1,2,4,5-Benzenetetracarboxylate- and 2,2′-Bipyrimidine-Containing Cobalt(II) Coordination Polymers: Preparation, Crystal Structure, and Magnetic Properties

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• 作者：Oscar Fabelo ; Jorge Pas&#xe1 ; n ; Francesc Lloret ; Miguel Julve ; Catalina Ruiz-P&#xe9 ; rez
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：May 5, 2008
• 年：2008
• 卷：47
• 期：9
• 页码：3568 - 3576
• 全文大小：2399K
• 年卷期：v.47,no.9(May 5, 2008)
• ISSN：1520-510X

文摘

Three new mixed-ligand cobalt(II) complexes of formula [Co₂(H₂O)₆(bta)(bpym)]_n·4nH₂O (1), [Co₂(H₂O)₂(bta)(bpym)]_n (2), and [Co₂(H₂O)₄(bta)(bpym)]_n·2nH₂O (3) (bpym = 2,2′-bipyrimidine and H₄bta = 1,2,4,5-benzenetretracaboxylic acid) have been synthesized and characterized by single crystal X-ray diffraction. 1 is a chain compound of mer-triaquacobalt(II) units which are linked through regular alternating bis-bidentate bpym and bis-monodentate bta groups. 2 and 3 are three-dimensional compounds where aquacobalt(II) (2) and cis-diaquacobalt(II) (3) entities are linked by bis-bidentate bpym (2 and 3) and tetrakis- (2 and 3) and octakis-monodentate (2) bta ligands. The cobalt atoms in 1–3 exhibit somewhat distorted octahedral surroundings. Two bpym-nitrogen atoms (1–3) and either two bta-oxygens (2) or one bta-oxygen and a water molecule (1 and 3) build the equatorial plane, whereas the axial positions are filled either by two water molecules (1) or by a bta-oxygen atom and a water molecule (2 and 3). The values of the cobalt−cobalt separation across the bridging bpym vary in the range 5.684(2)−5.7752(7) Å, whereas those through the bta bridge cover the ranges 5.288(2)−5.7503(5) Å (across the anti-syn carboxylate) and 7.715(3)−11.387(1) Å (across the phenyl ring). The magnetic properties of 1–3 have been investigated in the temperature range 1.9–290 K. They are all typical of an overall antiferromagnetic coupling with the maxima of the magnetic susceptibility at 14.5 (1) and 11.5 K (2 and 3). Although exchange pathways through bis-bidentate bpym and carboxylate-bta in different coordination modes are involved in 1–3, their magnetic behavior is practically governed by that across the bpym bridge, the magnitude of the exchange coupling being J = −5.59(2) (1), −4.41(2) (2), and −4.49(2) (3) with the Hamiltonian Ĥ = –JŜ₁Ŝ₂.