The crystal supramolecularity of metal phenanthroline complexes

Abstract

The 1,10-phenanthroline (phen) ligand in metal complexes commonly forms offset face-to-face (OFF) motifs, and less frequently edge-to-face (EF) motifs. An investigation of the 335 M(phen) complexes, 159 M(phen)₂ complexes, and 33 M(phen)₃ complexes in the Cambridge Structural Database has revealed that in crystals these primary OFF and EF motifs combine to form concerted motifs, and extended motifs, in a variety of ways. Stacks of phen ligands engaging OFF motifs on both faces are very common for complexes M(phen) and M(phen)₂. Even more common for M(phen)₂ are zigzag chains in which each phen ligand links to neighbours in the chain with an OFF motif. The parallel fourfold aryl embrace (P4AE, comprised of one OFF and two EF) occurs for complexes M(phen)₂ and M(phen)₃, with some variety in geometry between a single OFF at one extreme to (EF)₂ at the other. This variability in the P4AE is a consequence of the larger surface area of the phen ligand, compared with those of 2,2′-bipyridyl (bipy) ligands or phenyl groups (which also form this motif), and has been evaluated by calculations of the supramolecular attractive energies. The P4AE associate further, maximising the use of phen surfaces, to form chains of P4AE, chains of P4AE·OFF, and compact two-dimensional nets propagated by both P4AE and OFF motifs. There are examples of three-dimensional nets using these motifs. There is a notable absence of sixfold aryl embraces (6AE, comprised of concerted (EF)₆) amongst M(phen)₃ complexes, and a clear difference with M(bipy)₃ complexes where 6AEs are prevalent. Various M(phen)₂ and M(phen)₃ complexes pack in crystals to form tight hydrophobic domains, often as slabs, segregated from hydrophilic domains containing hydrogen bonding components and anions. The crystallisation and crystal packing of [Co(phen)₃][BF₄]₂·H₂O·EtOH, which exemplifies this pattern, are reported. The implications for crystal engineered enantioselection by [M(phen)₃] complexes are discussed.