Crystal engineering of coordination polymers and architectures using the [Cu(2,2′-bipy)]2+ molecular corner as building block (bipy=2,2′-bipyridyl)

The [Cu(2,2'-bipy)](2+) corner unit (1) (2,2'-bipy = 2,2'-bipyridyl), made available by the metathesis of the chlorides in [Cu(2,2'-bipy)Cl-2] with poorly coordinating anions [triflate (1a), BF4- (1b) and NO3- (1c)], has been reacted with a variety of bifunctional ligands, such as 4,4'-bipyridyl (4,4'-bipy), trans-4,4'-azobis(pyridine) (azpy), 1,2-bis(4-pyridyl) ethane (bpetha), trans-1,2-bis(4-pyridyl) ethene (bpethe), 1,3-bis(4-pyridyl) propane (bpp), pyrazine (pyz), i-nicotinate (i-nic) and others. Interesting motifs have been obtained and characterized, including one-dimensional polymeric chains of different kinds, molecular rings and other architectures, depending on the ligand and the counterion. Zig-zag chains exhibiting a variated period have been observed within the species [(1)(4,4'-bipy)(CF3SO3)](CF3SO3) (2a), [(1)(azpy)(H2O)(CF3SO3)](CF3SO3) (3a), [(1)(bpethe)(BF4)](BF4) (2b), [(1)(azpy)(H2O)](NO3)(2)center dot H2O (2c) and [(1)(i-nic)(H2O)](NO3)center dot 2H(2)O (3c). Though the topology of these species is not exceptional, one of them (2c) exhibits a peculiar supramolecular organization of the chains, resulting in warp-and-woof two-dimensional sheets. With the non-rigid ligands bpp and bpetha other motifs can be obtained: the former ligand gives a festoon polymer, [(1)(bpp)(EtOH)](BF4) 2 (3b), while molecular rings are generated with the latter one in the species [(1)(bpetha)(CF3SO3)(2)](2) (4a). Pyrazine with 1a gives dinuclear species that are joined by triflate anions into ladder-like polymers in [{(1)(H2O)(CF3SO3)}(2)(pyz)](CF3SO3)(2) (5a), exhibiting in the crystal structure channels running parallel to the ladders. With the asymmetric ligand 2,4'-bipyridyl (2,4'-bipy) the monomeric species [(1)(2,4'-bipy)(H2O)(BF4)(2)] (4b) is obtained, that forms 1D chains via hydrogen bonds. A different starting species, obtained from [Cu(2,2'-bipy) Cl2] by partial metathesis of the chlorides was also employed: reaction with heptanedinitrile (hdn) gives the derivative [{(1)Cl}(2)(hdn)](BF4)(2) (5b), consisting of chains of dinuclear [(2,2'-bipy) Cu(mu-Cl)(2)Cu(2,2'-bipy)] moieties joined by the bidentate flexible ligand.