I have rarely seen any chromium $(\ce{Cr})$ square planar complexes and I have been told that $\ce{[Cr(CN)4]-}$ is tetrahedral.
So, if the statement is actually correct, are there any other known examples of square planar complexes of chromium?
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Sign up to join this communityI have rarely seen any chromium $(\ce{Cr})$ square planar complexes and I have been told that $\ce{[Cr(CN)4]-}$ is tetrahedral.
So, if the statement is actually correct, are there any other known examples of square planar complexes of chromium?
This doesn't appear to be a rare case and there are plenty $\ce{Cr^2+}$ square planar complexes. I found 15 square planar complexes with well-determined crystal structures $(R_\mathrm{int} < 10\%)$ by applying the following geometrical restrains:
CCDC ACACCS [1] bis(2,4-Pentanedionato)-chromium(II)
CCDC BHPZCR [2] bis(Dihydro-bis(1-pyrazolyl)borato) chromium(II)
CCDC CRPORT [3] α,β,γ,δ-Tetraphenylporphinato-chromium(II) toluene solvate
CCDC DAQDUV [4] hexakis(Tetrahydrofuran)-magnesium tetrakis(perfluorophenyl)-chromium(II) tetrahydrofuran solvate
CCDC DAYNEW [5] bis(Pyridinium) diaqua-dibromo-chromium(II) dibromide
CCDC EGINEN [6] bis((μ2-Chloro)-hexakis(tetrahydrofuran)-di-lithium) tetrakis(pentachlorophenyl)-chromium(II)
CCDC EQIVOP [7] trans-Dichloro-bis(2,6-dimethylpyridine)-chromium(II)
CCDC HARKIU [8] trans-bis(tris(t-Butoxy)siloxy)-bis(diethylammonio)-chromium(II)
CCDC KOMRAF [9] Tetrapyridine-chromium(II) bis(hexafluorophosphate) dipyridine clathrate
CCDC PITVAP [10] bis(Tetra-n-butylammonium) tetrakis(isothiocyanato)-chromium(II)
CCDC PUQPEY [11] bis(1-t-butyl-3-(di-t-butylphosphino)imidazol-2-ylidene)-dichloro-chromium
CCDC PUQPIC [11] dichloro-bis(1-(di-t-butylphosphino)-3-mesitylimidazol-2-ylidene)-chromium tetrahydrofuran solvate
CCDC PUQPIC [12] bis((Phenothiazinyl-N)-tetrahydrofuran)-chromium(II)
CCDC XEBZAF [13] trans-bis(4-t-Butylpyridine)-dichloro-chromium(II)
CCDC ZOYCUL [14] Dichloro-bis((trimethylphosphine)trimethylsilylamido)-chromium(II)
An article by Bradley et al. [1] documents $\ce{[Cr(N(SiMe3)2)2(THF)2]}$ as a square planar complex. However, the $\ce{[Cr(N(SiMe3)2)3NO]}$ complex is pseudotetrahedral $(C_\mathrm{3v}).$
Figures below are provided by andselisk, the are from the reference above.