Sometimes the Same, Sometimes Different: Understanding Self-Assembly Algorithms in Coordination Networks

The syntheses and characterizations of three new ligands containing two 4,2′:6′,4″-tpy or two 3,2′:6′,3″-tpy metal-binding domains are reported. The ligands possess different alkyloxy functionalities attached to the central phenylene spacer: n-pentyloxy in 3, 4-phenyl-n-butoxy in 4, benzyloxy in 5. Crystal growth under ambient conditions has led to the formation of {[Co(NCS)(2)(3)]·0.8C(6)H(4)Cl(2)}(n) and {[Co(NCS)(2)(4)]·1.6H(2)O·1.2C(6)H(4)Cl(2)}(n), with structures confirmed by single crystal X-ray diffraction. Both the cobalt(II) center and ligand 3 or 4 act as 4-connecting nodes and both {[Co(NCS)(2)(3)]·0.8C(6)H(4)Cl(2)}(n) and {[Co(NCS)(2)(4)]·1.6H(2)O·1.2C(6)H(4)Cl(2)}(n) possess a 3D cds net despite the fact that 3 and 4 contain two 4,2′:6′,4″-tpy and two 3,2′:6′,3″-tpy units, respectively. Taken in conjunction with previously reported data, the results indicate that the role of the alkyloxy substituent is more significant than the choice of 4,2′:6′,4″- or 3,2′:6′,3″-tpy isomer in determining the assembly of a particular 3D net. The combination of Co(NCS)(2) with 5 resulted in the formation of the discrete molecular complex [Co(NCS)(2)(MeOH)(2)(5)(2)]·2CHCl(3)·2MeOH in which 5 acts as a monodentate ligand. The pendant phenyls and both coordinated and non-coordinated 4,2′:6′,4″-tpy units are involved in efficient π-stacking interactions.