Linear or Cyclic Clusters of Cu(II) with a Hierarchical Relationship

The
polydentate ligand 2,6-bis­(5-(2-hydroxyphenyl)-pyrazol-3-yl)-pyridine,
H4L, exhibits a series of coordination pockets favoring
the establishment of metal sequences with predetermined motifs, together
with a degree of flexibility for the formation of clusters with various
overall topologies. With Cu­(II) under strong basic conditions it has
a marked tendency to stabilize a cyclic [Cu16L8] cluster. The sequential formation of this compound via [Cu7L8]2– intermediates, recognized
in its structure, is suggested by crystallographic evidence, which
shows the persistent formation of the complex salt (NBu4)2[Cu7L8] in the presence of the
organic cation. Also, the crystallographic identification of the related
cluster [Cu11L5(OH)2(py)12] from similar reaction conditions underscores the rich multiplicity
of species attainable from this simple reaction system.