title: Dicopper(II) Metallacyclophanes with N,N'-2,6-Pyridinebis(oxamate): Solution Study, Synthesis, Crystal Structures, and Magnetic Properties.
abstract: The complexing ability of copper(II) in solution by the ligand N,N'-2,6-pyridinebis(oxamic acid) (H4mpyba, H4L) was determined through potentiometric and UV-vis spectroscopy at 25 °C and 0.15 M NaCl. The logarithms of the equilibrium constants for its copper(II) complexes according to the eqs 2H2L + 2Cu ⇆ [Cu2(H2L)2], 2H2L + 2Cu ⇆ [Cu2(H2L) (HL)] + H, 2H2L + 2Cu ⇆ [Cu2(HL)2] + 2H, 2H2L + 2Cu ⇆ [Cu2(HL)(L)] + 3H, and 2H2L + 2Cu ⇆ [Cu2L2] + 4H were 12.02(7), 8.04(5), 1.26(6), -7.51(6), and -16.36(6), respectively. The knowledge of the solution behavior has supported the synthesis of three new compounds bearing the common building block Cu2L2(4-). Their formulas are (Me4N)4[Cu2(mpyba)2(H2O)2]·H2O (1), (Me4N)4[K2Na2Cu4(mpyba)4(H2O)6.8]·1.6H2O (2), and [Na6Cu2(mpyba)2Cl2(H2O)8]·7H2O (3) (Me4N(+) = tetramethylammonium cation). The [Cu2(mpyba)2(H2O)2](4-) tetraanionic unit, which is present in 1, has a [3,3] metallacyclophane-type motif connected by two N-Cu-N bonds. In 2, a heterotrimetallic decanuclear nanocage is formed through front-to-front assembly of two [Cu2(mpyba)2](4-) units, which also coordinate to potassium(I) and sodium(I) cations by means of carboxylate oxygens from oxamate. The structure of 3 consists of heterobimetallic layers of formula [Na6Cu2(mpyba)2Cl2(H2O)8] and crystallization water molecules, which are interlinked by hydrogen bonds leading to a supramolecular three-dimensional network. The investigation of the magnetic properties of 1-3 in the temperature range 1.9-300 K shows the occurrence of ferromagnetic interactions between the dicopper(II) metallacyclophane unit [J = +6.85 (1), +7.40 (2), and +7.90 cm(-1) (3); H = -JSCu1·SCu2, where SCu1 = SCu2 = 1/2]. Theoretical calculations on 1-3 were carried to substantiate the nature and magnitude of the involved magnetic interactions and to support the occurrence of a spin polarization mechanism accounting for them.
authors.affiliation: Universidade Federal de Goiás , Instituto de Química, Campus Samambaia, CP 131, CEP 74001-970 Goiânia, GO Brazil.
authors.forename: Tamires S
authors.initials: TS
authors.lastname: Fernandes
authors.affiliation: Universidade Federal de Goiás , Instituto de Química, Campus Samambaia, CP 131, CEP 74001-970 Goiânia, GO Brazil.
authors.forename: Ramon S
authors.initials: RS
authors.lastname: Vilela
authors.affiliation: Universidade Federal de Goiás , Instituto de Química, Campus Samambaia, CP 131, CEP 74001-970 Goiânia, GO Brazil.
authors.forename: Ana K
authors.initials: AK
authors.lastname: Valdo
authors.affiliation: Universidade Federal de Goiás , Instituto de Química, Campus Samambaia, CP 131, CEP 74001-970 Goiânia, GO Brazil.
authors.forename: Felipe T
authors.initials: FT
authors.lastname: Martins
authors.affiliation: Departament de Química Inorgànica/Instituto de Ciencia Molecular (ICMol), Facultat de Química de la Universitat de València , C/Catedrático José Beltrán 2, 46980 Paterna (València), Spain.
authors.forename: Enrique
authors.initials: E
authors.lastname: García-España
authors.affiliation: Departament de Química Inorgànica/Instituto de Ciencia Molecular (ICMol), Facultat de Química de la Universitat de València , C/Catedrático José Beltrán 2, 46980 Paterna (València), Spain.
authors.forename: Mario
authors.initials: M
authors.lastname: Inclán
authors.affiliation: Departament de Química Inorgànica/Instituto de Ciencia Molecular (ICMol), Facultat de Química de la Universitat de València , C/Catedrático José Beltrán 2, 46980 Paterna (València), Spain.|Fundació General de la Universitat de València (FGUV), Universitat de València , València, Spain.
authors.forename: Joan
authors.initials: J
authors.lastname: Cano
authors.affiliation: Departament de Química Inorgànica/Instituto de Ciencia Molecular (ICMol), Facultat de Química de la Universitat de València , C/Catedrático José Beltrán 2, 46980 Paterna (València), Spain.
authors.forename: Francesc
authors.initials: F
authors.lastname: Lloret
authors.affiliation: Departament de Química Inorgànica/Instituto de Ciencia Molecular (ICMol), Facultat de Química de la Universitat de València , C/Catedrático José Beltrán 2, 46980 Paterna (València), Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: Julve
authors.affiliation: Departamento de Química, ICEx, Universidade Federal de Minas Gerais , Minas Gerais 31270-901, Brazil.
authors.forename: Humberto O
authors.initials: HO
authors.lastname: Stumpf
authors.affiliation: Universidade Federal de Goiás , Instituto de Química, Campus Samambaia, CP 131, CEP 74001-970 Goiânia, GO Brazil.
authors.forename: Danielle
authors.initials: D
authors.lastname: Cangussu