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Keywords:

  • anion effect;
  • dipyridylamide frameworks;
  • macrocycles;
  • structural transformation;
  • X-ray diffraction

Abstract

We have synthesized a series of 1 D double-zigzag ({[Zn(paps)2(H2O)2](PF6)2}n (1), {[Zn(papo)2(H2O)2](PF6)2}n (3), and {[Zn(papc)2(H2O)2](PF6)2}n (5)) and 2 D polyrotaxane ([Zn(papc)2(PF6)2]n (6)) frameworks through the reaction of Zn(PF6)2 with dipyridylamide ligands (N,N′-bis(pyridylcarbonyl)-4,4′-diaminodiphenyl thioether (paps), N,N′-bis(pyridylcarbonyl)-4,4′-diaminodiphenyl ether (papo), and N,N′-(methylenedi-p-phenylene)bispyridine-4-carboxamide (papc), respectively), and their molecular structures have been determined through X-ray diffraction studies. From the powder X-ray diffraction (PXRD) experiments, it is found that on heating, the double-zigzag frameworks 1 and 3 undergo structural transformation to give the respective polyrotaxane frameworks 2 ([Zn(paps)2(PF6)2]n) and 4 ([Zn(papo)2(PF6)2]n), which matched well with those of their Zn(ClO4)2 analogues. Furthermore, grinding the solid samples of 2 and 4 in the presence of moisture resulted in total conversion back to the double-zigzag frameworks 1 and 3, respectively. Although the 1 D double-zigzag and 2 D polyrotaxane frameworks of ZnII-paps and -papo with ClO4 anions can be also interconverted through heating and grinding in the presence of moisture, the related ZnII-papc framework with ClO4 can only undergo a structural transformation process through heating. Surprisingly, reversible structural transformation between 5 and 6 has been proven successfully. In this work, we show that by replacing ClO4 with PF6, a series of ZnII-papx-based frameworks can be obtained. Significantly, this indicates that a remarkable anion effect on such a novel structural transformation process has been demonstrated.