Two polymeric compounds built from mononuclear and tetrameric squarate-copper(II) complexes by deprotonation of 3,3-bis(2-imidazolyl)propionic acid (HBIP). Synthesis, crystal structure, and magnetic characterization of [Cu(HBIP)(BIP)](C(4)O(4))(1/2).2H(2)O and [[Cu(BIP)(OH(2))](4)(mu-C(4)O(4))](ClO(4))(2).4H(2)O.

Abstract

Two polynuclear copper(II)-squarate compounds of formulas [Cu(HBIP)(BIP)](C(4)O(4))(1/2).2H(2)O (1) and [[Cu(BIP)(OH(2))](4)(mu-C(4)O(4))](ClO(4))(2).4H(2)O (2) (HBIP = 3,3-bis(2-imidazolyl)propionic acid) have been synthesized and characterized by single-crystal X-ray diffraction. Both compounds crystallize in the triclinic system, space group P1, with a =7.947(1) A, b =12.327(4) A, c = 13.150(3) A, alpha = 113.91(2) degrees, beta = 99.85(2) degrees, gamma = 90.02(2) degrees for compound 1 and a = 8.010(1) A, b = 13.073(1) A, c = 14.561(1) A, alpha = 72.13(1) degrees, beta = 80.14(1) degrees, gamma = 84.02(1) degrees for compound 2. The structure of compound 1 can be viewed as made up of [Cu(HBIP)(BIP)] units linked together by the BIP carboxylate groups to form a one-dimensional chain structure along the a axis in the crystal. The copper ion is five-coordinated (CuN(4)O chromophore) with BIP and HBIP acting as tridentate and bidentate ligands, respectively. The coordination geometry is intermediate between SP and TBP. The structure of compound 2 is made of infinite chains built from cationic tetranuclear [[Cu(BIP)(OH(2))](4)(mu-C(4)O(4))](2+) complex units, two uncoordinated perchlorate anions, and four water molecules of crystallization. The squarato group bridges the copper(II) ions, while BIP acts as a tridentate ligand, connecting through its carboxylate group the tetrameric units along the a axis. The two crystallographically independent copper(II) ions are pentacoordinated within a distorted square-based pyramid. Electronic and EPR spectra are consistent with the crystallographic data. Both compounds follow a Curie-Weiss law with very low values of theta (-0.13 and +0.12 K). In compound 2, the weak ferromagnetism interaction is discussed on the basis of the structural features and correlated with published magnetostructural data on similar squarato-bridged copper(II) compounds.