Supramolecular Structures from Three New Molecular Building Blocks Based on the Protonation/Deprotonation of 3,3-Bis(2-imidazolyl)propionic Acid (HBIP):  [H₃BIP](C₄O₄)·H₂O, [Cu(HBIP)₂](HC₄O₄)₂, and [Cu(BIP)₂]·2H₂O

Abstract

This paper reports the synthesis, structure solution, and electronic and electron paramagnetic resonance (EPR) characterization of three new HBIP-containing compounds (HBIP = 3,3-bis(2-imidazolyl)propionic acid): [H3BIP](C4O4)·H2O (1), [Cu(HBIP)2](HC4O4)2 (2), and [Cu(BIP)2]·2H2O (3). The structure of 1, resulting from the cocrystallization of [H3BIP]2+ and SQ2-, is made up of squarate anions, diprotonated HBIP, and water molecules packed together by multiple-path H-bonding into a supramolecular 3D network. Compounds 2 and 3 constitute the first cases of structurally characterized Cu(II)−HBIP/BIP complexes in which the ligand acts in a tridentate chelating fashion. They consist of Jahn−Teller elongated octahedral mononuclear Cu(II) units packed together into a 3D network driven in each case by a different set of multiple H-bonding paths. These differences in the supramolecular crystal packing of 2 and 3 arise from the different nature of the uncoordinated counterparts, HSQ- in 2 vs H2O in 3, which play a critical role in the set of H-bonding interactions. The use of simple anion templation to modify the network topology is discussed. Electronic and EPR spectra are indicative of an essentially dx2-y2 ground state for the copper(II) ions in 2 and 3.