Abstract
Solid-state photoinitiated [2 + 2] cycloaddition reaction 2(H2bpe)(NO3)2 → (H4tpcb)(NO3)4 (bpe = 1,2-bis(pyrid-4-yl)ethylene; tpcb = 1,2,3,4-tetrakis(pyrid-4-yl)cyclobutane) was carried out in a single-crystal-to-single-crystal manner. The reaction product was characterized by means of X-ray diffraction and 1H NMR spectroscopy. Only the rctt-isomer of tpcb was found as the reaction product. Intermolecular interactions in a single crystal of (H2bpe)(NO3)2 were studied within the QTAIM approach. Although sum energy of strong and weak hydrogen bonds dominates in total packing energy, contribution of π…π stacking interactions to the packing energy is also prominent. At solid (H2bpe)(NO3)2, stacking of photoreactive H2bpe2+ cations is realized via N…C, C…C and C–H…C bonding, although no four-membered cycles formed by these bond paths was found in molecular graph representation. Reduced density gradient (RDG) surfaces and molecular Voronoi surfaces clearly demonstrate accumulation of charge density between olefin groups prone to take part in photoinitiated cycloaddition reactions. Good correlation between description of hydrogen bonding in terms of QTAIM and Voronoi approaches was demonstrated. The Voronoi approach confirmed that during the photoreaction the system of hydrogen bonds remained almost unchanged.
Highlights
Solid-state photoinitiated cycloaddition reactions are a convenient single-step path to cyclobutane derivatives [1,2,3], photosensitive functional materials [4,5] and crystalline polymers [6,7,8]
The possibility of a reaction to occur, and the structure of a reaction product depend on mutual disposition of reactive fragments that can be fixed in reactive positions with coordination bonds [9,10] and intermolecular interactions [11,12]
We succeeded to carry out the reaction in the SCSC manner, and to characterize reaction product 2 using X-ray diffraction
Summary
Solid-state photoinitiated cycloaddition reactions are a convenient single-step path to cyclobutane derivatives [1,2,3], photosensitive functional materials [4,5] and crystalline polymers [6,7,8]. One of the first documented examples of this effect was described by Schmidt [13] He demonstrated that only two of three polymorphs of cinnamic acid are photoreactive, and reaction product, a α-truxillic acid or a β-truxillic acid can be obtained from, respectively, α and β polymorphs of cinnamic acid. We publish experimental charge density distribution and analysis of intermolecular bonding in monoclinic C polymorph of (H2 bpe)(NO3 ) (1) For this compound three polymorphs were obtained to date: the triclinic [21], the monoclinic one crystallized at space group C 2/c [21,22] (denoted below as monoclinic C) and the monoclinic one crystallized at P 21 /c space group (denoted below as monoclinic P) [23]. We succeeded to carry out the reaction in the SCSC manner, and to characterize reaction product 2 using X-ray diffraction
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