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Halogen bonding in salts of ortho-halogenpyridines and hexacyanocobaltate(III) acid

Cyanometallate anions such as hexacyanoferrate or hexacyanocobaltate are Lewis bases and are therefore good hydrogen [1] and halogen bond [2] acceptors. Protonated cyanometallate anions, such as hexacyanoferrates, are good hydrogen bond donors.[3] Protonated hexacyanoferrates have recently also been studied as potential halogen bond donors.[4] To the best of our knowledge, no similar studies have been performed with other protonated cyanometallates to date. In this work we have used hexacyanocobaltate(III) acid (H3[Co(CN)6]) with 2-chloropyridine (2-Clpy), 2- bromopyridine (2- Brpy) and 2-iodopyridine (2-Ipy) to synthetize three salts. In all three cases I∙∙∙N halogen bonds and N-H∙∙∙N hydrogen bonds are present, along with O-H∙∙∙N hydrogen bonds between the anions and Zundel (H5O2+) cations. The anion is completely deprotonated in all three salts. 2- Clpy and 2-Brpy salts are isostructural, while the 2-Ipy salt contains a tetramer of water molecules bridging six hexacyanocobaltate(III) anions and two 2-IpyH cations. [1] B. Yan, H. D. Wang, Z. D. Chen, J. Mol. Struct., 569 (2001) 65. [2] J. E. Ormond-Prout, P. Smart, L. Brammer, Cryst. Growth. Des., 12 (2012) 205. [3] I. Cvrtila, V. Stilinović, Cryst. Growth Des., 17 (2017) 6793. [4] N. Jakupec, L. Fotović, V. Stilinović, CrystEngComm, 22 (2020) 8142.

halogen bond ; salt ; ortho-halogenpyridines ; hexacyanocobaltate(III) acid

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