Dicopper(II) Metallacyclophanes with N,N‿2,6-Pyridinebis(oxamate): Solution Study, Synthesis, Crystal Structures, and Magnetic Properties
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- 作者：Tamires S. Fernandes ; Ramon S. Vilela ; Ana K. Valdo ; Felipe T. Martins ; Enrique García-España ; Mario Inclán ; Joan Cano ; Francesc Lloret ; Miguel Julve ; Humberto O. Stumpf ; Danielle Cangussu
- 刊名：Inorganic Chemistry
- 出版年：2016
- 出版时间：March 7, 2016
- 年：2016
- 卷：55
- 期：5
- 页码：2390-2401
- 全文大小：724K
- ISSN：1520-510X
文摘
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 Cu2L2p>4– p>. 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) (Me4Np>+ p> = tetramethylammonium cation). The [Cu2(mpyba)2(H2O)2]p>4– p> 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]p>4– p> 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 cmp>–1 p> (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.