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)]·0.8C₆H₄Cl₂}n and {[Co(NCS)₂(4)]·1.6H₂O·1.2C₆H₄Cl₂}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)]·0.8C₆H₄Cl₂}n and {[Co(NCS)₂(4)]·1.6H₂O·1.2C₆H₄Cl₂}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]·2CHCl₃·2MeOH 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.
Keywords: 3,2′:6′,3″-terpyridine; 4,2′:6′,4″-terpyridine; cobalt(II) thiocyanate; metal-organic framework; tetratopic ligands.