The Morpholinyl Oxygen Atom as an Acceptor Site for Halogen-Bonded Cocrystallization of Organic and Metal–Organic Units

Abstract

We explore the halogen bond acceptor potential of the morpholinyl oxygen atom in the synthesis of cocrystals involving organic and metal−organic units, by using N-aminomorpholine either as a potential halogen bond acceptor or as a reagent to insert a morpholine moiety into larger organic and copper(II)-based metal−organic building blocks. Challenged against four well-known halogen bond donor molecules differing in binding geometry and composition, these three morpholinecontaining units have yielded a total of seven previously not reported cocrystals, of which six (86%) exhibited the formation of I•••O or Br•••O halogen bonds to the morpholinyl oxygen atom. The results illustrate the possibility to systematically insert and use a morpholine group as an efficient halogen bond acceptor into organic and metal−organic structures, thus enabling cocrystal formation.

Crystal engineering strategies towards halogen-bonded metal–organic multi-component solids: salts, cocrystals and salt cocrystals

“…13b). 103 Strategy 2c involves labile (weakly bound) ligands as halogen bond acceptors. The main challenge in their implementation lies in adjusting the synthetic procedure so that the metal complex does not decompose (due to loss of the ligand).…”

Bridging the Void: Halogen Bonding and Aromatic Interactions to Program Luminescence and Electronic Properties of π-Conjugated Materials in the Solid State

“…In this example, N–O–I XB in the bicomponent host arranged 2D assembly within layers, while offset stacking between arenes promoted ordered stacking across hexagonal layers and between guest chromophores. Among XBOFs, examples of optoelectronic function to date are rare, but as noncovalent design of organic coordination polymers and frameworks continues to advance with incorporation of π-conjugated materials, such as a 2020 example based on spirobifluorene, such designs may offer an attractive platform for merging the unique luminescent host–guest chemistry and electronic behavior seen in some COFs and MOFs with the potential dynamic and responsive behavior endowed by competitive interactions in noncovalent design. − …”

Halogen Bonding in N-Alkyl-3-halogenopyridinium Salts

“…To date, various Lewis bases (neutral molecules or charged species) have been employed as halogen bond acceptors in constructing halogenbonded supramolecular assemblies. These have most commonly been organic [13,14] and metal-organic [15] molecules containing electron-rich nitrogen [16][17][18][19][20][21][22][23][24][25][26] and oxygen atoms [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41], as well as inorganic anions such as halogenides [42][43][44][45][46][47][48][49][50][51][52][53][54]. The most commonly used halogen bond donors have traditionally been neutral organic molecules where a halogen atom is bonded to electron-withdrawing molecular residues.…”