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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)](C4O4)1/2·2H2O and [{Cu(BIP)(OH2)}4(μ-C4O4)](ClO4)2·4H2O

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posted on 17.11.2001, 00:00 by Y. Akhriff, J. Server-Carrió, A. Sancho, J. García-Lozano, E. Escrivá, L. Soto
Two polynuclear copper(II)−squarate compounds of formulas [Cu(HBIP)(BIP)](C4O4)1/2·2H2O (1) and [{Cu(BIP)(OH2)}4(μ-C4O4)](ClO4)2·4H2O (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 P1̄, with a =7.947(1) Å, b =12.327(4) Å, c = 13.150(3) Å, α = 113.91(2)°, β = 99.85(2)°, γ = 90.02(2)° for compound 1 and a = 8.010(1) Å, b = 13.073(1) Å, c = 14.561(1) Å, α = 72.13(1)°, β = 80.14(1)°, γ = 84.02(1)° 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 (CuN4O 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)(OH2)}4(μ-C4O4)]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 θ (−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.