The synthesis, molecular structure and supramolecular architecture of complexes between the ammonia adduct of tris(pentafluorophenyl)boron and a series of mono and polydentate hydrogen-bond acceptors.
The ammonia adduct of tris(pentafluorophenyl)boron, (C6F5)3B.NH3, is a potentially tri-functional hydrogen-bond donor. Co-crystallisation with the bases acetonitrile, pyridine, tetrahydrofuran, tetramethylethylenediamine, 15-crown-5, 1,4-diazabicyclo[2.2.2]octane (DABCO), pyrazine and 4,4'-bipyridine results, not in donor exchange, but in the formation of supermolecules assembled through hydrogen bonding to second coordination sphere acceptors. The complexes have been characterised by elemental analysis, multinuclear NMR and single-crystal diffraction methods. The solid-state architectures range in complexity, from the hydrogen bonded pairing of (C6F5)3B.NH3, with a single monodentate acceptor molecule (e.g. MeCN to form (C6F5)3B.NH3.NCMe), through complexation with all three N-H groups to the macrocycle 15-crown-5, to the formation of infinite one-dimensional chains with pyrazine and DABCO, and to two-dimensional networks with the divergent acceptor 4,4'-bipyridine.
Molecules embracing in crystals
We review the main types of intermolecular embrace motifs adopted by molecules with arylated surfaces, and draw attention to some recent interesting developments.
Interaction of Diclofop-Methyl and MCPA on Wild Oats (Avena fatua)
Diclofop-methyl {methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate} loses part of its activity on wild oats (Avena fatua L.) when it is applied in combination with ester or amine formulations of MCPA {[4-chloro-o-tolyl)oxy] acetic acid.} Uptake of diclofop-methyl is reduced in the presence of commercial formulations of MCPA, particularly amine formulations, which are only partly compatible with the diclofop-methyl formulation. With added MCPA, regardless of formulation, hydrolysis of diclofop-methyl to the acid diclofop is slowed down, both in intact wild oat plants and in a crude leaf extract. At the same time, conversion of any acid formed to inactive conjugates is accelerated in the presence of MCPA. It is concluded that the loss of activity of diclofop-methyl by MCPA can be accounted for by the effects of MCPA on uptake and metabolic conversion of diclofop-methyl.