Observation of a Persistent Supramolecular Synthon Involving Carboxyl Groups and H₂O That Guides the Formation of Polycatenated Co-crystals of a Tritopic Carboxylic Acid and Bis(pyridyls)

In a nonprotic solvent, a (H₂O)₂(COOH)₃(L) supramolecular synthon was found to guide the formation of five new crystal structures together with HPB-3a (1,3,5-tris­(4-carboxyphenyl)-2,4,6-tris­(4-<i>tert</i>-butylphenyl)­benzene). This synthon acted as a 3-connected trigonal planar node (L = acetone) in <b>1</b> [(HPB-3a)­(H₂O)₂(acetone)₃] or a 4-connected trigonal pyramidal node (L = pyridyl) in <b>2</b> [(HPB-3a)­(bipy)_0.5(H₂O)₂], <b>3</b> [(HPB-3a)­(azopy)_0.5(H₂O)₂], <b>4</b> [(HPB-3a)­(bipy-ete)_0.5(H₂O)₂], and <b>5</b> [(HPB-3a)­(bipy-eta)_0.5(H₂O)₂] (bipy = 4,4′-bipyridine, azopy = azopyridine, bipy-ete = <i>trans</i>-1,2-bis­(4-pyridyl)­ethene, bipy-eta = 1,2-bis­(4-pyridyl)­ethane). The formation of this synthon could be attributed to the <i>C</i>₃-symmetry of planar HPB-3a molecules and the hydrophobic interactions between <i>tert</i>-butyl groups. <b>1</b> represents a continuously interdigitated 6³-<b>hcb</b> layer structure. <b>2</b>–<b>5</b> are with the same topology and display amazing 2D homochiral bilayers, which were penetrated in parallel by two others (“above” and “below”) with the opposite chirality to form overall 3D racemic networks. However, the synthon was not as robust in the presence of protic solvents. In <b>6</b> [(HPB-3a)­(MeOH)₃], carboxyl groups interact directly with hydroxyl groups of methanol to form 1D hydrogen bonding chains. The structure is a 3-fold interpenetrated 4⁹·6⁶-<b>acs</b> network