A Z′=6 crystal structure of (E)-N,N′-dicyclohexylacetamidine

Packing Problems: High Z′ Crystal Structures and Their Relationship to Cocrystals, Inclusion Compounds, and Polymorphism

“…Similarly, the helical Z ′ = 6 structure of ( E )- N , N ′-dicyclohexylacetamidine ( 18 ) was obtained from sublimation as part of the experiments aimed at metal organic chemical vapor deposition synthesis. It is tempting to link the sublimation synthesis with the high Z ′ structure; however, the authors were unable to find any alternative lower Z ′ polymorph and concluded that the molecule exhibits packing difficulties because of its irregular and non-self-complementary molecular shape, a number of molecular conformations of similar energy, and “frustration between close packing of the cyclohexyl groups of the chains and the N–H···N intermolecular interactions.” Barbour and co-workers have explored the idea of nonsolution crystallization of a well-known inclusion-compound forming hexahost ( 19 ) and isolated a total of four polymorphs from the melt, two with Z ′ = 0.5 and two exhibiting “wasted symmetry” with Z ′ = 1. Interestingly, they concluded that one of the Z ′ = 1 polymorphs is the most stable despite it not possessing the lowest Z ′ value …”

A State of Independents: Rationalizing the High Zˈ Crystal Structures of Shikimate Esters

“…A large number of factors that influence the formation of crystal structures with high Z ˈ have been identified related to the properties of the molecule (e.g., chirality, shape, and conformational flexibility − ), the packing within the crystal (e.g., pseudosymmetry, modulation, and intermolecular interactions − ), and even the method used to produce the crystals . In the majority of cases where Z ˈ >1, these factors contribute to competition between intermolecular interactions of similar strength within the structure.…”

Heterometallic coordination framework by sodium carboxylate subunits and cobalt (III) centers obtained from a highly hydrogen bonding stabilized cobalt (II) monomeric complex

“…The study of polymorphic systems seems to be another key to understand the secrets of high Z′ structures [12]. The analysis of the electron density distribution function ρ(r) in a crystal is another approach to the study of Z′ N 1 [13][14][15]. In this paper we could study by X-ray diffraction and theoretical calculations the intermolecular hydrogen bonding interactions between the four monomers present in the asymmetric unit, Z′ = 4 of the cobalt and nickel complexes 1 and 2.…”