Xinghao Han,Bin Liu,Zhihong Wang,Alexander Ross Craze,Hongxia Sun,Misbha Rafiq Khan,Jing Liu,Zhongyi Liu,Jinpeng Li
Based on asymmetric lithium salts of 1-(2-pyridinylmethyl)-pyrazole-3,5-dicarboxylate (2-Li 2 pmpd) or 1-(4-pyridinylmethyl)-pyrazole-3,5-dicarboxylate (4-Li 2 pmpd), four polymers [Mn(2-pmpd)(H 2 O)] n (1), {[Mn 2 (4-pmpd)(pd)(H 2 O) 3 ]·H 2 O} n (2), [Co(4-pmpd)(H 2 O)] n (3) and [Co(2-pmpd)(H 2 O) 2 ] n (4) [pd = pyrazole-3,5-dicarboxylate] have been hydrothermally prepared and characterized structurally. 1 displays three-dimensional (3D) network with (4 4 .8 4 ) topology, 2 and 3 show 2D framework with (4 2 ·5·6 3 )(4 2 ·5 2 ·6 4 ·7 2 )(5 2 ·8) and (4 3 ) 2 (4 6 ·6 6 ·8 3 ) topologies, respectively. 4 is a 1D chain structure. Magnetization data of 1 with the 1D carboxylate bridges chain structure, fitted by the 1D model, suggests the antiferromagnetic coupling with J = −2.07 cm −1 . The carboxylate bridges in 1 adopt common syn - syn and unidentate oxygen-bridge modes. 2 with the Mn 4 unit, exhibits antiferromagnetic coupling with J = −0.68 cm −1 and z J ′ = −0.317 cm −1 . The carboxylate bridges in 2 adopt common syn - anti and the unidentate oxygen-bridge modes. In the Co 2 units, magnetization data for 3 shows the weak antiferromagnetic coupling. Variable temperature magnetic studies of 4 reveal ferromagnetic intrachain interactions and antiferromagnetic interchain magnetization interactions. The M ( H ) curves for 3 and 4 are consistent with their antiferromagnetic or ferromagnetic natures.
Two polymeric carboxylato-bridged manganese(II) complexes, \( {}_{\infty }^{1} \) [Mn(bpe)(NBA) 2 ] ( 1 ) and \( {}_{\infty }^{1} \) [Mn(bpe)(MBA) 2 ] ( 2 ) (bpe = 1,2-di(4-pyridyl)ethylene; HNBA = m-nitrobenzoic acid; HMBA = m-methyl-benzoic acid), were synthesized and characterized. Compounds 1 and 2 are isostructural. X-ray diffraction studies show that the title compounds possess a double chain structure. The chains in 1 and 2 are assembled into 2-D layers via C–H···O hydrogen bonds interactions. Furthermore, owing to the offset face-to-face π–π stacking interactions, the adjacent 2-D layers embed into each other to form a 3-D supramolecular framework. Variable-temperature (2–300 K) magnetic susceptibility measurements show the presence of weak antiferromagnetic interactions between the high-spin Mn(II) (S = 5/2) ions through a carboxylato bridge with the best fit parameters for 1 being J = −0.13 cm −1 , zJ′ = −0.098 cm −1 and for 2 , J = −0.33 cm −1 , zJ′ = −0.001 cm −1 .
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