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.^[1]

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(II), Pt(II), and Au(III). Examples with 2- and 3-coordination are common for Au(I), Cu(I), and Ag(I).

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.^{[2] [3]}

Homoleptic complexes

Homoleptic complexes (complexes with only chloride ligands) are often common reagents. Almost all examples are anions.

1st row

1st Transition Series

Complex	colour	electron config.	structure	geometry	comments
TiCl4	colourless	(t2g)0		tetrahedral
−	white/colourless	d0d0		face-sharing bioctahedron	Ti-Cl(terminal) = 2.23 Å, 2.45 (terminal) (N(PCl3)2)+ salt)[4]
3-	orange	(t2g)1(t2g)1		face-sharing bioctahedron	Ti-Ti =3.22 Å Ti-C1(terminal) = 2.32-2.35 Å, Ti-Cl(bridge) = 2.42-2.55 Å ((NEt4+)3)3 salt)[5]
2−	colourless	d0d0		bioctahedral
3-	green	(t2g)1(t2g)1(t2g)1		face-sharing trioctahedron	Ti-Ti = 3.19, 3.10 Å (terminal) Ti-C1(terminal) = 2.36 Å (terminal), Ti-Cl(bridge) = 2.50 Å ((PPh4+)3)3 salt)[6]
2−	yellow	d0		octahedral	PPh4+ salt Ti-Cl = 2.33 Å[7]
VCl4	red	(t2g)1		tetrahedral	V1−Cl = 2.29 Å
V2Cl10	violet	(t2g)0		edge-shared bioctahedron	V1−Cl(bridging) = 2.48 Å V1−Cl(terminal) = 2.16-2.21 Å[8]
2-	red	(t2g)1		octahedral	V1−Cl = 2.29 Å[9]
3−	pink[3]	(t2g)3		octahedral[10][3]
3−	red	(d3)2		face-sharing bioctahedron	Cr-Cl(terminal) = 2.31 Å, 2.42 (terminal) (Et2NH2+ salt)[11]
2−[12]	pale pink to while	(eg)2(t2g)3		tetrahedral	Mn-Cl bond length = 2.3731-2.3830 Å[13]
2−	dark red	(t2g)3(eg)1		octahedral	Mn-Cl distance = 2.28 Å K+ salt[14]) salt is isostructural with K2PtCl6
3−	brown[3]	(t2g)3(eg)1		octahedral[10][3]
2−	yellow-green	(eg)2(t2g)3		bitetrahedral	Mn-Cl(terminal) bond length = 2.24 Å Mn-Cl(terminal) bond length = 2.39 Å[15] (PPN+)2 salt
6−	pink	(t2g)3(eg)2		cofacial trioctahedron	Mn-Cl distance = --- Å +6 salt[16]
2−[12]	cream	(eg)3(t2g)3		tetrahedral((Et4N+)2 salt)[12]
−		(eg)2(t2g)3		tetrahedral	Fe-Cl bond length = 2.19 Å[17]
3−	orange	(t2g)3(eg)2		octahedral[3]
Fe2Cl62−	pale yellow	(eg)2(t2g)3		bitetrahedral	Fe-Cl(terminal) bond length = 2.24 Å Fe-Cl(terminal) bond length = 2.39 Å[15] (PPN+)2 salt
CoCl42−[12]	blue[12]	(eg)4(t2g)3		tetrahedral
Co2Cl62−	blue[15]	(eg)4(t2g)3		bitetrahedral	Mn-Cl(terminal) bond length = 2.24 Å Co-Cl(terminal) bond length = 2.35 Å[15] (PPN+)2 salt
NiCl42−[12]	blue[12]	(eg)4(t2g)4		tetrahedral	Ni-Cl bond length = 2.28 Å (Et4N+)2 salt[18]
Ni3Cl126−	orange[19]	(t2g)6(eg)2		confacial trioctahedral	((Me2NH2+)2)8 salt double salt with two Cl− Ni-Cl bond length = 2.36-2.38 Å[19]
CuCl42−[12]	orange[20] yellow (flattened tetrahedral)[21] green (square planar)[22]	(t2g)6(eg)3		flattened tetrahedral or square planar[23][24]	Cu-Cl bond length = 2.24 Å
Cu2Cl62−	red	(t2g)6(eg)32		edge-shared bis(square planar)[25]	Cu-Cl(terminal) = 2.24 Å Cu-Cl(bridging) = 2.31 Å
ZnCl42−	white/colorless	d10		tetrahedral

2nd rowedit

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

2nd Transition Series

Complex	colour	electron config.	structure	geometry	comments
ZrCl62−	yellow	d0		octahedral	Zr-Cl distance = 2.460 Å (Me4N+)2 salt[27]
Zr2Cl102−	colorless	(d0)2		edge-shared bioctahedral	Zr-Cl = 2.36 Å (terminal), 2.43 Å (bridging) N(PCl3)2)+ salt[4]
Nb2Cl10	yellow	(d0)2		edge-shared bioctahedral Nb2Cl10	3.99 Å[28]
NbCl6−	yellow	d0		octahedral	Nb-Cl = 2.34 Å N(PCl3)2)+ salt[4]
Nb6Cl182−	black	(d2)4(d3)2 (14 cluster electrons)		cluster Nb---Nb bonding	Nb-Cl = 2.92 Å (K+)2 salt[29]
MoCl6	black	d0		octahedron	Mo−Cl = 2.28 -2.31 Å[8]
MoCl62−	yellow	(t2g)2		octahedron	Mo−Cl = 2.37, 2.38, 2.27 Å[30]
MoCl63−	pink	(t2g)3		octahedral
Mo2Cl84−	purple[31]	2(d4)		Mo-Mo quadruple bond
Mo2Cl93−		2(d3)		face-shared bioctahedral	Mo-Mo (triple) bond length = 2.65 Å Mo-Cl (terminal) bond length = 2.38 Å Mo-Cl (bridging) bond length = 2.49 Å[32][33]
Mo2Cl10	green	(d1)2		edge-sharing bioctahedra[34]
Mo2Cl102−		(d2)2		edge-sharing bioctahedra[35]
Mo5Cl132−	brown[31]	d2d2d2d2d3		incomplete octahedron[36]
Mo6Cl142−	yellow	d4		octahedral cluster	(4-HOPyH+)2 salt[37]
TcCl62−	yellow	(t2g)3		octahedron	Tc-Cl = 2.35 Å for As(C6H5)4+ salt[38]
Tc2Cl82−	green	(t2g)4		Tc-Tc quadruple bond	Tc-Tc = 2.16, Tc-Cl = 2.34 Å for NBu4+ salt[39]
RuCl62−	brown	(t2g)4		octahedral	(EtPPh3+)2 salt[40]
Ru2Cl93−	red	(t2g)52		cofacial bioctahedral	Ru-Ru bond length = 2.71 Å; Ru-Cl(terminal) = 2.35 Å, Ru-Cl(bridging) = 2.36 Å ((Et4N)+)3 salt[41]
Ru3Cl124−	green	(d5)2(d6)		cofacial trioctahedral	Ru-Ru bond lengths = 2.86 Å Ru-Cl bond lengths = 2.37-2.39 Å (Et4N+)2(H7O3+)2 salt[42]
RhCl63−	red	(t2g)6		octahedral	H2N+(CH2CH2NH3+)2 salt)[43]
Rh2Cl93−	red-brown	(t2g)6		octahedral	Rh-Cl(terminal) = 2.30 Å, Rh-Cl(terminal) = 2.40 Å ((Me3CH2Ph)+)3 salt)[32]
PdCl42−	brown	d8		square planar
Pd2Cl62−[44]	red ((Et4N+)2 salt)	d8		square planar
Pd3Cl82−[45]	orange brown ((Bu4N+)2 salt)	d8		square planar
PdCl62−	brown	d6		octahedral	Pd(IV)
Pd6Cl12	yellow-brown	d8		square planar[46]
AgCl2−	white/colorless	d10		linear	salt of K(2.2.2-crypt)+[47]
CdCl42−	white/colorless	d10		tetrahedral	Et4N+ salt, Cd-Cl distance is 2.43 Å[26]
Cd2Cl62−	white/colorless	d10		edge-shared bitetrahedron	(C6N3(4-C5H4N)33+ salt[48]
Cd3Cl126−	white/colorless	d10		octahedral (central Cd) pentacoordinate (terminal Cd's) cofactial trioctahedral	(C6N3(4-C5H4N)33+ salt[48] (3,8-Diammonium-6-phenylphenanthridine3+)2[49]
Cd6Cl197−	white/colorless	d10		octahedron of octahedra	4,4'-(C6H3(2-Et)NH3+)2 salt[50]

3rd rowedit

Zdroj:https://en.wikipedia.org?pojem=Transition_metal_chloride_complex
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3rd Transition Series

Complex