Monohalogenated carbamates where hydrogen bonding rules without halogen bonding: Is there a link between poor carbamate crystal growth and Z'>1?

Three series of monohalophenyl-N-pyridinylcarbamate isomer grids (CxxX) are reported (with x = para-, meta-, ortho; X = fluorine, chlorine, bromine), and Cx as the aminopyridinyl group (C5NH4NH-) and xX as -CO2C6H4X. Nine crystal structures are presented with all nine structures aggregating via N-HMIDLINE HORIZONTAL ELLIPSISN intermolecular interactions as their primary hydrogen bond; as chains in CmpX, CmmX and as dimers in the CopX triad. Halogen bonding is absent and there is a preference for N-HMIDLINE HORIZONTAL ELLIPSISN and C-H/pi MIDLINE HORIZONTAL ELLIPSIS pi stacking intermolecular interactions. Structural similarities abound with all three CmpX structures isomorphous in space group Pc and with CopF and CopCl isomorphous in P1 (No. 2). Differences between the monohalogenated CxxX carbamates and their CxxM and CxxOMe relatives (M, OMe = methyl, methoxy) are discussed, especially the reluctance of CxxX to form quality single crystals as most crystallise as filamentous-like fibres under a range of crystallisation conditions. Conformational analyses of the three [3 x 3] CxxX isomer grids of minimized structures in gas-phase are detailed for comparisons with the solid-state structures. Modelling results reveal inherent steric problems in CxoX associated with bulky pendant ortho-groups (i.e. bromine). Physicochemical analyses including melting point analysis and solid-state correlations are rationalised. A question is posed as to why the CxxX carbamates are reluctant to crystallise as quality single crystals and with a higher incidence of Z ' > 1 in comparison with related carboxamides.