Synthesis, crystal structure and properties of a pyrimidine modulated tripyridyldiamino ligand and its complexes

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• 作者：Rayyat Huseyn Ismayilov^a ; Wen-Zhen Wang^b ; Gene-Hsiang Lee^c ; Shie-Ming Peng^c ; Baghir A. Suleimanov^a ; ^{Baghir.Suleymanov@socar.az}
• 关键词：Ligand design ; Copper complex ; Metal&ndash ; metal interactions ; Nickel ; Electrochemistry
• 刊名：Polyhedron
• 出版年：2017
• 出版时间：28 January 2017
• 年：2017
• 卷：122
• 期：Complete
• 页码：203-209
• 全文大小：1242 K
• 卷排序：122

文摘

A new pyrimidine-modulated ligand, N2-(pyridin-2-yl)-N6-(pyrimidin-2-yl)pyridine-2,6-diamine (H2pppmda) (1), its mononuclear copper(II) complex [Cu(H2pppmda)(CH3OH)](ClO4)2 (2) and pentanickel metal string complex [Ni5(μ5-pppmda)4Cl2] (3) have been synthesized and structurally characterized. X-ray analysis showed that the free ligand exhibits the syn–anti–syn–syn conformation and intermolecular hydrogen bonds link the ligand molecules to a 1-D network along the c axis. H2pppmda coordinates to the metal atom with all-anti mode in the copper mononuclear complex 2 and the coordination geometry of the Cu(II) ion is an elongated octahedron. The [Ni5(μ5-pppmda)4Cl2] complex involves a Ni5 linear chain unit where all the Ni–Ni–Ni angles are nearly 179° and which is terminated by the two axial ligands. The pentanuclear linear metal chain is helically wrapped by four syn–syn–syn–syn type pppmda2− ligands. There are two types of Ni–Ni distance in this complex. Terminal Ni–Ni distances bonded with the axial ligand are longer (2.3669(8) Å); the inner Ni–Ni distances are short at 2.2987(6) Å. The terminal Ni(II) ions bonded with the axial ligands are square-pyramidal (NiN4Cl) with long Ni–Nav bonds (2.096 Å), consistent with a high-spin Ni(II) configuration. The inner three Ni(II) ions have short Ni–Nav bond distances (1.902(4)–1.888(4) Å), consistent with a square planar (NiN4), diamagnetic arrangement of a low-spin Ni(II) configuration. This compound exhibits magnetic behavior similar to [Ni5(μ5-tpda)4Cl2], indicating an antiferromagnetic interaction of the two terminal high-spin Ni(II) ions. Electrochemical studies showed that the pentanickel(II) complex can undergo one reversible oxidation at +0.76 V. The introduction of an electron-withdrawing pyrimidine ring to the spacer ligand retarded the oxidation of the pentanickel metal string and stabilized the complex.