Manipulating connecting nodes through remote alkoxy chain variation in coordination networks with 4 '-alkoxy-4,2 ':6 ',4 ''-terpyridine linkers

摘要

The effects of increasing the length of the alkoxy substituent in 4'-alkoxy-4,2':6',4 ''-terpyridines when they are combined with cadmium(II) nitrate under conditions of room temperature crystallization and in the same cadmium: ligand ( 1 : 3) ratio have been investigated. The divergent ligand 4'-n-propoxy-4,2':6',4 ''-terpyridine (2) reacts with Cd(NO3)(2).4H(2)O to give[{Cd-2(NO3)(4)(2)(3)}.3CHCl(3)](n) in which the Cd atoms act as 3-connecting nodes and assemble into a (6,3) net with each ligand 2 linking adjacent Cd atoms. One of the three independent n-propoxy groups nestles into a cleft in the next 2-dimensional sheet; this 'tail-inpocket' interaction restricts the length of the alkyl chain that can be accommodated. Replacing the n-propoxy by an n-pentoxy, n-hexoxy or n-heptoxy substituent results in a switch from a ( 6,3) to ( 4,4) net; in[{Cd-2(NO3)(4)(3)(4)}.3CHCl(3)](n) (3 = 4'-n-pentoxy-4,2':6',4 ''-terpyridine) and[{Cd-2(NO3)(4)(4)(4)}.CHCl3.MeOH](n) (4 = 4'-n-hexoxy-4,2':6',4 ''- terpyridine), each Cd atom is a 4-connecting node with trans- nitrato ligands, while in[{Cd(NO3)2(5)(2)}.2MeOH](n) (5 = 4'-n-heptoxy-4,2':6',4 ''-terpyridine) a cis-arrangement of nitrato ligands is observed. The reaction between (Cd(NO3)(2).4H(2)O and 4 was also investigated using a 1 : 1 ratio of reagents; this leads to the assembly of the 1-dimensional ladder [{Cd-2(NO3)(4)(MeOH)(4)(3)] n in which each Cd atom is a 3-connecting node. In each structure, face-to-face pi-stacking of the central pyridine rings or of pyridine/phenyl rings of ligands in adjacent sheets or chains is a primary packing interaction; the role of van der Waals interactions as the chain length increases is discussed. Powder diffraction confirmed that each coordination polymer or network characterized by single crystal X-ray crystallography was representative of the bulk sample. The solid-state emission properties of ligands 2, 3 and 4 and their coordination polymers are reported; the blue emission of the free ligands is red-shifted by up to 59 nm upon formation of the coordination networks, and quantum yields are in the range 11-22%.