Effect of ethylenediamine on the formation of macro, micro, and nanostructures based on [WVI(Cat)2O2]2−

Abstract

We synthesized yellow needle-shaped crystals of (NH₃CH₂CH₂NH₃)_0.5(NH₃CH₂CH₂NH₂)[(Cat)₂W^VI(O)₂]·(NH₂CH₂CH₂NH₂), 1, with a one-dimensional chain-like quantum motif, and red bulk crystals of (NH₃CH₂CH₂NH₂)₂[(Cat)₂W^VI(O)₂], 2, with a multi-tubular quantum unit, by a slight change in the degree of protonation of ethylenediamine. By grinding and ultra-sonication, crystal 1 disintegrated into nanowires with diameters of about 18 nm and lengths of 300–1000 nm, and crystal 2 disassembled into nano-tubules with diameters of 15–18 nm and lengths of 450–550 nm. We found that the quantum motifs of the crystal lattices are a template of the nanostructures i.e. quantum-chains induced the formation of nanowires and quantum-tubules led to the production of nano-tubules. To investigate the mechanism by which such a delicate change of ethylenediamine can cause such a great transformation in the nanostructure, nano-pipe-bundles (rather than nanowires) prepared from crystal 3 were used as a comparison. Although crystals 3 and 1 have similar crystal parameters, they contain different ethylenediamine moieties i.e.3 is (NH₃CH₂CH₂NH₂)₂[(Cat)₂W^VI(O)₂]·(NH₂CH₂CH₂NH₂). As is well known, the electrostatic attraction of the doubly-protonated cation (NH₃CH₂CH₂NH₃)²⁺ to the anion [(Cat)₂W^VI(O)₂]²⁻ is stronger than that of the neutral molecule NH₂CH₂CH₂NH₂. The [(Cat)₂W^VI(O)₂]²⁻-based chains were induced to split in various manners by different protonated ethylenediamines, thereby manufacturing different nano-architectures. This paper reveals that slight changes in the protonation of ethylenediamine can induce nanostructures assembled from [(Cat)₂W^VI(O)₂]²⁻ to form a variety of morphologies and sizes. We have proposed a new idea and method to prepare quite different tungsten organic hybrid nanostructures by changing the degree of protonation of ethylenediamine.