Anticooperativity of Multiple Halogen Bonds and Its Effect on Stoichiometry of Cocrystals of Perfluorinated Iodobenzenes

Abstract

To investigate influences on the topicity of perfluorinated halobenzenes as halogen bond (XB) donors in the solid state, we have conducted a database survey and prepared 18 novel cocrystals of potentially ditopic (13ditfb, 14ditfb) and tritopic (135titfb) XB donors with 15 monotopic pyridines. 135titfb shows high tendency to be mono-or ditopic, but with strong bases it can act as a tritopic XB donor. DFT calculations have shown that binding of a single acceptor molecule on one of the iodine atoms of the XB donor reduces the ESP max on the remaining iodine atoms and dramatically decreases their potential for forming further halogen bonds, which explains both the high occurrence of crystal structures where the donors do not achieve their maximal topicity and the observed differences in halogen bond lengths. Despite the fact that this effect increases with the basicity of the acceptor, when the increase of halogen bond energy due to the basicity of the acceptor compensates its decrease due to the reduction of the acidity of the donor, it enables strong bases to form cocrystals in which a potentially polytopic XB donor achieves its maximal topicity.

Halogen-Bonded Cocrystals of 1,3,5-Triiodo-2,4,6-trifluorobenzene and Structural Isomers of Benzoylpyridine

“…Depending on the position of benzoyl substituent, the pyridyl nitrogen atoms are of different basicities and exposed to different steric influences of the neighboring benzoyl group, which can lead to the formation of I···N, and consequently I···O halogen bonds of various geometries and relative strengths. On the other hand, titfb was selected as the halogen-bond donor because it has been shown that with asymmetric ditopic acceptors, it tends to act as a ditopic donor forming halogen-bonded chains …”

Halogen Bond Motifs in Cocrystals of N,N,O and N,O,O Acceptors Derived from Diketones and Containing a Morpholine or Piperazine Moiety

“…24,25 The list of studied halogen bond donors and especially halogen bond acceptors grows continuously. Cyclic nitrogen atoms are the most studied and reliable acceptor species, and this is especially the case for pyridine nitrogen atoms, 26 to the point that they are a valuable benchmark for donor evaluation 9,27,28 and studies on acceptor competitiveness. 29,30 In recent years, they have been followed by a variety of other, mostly nitrogen or oxygen atom containing species, such as methoxy, 31−33 nitro, 34−37 hydroxyl, 32,33,38 and nitrile 32,39−41 functional groups, and oxygen atoms in Noxides.…”

“…15 In this work, four novel Schiff bases (BM, BP, AM, AP; see Scheme 1) were synthesized by a condensation reaction from two diketones, benzoylacetone (B) and acetylacetone (A), and two primary amines, N-( 2 these acceptors; however, because of the geometric disposition of bonded atoms and its basicity (in comparison with the other sites, see above), this atom is not an expected acceptor site. As halogen bond donors, we selected two perfluorinated aromatic halogen bond (XB) donors, 1,4diiodotetrafluorobenzene (14tfib) as a linear ditopic donor and 1,3,5-triiodo-2,4,6-trifluorobenzene (135tfib) as a potentially tritopic donor 28 (Scheme 1).…”

“…In the last three decades, the halogen bond , has become recognized as a valuable tool in crystal engineering. − Because of its larger directionality (as compared to the hydrogen bond) , and tunability achievable by changing the donor halogen atom in otherwise structurally equivalent donor molecules, − the halogen bond found its way into a rising number of scientific studies on the synthesis and design of functional materials − as well as organic synthesis, , solution chemistry, , pharmaceutical, − and theoretical chemistry. , The list of studied halogen bond donors and especially halogen bond acceptors grows continuously. Cyclic nitrogen atoms are the most studied and reliable acceptor species, and this is especially the case for pyridine nitrogen atoms, to the point that they are a valuable benchmark for donor evaluation ,, and studies on acceptor competitiveness. , In recent years, they have been followed by a variety of other, mostly nitrogen or oxygen atom containing species, such as methoxy, − nitro, − hydroxyl, ,, and nitrile ,− functional groups, and oxygen atoms in N -oxides. , Some recent studies also showcased the promising halogen bond acceptor potential of nitrogen atoms in piperazine and nitrogen and oxygen atoms in morpholine , as well as the carbonyl oxygen atom. ,− So far, systematic studies of halogen bonding with these moieties were mainly limited to smaller building blocks. Searching the Cambridge Structural Database, one can find a small number of larger, relatively bulky building blocks that are halogen bonded via either the ...…”

The Halogen Bonding Proclivity of the sp3 Sulfur Atom as a Halogen Bond Acceptor in Cocrystals of Tetrahydro-4H-thiopyran-4-one and Its Derivatives

“…In the cocrystal with the linear donor 14tfib , tpyr molecules form 2D networks through C–H···O hydrogen bonding, and these networks are connected by I···S halogen bonding into a 3D network. On the other hand, in the cocrystal with the potentially tritopic 60 and nonlinear donor 135tfib , only halogen bonds are formed with the oxygen and sulfur atoms, leading to the formation of first, a halogen bonded chain, and then a halogen bonded layer when combined with I···I halogen bonds between donor molecules themselves. The only significant intermolecular hydrogen bonds are of C–H···F type, and they connect two adjacent halogen bonded layers.…”