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Issue 4, 2012
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Magnetic and luminescent properties of Cd(ii)- and Fe(ii)-anion radical frameworks: various networks or structures influenced by metal ion sizes or in situ forming mechanisms of anion radical ligand

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Abstract

The preparation, X-ray crystallography, EPR, and magnetic and luminescent properties of three new metal–anion radical frameworks are described herein. The anion radical ligand (bipo˙) and co-ligand, 1,4-benzenedicarboxylate (BDC2), coordinate to Cd(II) centers, leading to an interpenetrated three-dimensional (3D) metal–organic frameworks (MOF), [Cd3(bipo˙)4(BDC)]n (1). Although [Fe3(bipo˙)4(BDC)]n (2) and 1 possess the same space group (tetragonal, P42/nbc), and similar rigid spirocycle-like chain and powder X-ray diffraction (PXRD) patterns, 2 exhibits an interesting spirocycle-like one-dimensional (1D) chain network, in which BDC2 behaves not as bridging co-ligand but as a counteranion, according to smaller Fe(II) ion size and long Fe1⋯Fe1′ distance between rigid chains. Thus, metal ion sizes induce different networks of isomorphous 1 and 2. Moreover, the different forming mechanisms of bipo˙ ligand also result in different structural MOFs: the in situ deprotonation of initial Hbipo˙ leads to an 1D Fe(II) MOF (2); the in situaldol condensation and then deprotonation of initial hydrochloride salt of imidazo[1,2-a]pyridin-2(3H)-one results in a two-dimensional (2D) Fe(II) MOF, [Fe3(bipo˙)22-OH)22-H2O)(BDC)]n (3). More noteworthy, in 2, BDC2 suffers large distortion, mainly attributed to its strong electrostatic interaction with the Fe(II) cation on the rigid spirocycle chain. Compounds 2 and 3 exhibit broad EPR signals, ascribed to the strong iron–anion radical antiferromagnetic coupling. 1 shows an unusual magnetic phase transition at ∼70 K, and intense fluorescence emission which can even be excited by visible light (460 nm). Both 2 and 3 show strong antiferromagnetic interaction between Fe(II) cation and radical. Compared to 1, two Fe(II) MOFs exhibit obvious blue-shift fluorescence emissions.

Graphical abstract: Magnetic and luminescent properties of Cd(ii)- and Fe(ii)-anion radical frameworks: various networks or structures influenced by metal ion sizes or in situ forming mechanisms of anion radical ligand

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Publication details

The article was received on 29 May 2011, accepted on 03 Nov 2011 and first published on 09 Dec 2011


Article type: Paper
DOI: 10.1039/C1CE05641G
CrystEngComm, 2012,14, 1439-1448

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    Magnetic and luminescent properties of Cd(II)- and Fe(II)-anion radical frameworks: various networks or structures influenced by metal ion sizes or in situ forming mechanisms of anion radical ligand

    G. Yong, Y. Li, Y. Zhang and W. She, CrystEngComm, 2012, 14, 1439
    DOI: 10.1039/C1CE05641G

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