Dicopper(II) Metallacyclophanes with N,N‿2,6-Pyridinebis(oxamate): Solution Study, Synthesis, Crystal Structures, and Magnetic Properties

详细信息    查看全文

• 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) (H<sub>4sub>mpyba, H<sub>4sub>L) 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 2H<sub>2sub>L + 2Cu ⇆ [Cu<sub>2sub>(H<sub>2sub>L)<sub>2sub>], 2H<sub>2sub>L + 2Cu ⇆ [Cu<sub>2sub>(H<sub>2sub>L) (HL)] + H, 2H<sub>2sub>L + 2Cu ⇆ [Cu<sub>2sub>(HL)<sub>2sub>] + 2H, 2H<sub>2sub>L + 2Cu ⇆ [Cu<sub>2sub>(HL)(L)] + 3H, and 2H<sub>2sub>L + 2Cu ⇆ [Cu<sub>2sub>L<sub>2sub>] + 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 Cu<sub>2sub>L<sub>2sub><sup>4–sup>. Their formulas are (Me<sub>4sub>N)<sub>4sub>[Cu<sub>2sub>(mpyba)<sub>2sub>(H<sub>2sub>O)<sub>2sub>]·H<sub>2sub>O (1), (Me<sub>4sub>N)<sub>4sub>[K<sub>2sub>Na<sub>2sub>Cu<sub>4sub>(mpyba)<sub>4sub>(H<sub>2sub>O)<sub>6.8sub>]·1.6H<sub>2sub>O (2), and [Na<sub>6sub>Cu<sub>2sub>(mpyba)<sub>2sub>Cl<sub>2sub>(H<sub>2sub>O)<sub>8sub>]·7H<sub>2sub>O (3) (Me<sub>4sub>N<sup>+sup> = tetramethylammonium cation). The [Cu<sub>2sub>(mpyba)<sub>2sub>(H<sub>2sub>O)<sub>2sub>]<sup>4–sup> 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 [Cu<sub>2sub>(mpyba)<sub>2sub>]<sup>4–sup> 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 [Na<sub>6sub>Cu<sub>2sub>(mpyba)<sub>2sub>Cl<sub>2sub>(H<sub>2sub>O)<sub>8sub>] 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<sup>–1sup> (3); H = −JS<sub>Cu1sub>·S<sub>Cu2sub>, where S<sub>Cu1sub> = S<sub>Cu2sub> = 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.