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

The polydentate ligand 2,6-bis­(5-(2-hydroxyphenyl)-pyrazol-3-yl)-pyridine, H<sub>4</sub>L, 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 [Cu<sub>16</sub>L<sub>8</sub>] cluster. The sequential formation of this compound via [Cu<sub>7</sub>L<sub>8</sub>]<sup>2–</sup> intermediates, recognized in its structure, is suggested by crystallographic evidence, which shows the persistent formation of the complex salt (NBu<sub>4</sub>)<sub>2</sub>[Cu<sub>7</sub>L<sub>8</sub>] in the presence of the organic cation. Also, the crystallographic identification of the related cluster [Cu<sub>11</sub>L<sub>5</sub>(OH)<sub>2</sub>(py)<sub>12</sub>] from similar reaction conditions underscores the rich multiplicity of species attainable from this simple reaction system.