Abstract
In the hydrochloride of a pyrazolyl-substituted acetylacetone, the chloride anion is hydrogen-bonded to the protonated pyrazolyl moiety. Equimolar co-crystallization with tetrafluorodiiodobenzene (TFDIB) leads to a supramolecular aggregate in which TFDIB is situated on a crystallographic center of inversion. The iodine atom in the asymmetric unit acts as halogen bond donor, and the chloride acceptor approaches the -hole of this TFDIB iodine subtending an almost linear halogen bond, with Cl···I = Å and Cl···I–C = 179.32(6)°. This contact is roughly orthogonal to the N–H···Cl hydrogen bond. An analysis of the electron density according to Bader’s Quantum Theory of Atoms in Molecules confirms bond critical points (bcps) for both short contacts, with = 0.129 for the halogen and e for the hydrogen bond. Our halogen-bonded adduct represents the prototype for a future class of co-crystals with tunable electron density distribution about the -hole contact.
Highlights
Molecules 2021, 26, 3982. https://. Starting with his first publications in the 1920s, Linus Pauling took a never-ceasing interest in both theoretical [1,2] and experimental [3,4] insights in chemical bonds. This fascination is reflected by his famous textbook The Nature of the Chemical Bond [5] and peaked in him being awarded the Nobel prize in chemistry in 1954 “for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances” [6]
A halogen’s ability to form favourable interactions with nucleophiles is called a halogen bond [7]. They form between an electron donating and an electron accepting site; in the case of halogen bonds the halogen is the electron accepting partner (Figure 1) [7,8]
We have recently shown that pyrazolyl substituted acetylacetones are heterobifunctional molecules suitable for the construction of well-ordered bimetallic coordination polymers [27]
Summary
Starting with his first publications in the 1920s, Linus Pauling took a never-ceasing interest in both theoretical [1,2] and experimental [3,4] insights in chemical bonds. This fascination is reflected by his famous textbook The Nature of the Chemical Bond [5] and peaked in him being awarded the Nobel prize in chemistry in 1954 “for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances” [6]. They form between an electron donating and an electron accepting site; in the case of halogen bonds the halogen is the electron accepting partner (Figure 1) [7,8]
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