# Has a low spin tetrahedral Ni(II) complex been synthesised?

How can $$\ce{Ni(II)}$$ form a low spin tetrahedral compound? I was not able to find such compounds.

$$\ce{Ni(II)}$$ will have $$\mathrm {4s^03d^8}$$ and tetrahedral needs $$\mathrm{sp^3}$$. So $$2$$ electrons will always be unpaired. Is a rare case possible?

I am only aware of hybridisation theory and basic CFT theory for complexes.

• Tetrahedral complexes are always high spin. Only exception I recall would be tetrakis-(1-norbonyl)cobalt(IV) – Aniruddha Deb Sep 8 '20 at 13:25
• Don't use hybridisation for transition metal complexes... – orthocresol Sep 8 '20 at 13:38
• @orthocresol your own answer should be relevant here: chemistry.stackexchange.com/questions/115051/… – Nilay Ghosh Sep 8 '20 at 14:09
• @NilayGhosh i want to know if a LOW SPIN tetrahedral Nickel complex has been made. I am aware of the square planar nickel compounds and high spin Nickel tetrahedral. – Shaurya Goyal Sep 9 '20 at 5:17

You asked two different questions in your title and the text body of the post. I wasn't sure which one is you meant to know. However, orthocresol has explained the question about low spin tetrahedral compounds: Why are low spin tetrahedral complexes so rare?. He also explain "Why it is wrong to use the concept of hybridization for transition metal complexes."

About your question in the title: "Has a tetrahedral $$\ce{Ni(II)}$$ complex been synthesized?"

Answer is "yes." Orthocresol has given common example here, which is $$\ce{NiCl4^2-}$$. There are also non-common tetrahedral $$\ce{Ni(II)}$$ complexes have been synthesized. For instance, a series of $$\ce{[(C2H5)3PO]2NiX2}$$ where $$\ce{X = Cl, Br, I}$$ has been synthesized by Cotton and Goodgame (Ref.1; yes, that is the same Cotton in Cotton and Wilkinson):

The $$\ce{Ni(II)}$$ complexes $$\ce{[(C2H5)3PO]2NiX2}$$ where $$\ce{X = Cl, Br,}$$ and $$\ce{I}$$ have been prepared. Their physical properties, especially their electronic spectra and high magnetic moments, leave little doubt that the nickel ion in each case surrounded by two oxygen atom and two halogen atoms in an essentially tetrahedral array.

In addition, some distorted-tetrahedral nickel(II) complexes (Ref.2) and some pseudo-tetrahedral nickel(II) complexes (Ref.3) have been prepared as well.

References:

1. F. Albert Cotton, David M. L. Goodgame, "New Tetrahedral Complexes of Nickel(II)," J. Am. Chem. Soc. 1960, 82(22), 5771–5774 (https://doi.org/10.1021/ja01507a001).
2. S. Trofimenko, J. C. Calabrese, J. K. Kochi, S. Wolowiec, F. B. Hulsbergen, J. Reedijk, "Spectroscopic analysis, coordination geometry, and X-ray structures of nickel(II) compounds with sterically demanding tris(pyrazolyl)borate ligands and azide or (thio)cyanate anions. Crystal and molecular structures of bis[($$\mu$$-thiocyanato-N,S)(hydrotris(3-isopropyl-4-bromopyrazol-1-yl)borato)nickel(II)]-3-heptane and (thiocyanato-N)(hydrotris(3-tert-butyl-5-methylpyrazol-1-yl)borato)nickel(II)," Inorg. Chem. 1992, 31(19), 3943–3950 (https://doi.org/10.1021/ic00045a017).
3. John T. Donoghue, Russell S. Drago, "Non-aqueous Coördination Phenomena-Complexes of Hexamethyl-phosphoramide. II. Pseudo-tetrahedral Complexes of Nickel(II) and Cobalt(II)," Inorg. Chem. 1963, 2(3), 572–576 (https://doi.org/10.1021/ic50007a036).
• I think OP is looking for "low-spin tetrahedral complex of nickel". Such complexes are already rare in itself and I don't know if such complex exist for nickel. The first such complex observed is cobalt norboryl complex which Aniruddha pointed out. Other new examples is a new Co(II) complex which is a low-spin complex with a distorted tetrahedral geometry and a chromium complex. I have added those as a update in the comment section of ortho's previous answer. – Nilay Ghosh Sep 9 '20 at 3:39
• I wanted to know if any LOW SPIN NICKEL TETRAHEDRAL complexes exist. Just specific for nickel. – Shaurya Goyal Sep 9 '20 at 5:18
• I'm not sure I can find one for you. One of given references said it is very rare. – Mathew Mahindaratne Sep 9 '20 at 6:38