Variable Dimensionality from Mononuclear and Trinuclear to One and Two Dimensions: A Series of Copper(II) Compounds with 4,4‘-Dipyridine Dioxide

Reaction of 4,4‘-dipyridine dioxide (dpdo) and CuCl2·6H2O in aqueous solution gave an adduct [Cu(H2O)6]Cl2·2dpdo·2H2O 1, which has a hydrogen-bonded three-dimensional network. While substituting CuCl2·6H2O with
Cu(ClO4)2·6H2O, three pseudopolymorphs, namely, [Cu(dpdo)6][ClO4]2 2, [Cu3(dpdo)8(H2O)6][ClO4]6·2dpdo·6H2O 3, and [Cu(dpdo)(H2O)4][ClO4]2·2dpdo 4, were isolated. 2 consists of a mononuclear copper coordinated
with six terminal dpdo ligands. Adjacent mononuclear units are overlapped through π−π stacking of pyridine
rings to give a 2D sheet with a triangular channel. 3 forms a trinuclear cluster bridged by two dpdo molecules.
The solvate and terminal dpdo molecules are interwoven through hydrogen bonding and π−π stacking to lead to
a rectangular channel with a dimensionality of 12.98 Å × 13.44 Å. 4 has a one-dimensional chain structure
bridged by dpdo. Two solvate dpdo ligands link these chains through hydrogen bonding to generate two sets of
three-dimensional networks which are interwoven through a common conjunctive point [Cu(H2O)4]2+, yielding
a three-dimensional open framework with triangular channels. ClO4- anions are included within these channels
in 2−4 through weak C−H···O hydrogen bonding. The introduction of the second spacer, 4,4‘-bipyridine, generated
a 2D architecture [Cu(dpdo)(4,4‘-bipy)][ClO4]2·2H2O·dpdo 5, which is constructed by 4,4‘-bipy and 4,4‘-dpdo
simultaneously, exhibiting a large channel with approximate dimensionality 11.1 Å × 12.6 Å, in which solvate
4,4‘-dpdo ligand and perchlorate anions are accommodated.