Solid-State NMR and X-ray Analysis of Structural Transformationsin O—H ... N Heterosynthons Formed by Hydrogen-Bond-MediatedMolecular Recognition

摘要

The template-mediated, hydrogen-bond-driven co-crystallization of trans-1,2-bis(4-pyridyl)ethylene (bpe)and resorcinol together with 1,2-bis(4-pyridyl)ethane (bpet) yielded two new polymorphs of 2(bpe):2(res) and 2(bpet):2(res) molecular adducts, thereby exploiting the molecular specificity of resorcinol—pyridineO—H...N recognition in the presence of multiple dipyridines. Comprehensive understanding of thesubsequent [2 + 2] photodimerization of the known polymorph of 2(bpe):2(res) complex was obtainedby applying single-crystal X-ray analysis and 13C CPMAS solid-state NMR at different levels of conversion,ranging from monomer to the dimer. In addition, removal of the resorcinol template from the 2(bpe):2(res) complex yields a distorted tetrakis(4-pyridyl)cyclobutane, revealing a rather different moleculargeometry (orthorhombic, Pccn phase). Ambiguous peak splittings and the presence of unexpectedresonances in the respective 13C CPMAS NMR spectra have been successfully explained by the jointapproach of X-ray analysis and density functional theory (DFT) chemical shift computations.