Greasy tails switch 1D-coordination [Zn2(OAc)4(4'-(4-ROC6H4)-4,2':6',4''-tpy)]n polymers to discrete [Zn2(OAc)4(4'-(4-ROC6H4)-4,2':6',4''-tpy)2] complexes

The homologous series of 4′-IJ4-ROC6H4)-4,2′:6′,4″-tpy ligands with R = Me, Et, nPr, nBu, npentyl, nhexyl,
nheptyl, noctyl, nnonyl and ndecyl (1-10, respectively) are reported, including single crystal structures of
6 and 7. Reactions of zincIJII) acetate with 1-10 have been investigated using room temperature
crystallization methods (diffusion or layering). For ligands with the shortest alkoxy substituents,
1-dimensional coordination polymers ij{Zn2(OAc)4IJL)}n] IJL = 1, 2 or 3) are formed. In each polymer, the
4′-IJ4-ROC6H4)-4,2′:6′,4″-tpy ligands bind zinc through the two outer pyridine donors. The polymer
structures are similar with the n-propyl chain adopting a folded conformation in ij{Zn2(OAc)4IJ3)}n] which
allows it to fit in the cavity occupied by methyl or ethyl groups in ij{Zn2(OAc)4IJ1)}n] and ij{Zn2(OAc)4IJ2)}n].
Reaction between 5 and ZnIJOAc)2·2H2O gives both the coordination polymer ij{2Zn2(OAc)4IJ5)·2H2O}n]
and the discrete complex ijZn2(OAc)4IJ5)2]. Although the zig-zag form of the polymer chain in
ij{2Zn2(OAc)4IJ5)·2H2O}n] mimics those in ij{Zn2(OAc)4IJL)}n] IJL = 1, 2 or 3), packing interactions differ and
the wider separation of the chains in a sheet results in the incorporation of water molecules in the
lattice. π-Stacking between pyridine rings in ij{Zn2(OAc)4IJL)}n] IJL = 1, 2 or 3) produces infinite assemblies in
contrast to isolated tetradecker π-stacks in ij{2Zn2(OAc)4IJ5)·2H2O}n]. This assembly is replicated in
ij{4Zn2(OAc)4IJ7)·3H2O}n] IJn-heptoxy substituents). In contrast, the n-hexoxy-containing coordination polymer
crystallizes with acetic acid in the lattice; ij{Zn2(OAc)4IJ6)·MeCO2H}n] consists of zig-zag polymer
chains which π-stack in a manner which is unique among the other polymers. Further lengthening of
the alkoxy chain favours the formation of ijZn2(OAc)4IJL)2] IJL = 8, 9 or 10) which are analogues of
ijZn2(OAc)4IJ5)2]. In each, the 4′-IJ4-ROC6H4)-4,2′:6′,4″-tpy ligand is monodentate. The alkoxy chains are in
extended (or close to extended) conformations and pack into planar sheets with interdigitated chains.
Pockets in the sheets are occupied by methyl groups of {Zn2IJOAc)4} units in the adjacent sheet in a balland-
socket assembly motif. The study shows that coordination polymers ij{Zn2(OAc)4IJL)}n] in which
π-stacking are the dominant interactions are favoured for small alkoxy substituents (ligands 1-3); for
ligands 8-10, discrete complexes ijZn2(OAc)4IJL)2] in which van der Waals interactions dominate are
observed. In the intermediate range IJligands 5-7), the preference between the two structure types
appears to be marginal