Reversible Phase Transformation and Mechanochromic Luminescence of ZnII-Dipyridylamide-Based Coordination Frameworks

• Published in: Chemistry : a European journal 2012-04, Vol.18 (16), p.5105-5112
• Main Authors: Tzeng, Biing-Chiau, Chang, Tsung-Yi, Wei, Sheng-Luen, Sheu, Hwo-Shuenn
• Format: Article
• Language: English
• Subjects: Chemical synthesis; Chemistry; Coordination; coordination frameworks; Diffraction; Grinding; Heating; Luminescence; mechanochromism; Mechanoluminescence; Moisture; Phase transitions; polyrotaxanes; Solvents; Zinc
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201103405

A 1D double‐zigzag framework, {[Zn(paps)2(H2O)2](ClO4)2}n (1; paps=N,N′‐bis(pyridylcarbonyl)‐4,4′‐diaminodiphenyl thioether), was synthesized by the reaction of Zn(ClO4)2 with paps. However, a similar reaction, except that dry solvents were used, led to the formation of a novel 2D polyrotaxane framework, [Zn(paps)2(ClO4)2]n (2). This difference relies on the fact that water coordinates to the ZnII ion in 1, but ClO4− ion coordination is found in 2. Notably, the structures can be interconverted by heating and grinding in the presence of moisture, and such a structural transformation can also be proven experimentally by powder and single‐crystal X‐ray diffraction studies. The related N,N′‐bis‐ (pyridylcarbonyl)‐4,4′‐diaminodiphenyl ether (papo) and N,N′‐(methylenedi‐para‐phenylene)bispyridine‐4‐carboxamide (papc) ligands were reacted with ZnII ions as well. When a similar reaction was performed with dry solvents, except that papo was used instead of paps, the product mixture contained mononuclear [Zn(papo)(CH3OH)4](ClO4)2 (5) and the polyrotaxane [Zn(papo)2(ClO4)2]n (4). From the powder XRD data, grinding this mixture in the presence of moisture resulted in total conversion to the pure double‐zigzag {[Zn(papo)2(H2O)2](ClO4)2}n (3) immediately. Upon heating 3, the polyrotaxane framework of 4 was recovered. The double‐zigzag {[Zn(papc)2(H2O)2](ClO4)2}n (6) and polyrotaxane [Zn(papc)2(ClO4)2]n (7) were synthesized in a similar reaction. Although upon heating the double‐zigzag 6 undergoes structural transformation to give the polyrotaxane 7, grinding solid 7 in the presence of moisture does not lead to the formation of 6. Significantly, the bright emissions for double‐zigzag frameworks of 1 and 3 and weak ones for polyrotaxane frameworks of 2 and 4 also show interesting mechanochromic luminescence. Wet and dry: A 1D double‐zigzag framework, {[Zn(paps)2(H2O)2](ClO4)2}n (paps=N,N′‐bis(pyridylcarbonyl)‐4,4′‐diaminodiphenyl thioether), has been synthesized. A similar reaction in dry solvents led to the formation of a 2D polyrotaxane framework, [Zn(paps)2(ClO4)2]n. The structures can be interconverted by heating and grinding in the presence of moisture (see figure) and display mechanochromic luminescence.