In this thrilling journey through coordination chemistry, we are tasked with determining the hybridization of six distinct coordination complexes and matching them to their corresponding orbital geometries. This is a classic test of your understanding of Valence Bond Theory (VBT) and Crystal Field Theory (CFT).
The Core Strategy
To conquer any hybridization problem in coordination chemistry, you must follow a strict, logical sequence:
1. Determine the Oxidation State: Find the charge on the central metal ion.
2. Write the Electronic Configuration: Know how many d-electrons you are working with.
3. Analyze the Ligand Strength: Is it a Strong Field Ligand (SFL) that forces pairing, or a Weak Field Ligand (WFL) that leaves electrons unpaired?
4. Assign the Hybridization: Based on the coordination number and the availability of inner d-orbitals, determine if the complex is inner orbital (d2sp3, dsp2) or outer orbital (sp3d2, sp3).
Let's break down each complex with surgical precision.
Analyzing the Octahedral Complexes
1. The Hexafluoroferrate Ion: [FeF6]4−
Here, iron is in a +2 oxidation state, giving it a 3d6 configuration. Fluoride (F−) is a notorious weak field ligand. It simply doesn't have the energetic muscle to force those d-electrons to pair up against their will. Since we need six empty orbitals for the octahedral geometry, and the inner 3d orbitals are occupied, we must look outward. We utilize one 4s, three 4p, and two 4d orbitals, resulting in an sp3d2 hybridization. This is an outer orbital complex.
2. The Titanium Complex: [Ti(H2O)3Cl3]
Titanium is in a +3 state, which means it has a highly sparse 3d1 configuration. With only one electron wandering around the 3d subshell, there are plenty of empty inner d-orbitals available. It effortlessly uses two of these inner 3d orbitals, leading to a d2sp3 hybridization.
3. The Hexaamminechromium Ion: [Cr(NH3)6]3+
Chromium in the +3 state has a 3d3 configuration. According to Hund's rule, these three electrons occupy the t2g orbitals singly. This naturally leaves exactly two eg orbitals completely empty! Therefore, regardless of the ligand's strength, Cr3+ will always utilize these inner orbitals, resulting in a d2sp3 hybridization.
Analyzing the Tetrahedral and Square Planar Complexes
4. The Tetrachloroferrate Ion: [FeCl4]2−
Iron is again in a +2 state (3d6). The coordination number is 4, and chloride (Cl−) is a weak field ligand. No pairing occurs. To accommodate four ligands, the metal uses one 4s and three 4p orbitals, giving us an sp3 hybridization, which corresponds to a tetrahedral geometry.
5. Nickel Tetracarbonyl: Ni(CO)4
This is a fascinating molecule! Nickel is in a rare 0 oxidation state, possessing a full 3d84s2 valence shell. However, carbonyl (CO) is an exceptionally strong field ligand and a powerful π-acceptor. It aggressively forces the two 4s electrons to migrate into the 3d subshell, pairing up with the existing electrons to create a completely full 3d10 configuration. With the 4s orbital now vacant, the complex utilizes the 4s and three 4p orbitals, resulting in an sp3 hybridization.
6. The Tetracyanonickelate Ion: [Ni(CN)4]2−
Here, nickel is in a +2 state, giving it a 3d8 configuration. Cyanide (CN−) is a strong field ligand. It forces the two unpaired electrons in the 3d subshell to pair up into a single orbital. This strategic pairing liberates exactly one 3d orbital. The complex seizes this opportunity, utilizing one 3d, one 4s, and two 4p orbitals to achieve a dsp2 hybridization, forming a beautiful square planar geometry.
The Final Match
With our analysis complete, the matching is straightforward:
- P (dsp2) perfectly matches with 6 ([Ni(CN)4]2−).
- Q (sp3) matches with both 4 ([FeCl4]2−) and 5 (Ni(CO)4).
- R (sp3d2) matches with 1 ([FeF6]4−).
- S (d2sp3) matches with both 2 ([Ti(H2O)3Cl3]) and 3 ([Cr(NH3)6]3+).
Mastering these electronic transitions and ligand effects is the key to unlocking the beautiful structural logic of coordination chemistry!