Versatility of squaric acid as ligand. Crystal, molecular structures and magnetic studies of four poly- or dimetallic Cu(II) complexes

• Published in: Canadian journal of chemistry 1989-07, Vol.67 (7), p.1158-1165
• Main Authors: Bernardinelli, Gerald, Deguenon, Diane, Soules, Regis, Castan, Paule
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Inorganic compounds; Metal complexes; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v89-175

The synthesis and magnetic data of four copper(II) complexes obtained from squaric acid and bipyridyl or imidazole as ligand are described. Cu(C 4 O 4 )(imidazole) 2 *2H 2 O (compound I ) is made of chains of squarato-1,3-bridged Cu(II) ions. The compound crystallizes in the monoclinic system, space group P2 1 /n, and lattice parameters a = 7.455(2) Å, b = 8.196(2) Å, c = 11.235(2) Å and β = 100.55(2)°. R F  = 0.067 for 1076 observed reflections. [Cu 2 (bipyridyl) 2 (C 4 O 4 )(H 2 O) 4 ](C 4 O 4 H) 2 -4H 2 O (compound II) is a C 4 O 4 H − salt of a squarato-1,3 bridged centrosymmetric Cu(II) dimeric cation. The compound crystallizes in the triclinic system, space group P-1and lattice parameters a = 9.021(2) Å, b = 9.017(2) Å, c = 12.581(4) Å, α = 98.58(2)°,β = 106.81(2)°, and γ = 106.03(2)°. R F  = 0.038 for 2376 reflections. Each copper atom is pentacoordinated in a distorted square-based pyramidal and is linked by two nitrogen atoms of the bipyridyl, one oxygen atom of the squarato bridge, and one oxygen atom of a water molecule in the plane and one water molecule out of plane. [Cu 2 (bipyridyl) 2 (C 4 O 4 ) (H 2 O) 2 Br 2 ] (compound III ) is a squarato-1,3 bridged copper(II) dimer. The compound crystallizes in the monoclinic system, space group P2 1 /n, and lattice parameters a = 10.480(4) Å, b = 8.503(1) Å, c = 14.590(2) Å, and β = 99.75(2)°. R F  = 0.048 for 1423 reflections. Each copper atom is pentacoordinated in a distorted square-based pyramidal and is linked by two nitrogen atoms of the bipyridyl, one oxygen atom of the squarato bridge and one oxygen atom of a water molecule in the plane, and one bromine atom out of the plane.In complexes I , II , and III , the magnetic susceptibility data could be best described by neglecting the exchange coupling. The magnetic data of [Cu(bipyridyl)(C 4 O 4 )*-4H 2 O] n ( IV ) are best explained in terms of an alternating Heisenberg ferrornagnet. The epr spectra ratify results obtained from magnetic and crystallographic measurements. Keywords: squaric acid, 3,4-dihydroxy-3-cyclobutene-1,2-dion, copper(II) dimers, copper(II) chains, magnetic properties.