in [Ni(CN)5]3-, the coordination number is 5, indicating that five cyanide ligands are coordinated to the nickel ion.

Ligands

Ligands are ions or molecules that can donate a pair of electrons to a central metal atom to form a coordination complex. They can be classified as monodentate, bidentate, or polydentate based on the number of donor atoms they possess. Understanding the nature of ligands is essential for determining the coordination number and the overall structure of the complex, as seen in complexes like Ni(CO)4, where carbon monoxide acts as a monodentate ligand.

Oxidation State

The oxidation state of a metal in a coordination complex is the charge that the metal would have if all ligands were removed along with their bonding electrons. It is important for understanding the electronic properties and reactivity of the complex. For instance, in [Co(en)2(H2O)Br]2+, the cobalt has a specific oxidation state that influences its coordination number and the overall charge of the complex.

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