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

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-amino-morpholine 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 morpholine-containing units have yielded a total of seven previously not reported cocrystals, of which six (86%) exhibited the formation of I center dot center dot center dot O or Br center dot center dot center dot 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.