The aryl chlorine-halide ion synthon and its role in the control of the crystal structures of tetrahalocuprate(II) ions

The role of the arylchlorine-halide (C-Cl center dot center dot center dot X-) synthons in the development of crystal structures of the type (nCP)(2)CuX4 center dot mH(2)O (nCP(+) = n-chloropyridinium; n = 2, 3, and 4; X = Cl- and Br-; m = 0 except for (3CP)(2)CuBr4 center dot H2O] are investigated. On the basis of detailed analysis of the synthonic interactions in these systems, it is concluded that the C-Cl center dot center dot center dot Cl- synthon plays a more significant role as a crystal engineering tool in these structures than the C-Cl center dot center dot center dot Br- synthon. In addition, it is shown that the C-Cl center dot center dot center dot X- interactions are weaker than the C-Br center dot center dot center dot X- synthons in the analogous (nBP)(2)CuX4 salts (nBP(+) = n-bromopyridinium). For all of the (nCP)(2)CuCl4 salts, the nCP(+) cations are involved in nearly linear C-Cl center dot center dot center dot Cl- interactions with Cl center dot center dot center dot Cl- distances less or equal to the sum of the van der Waals radii. Supramolecular chain networks, based on the C-Cl center dot center dot center dot Cl- and N-H center dot center dot center dot Cl- synthons, are formed with all three nCP(+) cations. In addition, a polymorph of the 4CP(+) salt contains two-dimensional networks based on these synthons. In contrast, the role of the linear C-Cl center dot center dot center dot Br- synthons is less well-defined. A supramolecular structure developed on the basis of the C-Cl center dot center dot center dot Br- and N-H center dot center dot center dot Br- synthons is observed only for (4CP)(2)CuBr4. In (2CP)(2)CuBr4 and (3CP)(2)CuBr4 center dot H2O, formation of dimeric species occurs through a combination of hydrogen and halogen bonding. The role of a previously undescribed synthon, the N(pi)center dot center dot center dot X- synthon, where the N-X vector lies roughly normal to the plane of the pyridinium ring, is explored in the further development of the three-dimensional structures.