The molecule dimethylphosphinoethane [(CH₃)₂PCH₂CH₂P(CH₃)₂, which is abbreviated dmpe] is used as a ligand for some complexes that serve as catalysts. A complex that contains this ligand is Mo(CO)₄(dmpe) .
a. Draw the Lewis structure for dmpe, and compare it with ethylenediamine as a coordinating ligand.
b. What is the oxidation state of Mo in Na₂[Mo(CN)₂(CO)₂(dmpe)] ?
c. Sketch the structure of the [Mo(CN)₂(CO)₂(dmpe)]^2- ion, including all the possible isomers.

Verified step by step guidance

1. Step 1: To draw the Lewis structure for dimethylphosphinoethane (dmpe), start by identifying the central atoms and their connectivity. The molecule has two phosphorus atoms, each bonded to two methyl groups (CH3) and connected by an ethylene bridge (CH2-CH2).
2. Step 2: Compare dmpe with ethylenediamine (en), which is a bidentate ligand with two nitrogen donor atoms. Both dmpe and en can coordinate to a metal center through two donor atoms, but dmpe uses phosphorus atoms while en uses nitrogen atoms.
3. Step 3: To determine the oxidation state of Mo in Na2[Mo(CN)2(CO)2(dmpe)], assign typical oxidation states to the ligands: CN is -1, CO is neutral, and dmpe is neutral. The overall charge of the complex ion is -2.
4. Step 4: Set up the equation for the oxidation state of Mo: x + 2(-1) + 2(0) + 0 = -2, where x is the oxidation state of Mo. Solve for x.
5. Step 5: To sketch the structure of [Mo(CN)2(CO)2(dmpe)]2-, consider the possible geometric arrangements of the ligands around the Mo center. Explore different isomers by varying the positions of the CN and CO ligands, keeping in mind the coordination number and geometry of the metal center.

Key Concepts

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They help visualize the arrangement of electrons and the connectivity of atoms, which is crucial for understanding molecular geometry and reactivity. In the context of ligands like dimethylphosphinoethane, drawing the Lewis structure allows for the identification of donor atoms that can coordinate with metal centers.

Oxidation States

The oxidation state of an element in a compound indicates the degree of oxidation (loss of electrons) of that element. It is essential for determining the electron transfer processes in redox reactions and for understanding the coordination chemistry of metal complexes. In the case of the complex Na2[Mo(CN)2(CO)2(dmpe)], calculating the oxidation state of molybdenum (Mo) involves considering the charges of the ligands and the overall charge of the complex.

Isomerism in Coordination Compounds

Isomerism in coordination compounds refers to the existence of compounds with the same formula but different arrangements of atoms or ligands. This can include structural isomers, where the connectivity differs, and stereoisomers, where the spatial arrangement varies. Understanding isomerism is crucial for predicting the properties and reactivity of complexes like [Mo(CN)2(CO)2(dmpe)]2-, as different isomers can exhibit distinct chemical behaviors.