Structural disorder and transformation in crystal growth: direct observation of ring-opening isomerization in a metal-organic solid solution.

Ji-Jun Jiang,Guo-Bi Li,Xing-Qiang Lü,Jian-Rong He,Da-Wei Wang,Cheng-Yong Su

doi:10.1107/s2052252514015966

Abstract

A rare example is reported in which discrete Ag2 L 2 ring and (AgL)∞ chain motifs [L = N,N'-bis(3-imidazol-1-yl-propyl)-pyromellitic diimide] co-crystallize in the same crystal lattice with varying ratios and degrees of disorder. Crystal structures obtained from representative crystals reveal compatible packing arrangements of the cyclic and polymeric isomers within the crystal lattice, which enables them to co-exist within a crystalline solid solution. A feasible pathway for transformation between the isomers is suggested via facile rotation of the coordinating imidazolyl groups. This chemical system could provide a chance for direct observation of ring-opening isomerization at the crystal surface. Mass spectrometry and (1)H NMR titration show a dynamic equilibrium between cyclic and oligomeric species in solution, and a potential crystallization process is suggested involving alignment of precursors directed by aromatic stacking interactions between pyromellitic diimide units, followed by ring-opening isomerization at the interface between the solid and the solution. Both cyclic and oligomeric species can act as precursors, with interconversion between them being facile due to a low energy barrier for rotation of the imidazole rings. Thermogravimetric analysis and variable-temperature powder X-ray diffraction indicate a transition to a different crystalline phase around 120°C, which is associated with loss of solvent from the crystal lattice.

Highlights

The application of design principles that are based on the concepts of self-assembly has over the past decades produced diverse functional crystalline solids possessing important physicochemical properties (e.g. Lehn, 2002; Whitesides & Boncheva, 2002; Janiak, 2003; Mathias & Stoddart, 1992; Cook et al, 2013)
In this paper we present an interesting example where the ringopening isomerism (ROI) phenomenon is observed directly in metal–organic solid solutions, in which both discrete M2L2 rings and polymeric (ML)1 chains co-crystallize in the same crystal lattice with varying ratios and degrees of order/disorder
We have described a rare example in which Ag2L2 ring and (AgL)1 chain motifs co-crystallize in varying ratios in the same crystal, showing variable degrees of disorder depending delicately on the crystallization conditions

Summary

Introduction

The application of design principles that are based on the concepts of self-assembly has over the past decades produced diverse functional crystalline solids possessing important physicochemical properties (e.g. Lehn, 2002; Whitesides & Boncheva, 2002; Janiak, 2003; Mathias & Stoddart, 1992; Cook et al, 2013). Lehn, 2002; Whitesides & Boncheva, 2002; Janiak, 2003; Mathias & Stoddart, 1992; Cook et al, 2013) Applying these principles to coordination chemistry has offered chemists opportunities to control the chemical and structural nature of coordination assemblies and, their functionalities. Lozano et al, 2001; Brandys & Puddephatt, 2001; Qin et al, 2002; Puddephatt, 2008; Liang et al, 2009) Insight into this interdisciplinary area between the discrete and extended structures may be able to shed light on the understanding of crystal engineering, in which the growth mechanisms of the periodic crystalline solids of MOFs and CPs remain largely unknown, probably due to their typical insolubility in solvents and the difficulty in determining the degree of polymerization both in solution and in crystal growth. To look for evidence to support this hypothesis, James offered the challenge to ‘get evidence of ROP at the crystal surface’ (James, 2004)

Methods

Results

Conclusion