| Autor: |
Fernandes TS; Universidade Federal de Goiás , Instituto de Química, Campus Samambaia, CP 131, CEP 74001-970 Goiânia, GO Brazil., Vilela RS; Universidade Federal de Goiás , Instituto de Química, Campus Samambaia, CP 131, CEP 74001-970 Goiânia, GO Brazil., Valdo AK; Universidade Federal de Goiás , Instituto de Química, Campus Samambaia, CP 131, CEP 74001-970 Goiânia, GO Brazil., Martins FT; Universidade Federal de Goiás , Instituto de Química, Campus Samambaia, CP 131, CEP 74001-970 Goiânia, GO Brazil., García-España E; 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., Inclán M; 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., Cano J; 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., Lloret F; 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., Julve M; 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., Stumpf HO; Departamento de Química, ICEx, Universidade Federal de Minas Gerais , Minas Gerais 31270-901, Brazil., Cangussu D; Universidade Federal de Goiás , Instituto de Química, Campus Samambaia, CP 131, CEP 74001-970 Goiânia, GO Brazil. |
| Abstrakt: |
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. |
