Divalent manganese, cobalt and nickel chloride complexes with neutral N₂- and N₃-based ligands derived from 2-pyridinecarbaldehyde: Synthesis, structural features and spectroscopic studies

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• 作者：Elena A. Buvaylo^a ; Andrii K. Melnyk^b ; Vladimir V. Trachevsky^c ; Olga Yu. Vassilyeva^a ; ^{vassilyeva@univ.kiev.ua" class="auth_mail" title="E-mail the corresponding author} ; Brian W. Skelton^d
• 关键词：2-Pyridinecarbaldehyde ; Schiff base ligand ; Mn(II) ; Co(II) and Ni(II) metal complexes ; X-band EPR ; Co(II) low-spin and high-spin complexes
• 刊名：Polyhedron
• 出版年：2016
• 出版时间：17 February 2016
• 年：2016
• 卷：105
• 期：Complete
• 页码：238-245
• 全文大小：1332 K

文摘

A series of dihalide M(II) mononuclear complexes in a cis configuration, Mn(HL1)₂Cl₂·CH₃OH·H₂O (1), Co(HL1)₂Cl₂·CH₃OH·H₂O (2), Ni(HL1)₂Cl₂·2H₂O (3) and CoL2Cl₂·0.5dmf (4) (HL1 – Schiff base ligand 4-N-(2′-pyridylimine)benzoic acid; L2 – pyridin-2-yl(3-(pyridin-2-yl)imidazo[1,5-a]pyridin-1-yl) methanone, both formed in situ from 2-pyridinecarbaldehyde), have been obtained as single crystals and characterized by elemental analysis, IR and EPR spectroscopy, and single-crystal X-ray diffraction techniques. The neutral M(L1)₂Cl₂ and CoL2Cl₂ molecules in 1–3 and 4, respectively, show no crystallographically imposed symmetry with the metal atoms in a MN₄Cl₂ distorted octahedral (1–3) and CoN₃Cl₂ (4) elongated trigonal–bipyramidal geometries. In the crystal lattice molecules of 1–3 are arranged in columns propagating along the c axis; the structure of 4 can be described as layers of CoL2Cl₂ and dmf molecules alternating along the a axis. The minimum M⋯M separations in a column (1–3) and inside a layer (4) are above 8 Å. The X-band solid-state EPR spectra of 1 at room temperature and 77 K exhibit broad fine structure signals at 1600 and 3000 G (g_eff ∼ 4.14 and 2.22, respectively) resulting from ZFS of the spin states for the high-spin d⁵ metal ion. The solid-state EPR spectra of 2 are temperature dependent showing a wide unresolved line at g_eff ∼ 2.09 at room temperature and a very broad signal (ΔH_pp = 2500 G) at g_eff ∼ 4.21 at 77 K. The Ni analogue 3 is EPR-silent. The EPR spectra of 4 at both temperatures show a broad asymmetrical signal centred at g ∼ 2 suggesting the low-spin configuration; the line width is nearly independent of temperature.