Abstract
A single-crystal X-ray diffraction structure of a 1:1 cocrystal of two fungicides, namely dithianon (DI) and pyrimethanil (PM), is reported [systematic name: 5,10-dioxo-5H,10H-naphtho[2,3-b][1,4]dithiine-2,3-dicarbonitrile-4,6-dimethyl-N-phenylpyrimidin-2-amine (1/1), C14H4N2O2S2·C12H13N2]. Following an NMR crystallography approach, experimental solid-state magic angle spinning (MAS) NMR spectra are presented together with GIPAW (gauge-including projector augmented wave) calculations of NMR chemical shieldings. Specifically, experimental 1H and 13C chemical shifts are determined from two-dimensional 1H-13C MAS NMR correlation spectra recorded with short and longer contact times so as to probe one-bond C-H connectivities and longer-range C...H proximities, whereas H...H proximities are identified in a 1H double-quantum (DQ) MAS NMR spectrum. The performing of separate GIPAW calculations for the full periodic crystal structure and for isolated molecules allows the determination of the change in chemical shift upon going from an isolated molecule to the full crystal structure. For the 1H NMR chemical shifts, changes of 3.6 and 2.0 ppm correspond to intermolecular N-H...O and C-H...O hydrogen bonding, while changes of -2.7 and -1.5 ppm are due to ring current effects associated with C-H...π interactions. Even though there is a close intermolecular S...O distance of 3.10 Å, it is of note that the molecule-to-crystal chemical shifts for the involved sulfur or oxygen nuclei are small.
Highlights
With an increasing global population, limited availability of arable land, an increase in extreme weather events and growing pest resistance to certain existing agrochemical products, innovation in the agrochemical industry is as important as ever if we are to provide enough food for everyone
We present here an NMR crystallography analysis of the 1:1 cocrystal of two fungicides, namely dithianon (DI) and pyrimethanil (PM)
Building upon studies of pharmaceutical cocrystals by such an NMR crystallography investigation (Tatton et al, 2013; Dudenko et al, 2013; Stevens et al, 2014; Kerr et al, 2015; Sardo et al, 2015; Luedeker et al, 2016), we present here the application of this approach to an agrochemical cocrystal
Summary
With an increasing global population, limited availability of arable land, an increase in extreme weather events and growing pest resistance to certain existing agrochemical products, innovation in the agrochemical industry is as important as ever if we are to provide enough food for everyone. Ease of use and more favourable toxicology profiles being important objectives, the search for and structure-based design of potential agrochemical products needs to become more efficient (Lamberth et al, 2013). One possibility in this regard is the usage of cocrystals formed between an active ingredient and coformers or other active ingredients via reversible noncovalent interactions. We present here an NMR crystallography analysis of the 1:1 cocrystal of two fungicides, namely dithianon (DI) and pyrimethanil (PM). After a couple of hours, the powdery product had changed to a dark-olive-green colour
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