Transition metal chloride complex

In chemistry, a transition metal chloride complex is a coordination complex that consists of a transition metal coordinated to one or more chloride ligand. The class of complexes is extensive.

Bonding

Halides are X-type ligands in coordination chemistry. They are both σ- and π-donors. Chloride is commonly found as both a terminal ligand and a bridging ligand. The halide ligands are weak field ligands. Due to a smaller crystal field splitting energy, the homoleptic halide complexes of the first transition series are all high spin. Only ³⁻ is exchange inert.
Homoleptic metal halide complexes are known with several stoichiometries, but the main ones are the hexahalometallates and the tetrahalometallates. The hexahalides adopt octahedral coordination geometry, whereas the tetrahalides are usually tetrahedral. Square planar tetrahalides are known for Pd, Pt, and Au. Examples with 2- and 3-coordination are common for Au, Cu, and Ag.
Due to the presence of filled p_π orbitals, halide ligands on transition metals are able to reinforce π-backbonding onto a π-acid. They are also known to labilize cis-ligands.

Homoleptic complexes

Homoleptic complexes are often common reagents. Almost all examples are anions.

1st row

2nd row

Some homoleptic complexes of the second row transition metals feature metal-metal bonds.

Complex	colour	electron config.	structure	geometry	comments
²⁻	yellow	d⁰		octahedral	Zr-Cl distance = 2.460 Å ₂ salt
²⁻	colorless	²		edge-shared bioctahedral	Zr-Cl = 2.36 Å, 2.43 Å N⁺ salt
Nb₂Cl₁₀	yellow	²		edge-shared bioctahedral	3.99 Å
⁻	yellow	d⁰		octahedral	Nb-Cl = 2.34 Å N⁺ salt
²⁻	black	⁴²		cluster Nb---Nb bonding	Nb-Cl = 2.92 Å 2 salt
MoCl₆	black	d⁰		octahedron	Mo−Cl = 2.28 -2.31 Å
²⁻	yellow	²		octahedron	Mo−Cl = 2.37, 2.38, 2.27 Å
³⁻	pink	³		octahedral
Potassium octachlorodimolybdate\|⁴⁻	purple	2		Mo-Mo quadruple bond
³⁻		2		face-shared bioctahedral	Mo-Mo bond length = 2.65 Å Mo-Cl bond length = 2.38 Å Mo-Cl bond length = 2.49 Å
Mo₂Cl₁₀	green	₂		edge-sharing bioctahedra	-
²⁻		₂		edge-sharing bioctahedra	-
²⁻	brown	d²d²d²d²d³		incomplete octahedron
Molybdenum chloride\|²⁻	yellow	d⁴		octahedral cluster	₂ salt
²⁻	yellow	³		octahedron	Tc-Cl = 2.35 Å for As₄⁺ salt
²⁻	green	⁴		Tc-Tc quadruple bond	Tc-Tc = 2.16, Tc-Cl = 2.34 Å for NBu₄⁺ salt
²⁻	brown	⁴		octahedral	₂ salt
³⁻	red	₂		cofacial bioctahedral	Ru-Ru bond length = 2.71 Å; Ru-Cl = 2.35 Å, Ru-Cl = 2.36 Å ₃ salt
⁴⁻	green	₂		cofacial trioctahedral	Ru-Ru bond lengths = 2.86 Å Ru-Cl bond lengths = 2.37-2.39 Å ₂₂ salt
³⁻	red	⁶		octahedral	H₂N⁺
³⁻	red-brown	⁶		octahedral	Rh-Cl = 2.30 Å, Rh-Cl = 2.40 Å ₃ salt)
²⁻	brown	d⁸		square planar
²⁻	red	d⁸		square planar
²⁻	orange brown	d⁸		square planar
²⁻	brown	d⁶		octahedral	Pd
	yellow-brown	d⁸		square planar
⁻	white/colorless	d¹⁰		linear	salt of ⁺
²⁻	white/colorless	d¹⁰		tetrahedral	Et₄N⁺ salt, Cd-Cl distance is 2.43 Å
²⁻	white/colorless	d¹⁰		edge-shared bitetrahedron	₃³⁺ salt
⁶⁻	white/colorless	d¹⁰		octahedral pentacoordinate cofactial trioctahedral	₃³⁺ salt ₂
⁷⁻	white/colorless	d¹⁰		octahedron of octahedra	4,4'-₂ salt

3rd row

Complex	colour	electron config.	structure	geometry	comments
²⁻	white	d⁰		octahedral	Hf-Cl distance = 2.448 A
²⁻	colorless/white	d⁰		edge-shared bioctahedral
⁻	colorless/white
^2-	green	d⁰		octahedral	Ta-Ta = 2.34 Å ²	octahedral	W-Cl distances range from 2.34 to 2.37 Å
⁻		¹		octahedral	W-Cl distance = 2.32 Å
W₂Cl₁₀	black	₂		bioctahedral	W-W distance = 3.814 Å
⁴⁻	blue	2		W-W quadruple bond	dW-W = 2.259 Å ₄ salt
²⁻		d³d²		face-sharing bioctahedral	W-W distance = 2.54 Å W-Cl = 2.36 Å, W-Cl = 2.45 Å
³⁻		d³d³		octahedral	W-Cl distance = 2.32 Å
³⁻		d³,d³,d⁴		^3-	W-W distances = 2.84 Å
²⁻		d³,d⁴,d⁴		^2-	W-W distances = 2.78 Å
^2-	yellow	₆		see Mo₆Cl₁₂
⁻	red-brown	²		octahedral	Re-Cl distance = 2.24-2.31 Å
Rhenium chloride\|		¹		octahedral	Re-Cl distance = 2.263 Å
²⁻	green	³		octahedral	Re-Cl distance = 2.35-2.38 Å
²⁻		³⁴		face-sharing bioctahedral	Re-Re distance = 2.48 Å Re-Cl distances = 2.42 Å, 2.33 Å
⁻		₂		face-sharing bioctahedral	Re-Re distance = 2.70 Å Re-Cl distances = 2.41, 2.28 Å
⁻	dark green	³		octahedral	d_Os-Cl = 2.30 Å for Et₄N⁺ and Ph₄P⁺ salts
²⁻	yellow-orange	⁴		octahedral	Os-Cl distance 2.33 Å
²⁻	green	₂		square antiprism	d_Os-Os = 2.182 Å, d_Os-Cl = 2.32 Å ₂ salt
²⁻	green	₂		octahedral	d_Os-Cl = 2.30 Å d_Os-Cl = 2.42 Å ₂ salt
³⁻	red	⁶		octahedral	Ir-Cl = 2.36 Å
²⁻	brown	⁵		octahedral	Ir-Cl = 2.33 Å
³⁻	-	₂		bi-octahedral
²⁻	pink	d⁸		square planar
²⁻	yellow	d⁶		octahedral	Pt-Cl distance = 2.32 Å Et₄N⁺ salt,
⁻	red	₂		octahedral	Pt-Cl_t and Pt-Cl_bridge = 2.25, 2.38 Å
²⁻	yellow-brown	₂		edge-shared bioctahedral	Pt-Cl_t and Pt-Cl_bridge = 2.27, 2.37 Å
	yellow-brown	₆		square planar	Pt-Cl = 2.31
⁻	white/colorless	d¹⁰		linear	Au-Cl distances of 2.28 Å NEt₄⁺ salt
Gold chloride\|	black	₂₂		linear and square planar	rare example of mixed valence, molecular chloride
⁻	yellow	d⁸		square planar	Au-Cl distances of 2.26 Å NBu₄⁺ salt
²⁻	white/colorless	d¹⁰		tetrahedral	Hg-Cl distance is 2.46 Å Et₄N⁺ salt
²⁻	white/colorless	d¹⁰		edge-shared bitetrahedral	Hg-Cl distance is 2.46 Å Bu₄N⁺ salt