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

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.

μ‐1,3‐ (trans) and μ‐1,2‐ (cis) Bonding in Squarato‐Bridged Dinuclear Copper(II) and Nickel(II) Complexes Derived from Polypyridyl Amines

“…[7,19] Polymeric structures via µ-1,2-and µ-1,3-coordination have also been reported. [11,12,22,25] More recently, the trinuclear complex, [Cu 3 (pmap) 3 (µ 1,2,3 -C 4 O 4 )](ClO 4 ) 4 · 2H 2 O {pmap = bis[2-(2-pyridyl)ethyl][(2-pyridyl)methyl]-amine} with the µ-1,2,3-coordination mode has been structurally and magnetically characterized.…”

“…The strong band observed around 1500 cm -1 is similar to that found in the spectrum of K 2 C 4 O 4 which has been tentatively assigned to a mixture of C-O and C-C stretching vibration modes. [7,26,27] In the squarato-bridged metal complexes, it has been shown that the position of the 1500 cm -1 band cannot be used as a diagnostic tool to distinguish between the coordination modes of µ 1,2 -and µ 1,3 -bis(monodentate ligand). [2,18] This was attributed to the strong influence of the blocking ligand and to the structural environment around the bridging squarato moiety.…”

Distortional Isomerism in Copper(II) Nitrato Complexes of N,N′,N″‐Tris{[(para‐nitrobenzyl)phenyl]aminoethyl}amine

“…The observed electronic reflectance spectra of the two compounds, with a maximum at around 900 nm and a shoulder around 700 nm, appeared to be significantly shifted from the solution spectrum and have characteristics more typical of trigonal-bipyramidal copper(II) complexes. [10] The solid-state EPR spectra of the two compounds consist of essentially the same isotropic or close to isotropic signals with g values around 2. The IR spectra of the two solids also show only subtle differences.…”

“…The electronic spectrum of a green solution of the complex in thf exhibited a major band at λ max = 685 nm (ε max = 270 m -1 cm -1 ) and a less intense shoulder at λ = 605 nm ( Figure 2a) consistent with the formation of a distorted trigonal-bipyramidal copper(II) complex. [10] The EPR spec- Figure 2b), which is generally found for copper(II) in a square-pyramidal geometry. [11] It should be noted, however, that similar parameters have also been reported for trigonal-bipyramidal copper(II) complexes exhibiting only small distortions towards a square-pyramidal environment, including some complexes of tripodal tren ligands.…”

A novel 1-D coordination Cu(II) polymer with alternating μ1,3-squarato and binucleating polypyridylamine bridges

“…The coordination geometry around the Cu(II) centers is a five-coordinate with a slightly distorted square pyramidal environment which is achieved by the three N-donor atoms of each arm of the ligand L, an oxygen atom of the bridging squarato moiety and by an oxygen atom of the ClO À 4 anion. The complex shows antiferromagnetic coupling between the squarato-bridged Cu(II) ions with J = À6.3 cm À1 .Ó 2009 Elsevier B.V. All rights reserved.The squarate dianion, C 4 O 2À 4 (3,4-dihydroxycyclobut-3-ene-1,2-dionate) is a very well known ligand that is capable of binding more than one metal ion at the same time leading to a variety of coordination modes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] where four types were recognized known as l-1,3-(trans) [1,3-6], l-1,2-(cis) [1,3,7-11], l-1,2,3-and l-1,2,3,4- [2,[12][13][14]. It has been pointed out that the ligand does not generally act as a bis-bidentate linker for the first raw divalent transition metal ions because of its very large bite angle relative to that observed in the oxalate dianion [15].…”