4,2':6',4''- and 3,2':6',3''-terpyridines: the conflict between well-defined vectorial properties and serendipity in the assembly of 1D-, 2D- and 3D-architectures

A comparative investigation of the coordination assemblies formed between Co(NCS) 2 and two monotopic 4,2':6',4''-terpyridine (4,2':6',4''-tpy) ligands or two related ditopic ligands is reported. Crystals were grown by layering MeOH solutions of Co(NCS) 2 over a CHCl 3 or 1,2-C 6 H 4 Cl 2 solution of the respective ligand at room temperature. With 4'-(2-methylpyrimidin-5-yl)-4,2':6',4''-terpyridine ( 6 ), the 1D-coordination polymer {[Co 2 (NCS) 4 (MeOH) 4 ( 6 ) 2 ]∙2MeOH∙8H 2 O} n assembles with 6 coordinating only through the outer N-donors of the 4,2':6',4''-tpy unit; coordination by the MeOH solvent blocks two cobalt coordination sites preventing propagation in a higher-dimensional network. A combination of Co(NCS) 2 and 1-(4,2':6',4''-terpyridin-4'-yl)ferrocene ( 7 ) leads to {[Co(NCS) 2 ( 7 ) 2 ]∙4CHCl 3 } n which contains a (4,4) net; the 2D-sheets associate through π-stacking interactions between ferrocenyl and pyridyl units. A 3D-framework is achieved through use of the ditopic ligand 1,4-bis( n propoxy)-2,5-bis(4,2':6',4''-terpyridin-4'-yl)benzene ( 8 ) which acts as a 4-connecting node in {[Co(NCS) 2 ( 8 ) 2 ] . 2C 6 H 4 Cl 2 } n ; the combination of metal and ligand planar 4-connecting nodes results in a {6 5 .8} cds net. For a comparison with the coordinating abilities of the previously reported 1,4-bis( n octoxy)-2,5-bis(4,2':6',4''-terpyridin-4'-yl)benzene ( 3 ), a more flexible analogue 9 was prepared. {[Co(NCS) 2 ( 9 )]∙2CHCl 3 } n contains a (4,4) net defined by both metal and ligand planar 4-connecting nodes. The n octoxy tails of 9 protrude from each side of the (4,4) net and thread through adjacent sheets; the arene-attached n octoxy chains associate through a combination of van der Waals and C-H...π interactions