Mo- and
W‑Based Organic Nanostructures Prepared from Bulk Crystal Isomorphs
Consisted of [(CH<sub>3</sub>CH<sub>2</sub>)<sub>3</sub>NH)]<sub>2</sub>[MO<sub>2</sub>(C<sub>14</sub>H<sub>6</sub>O<sub>4</sub>)<sub>2</sub>] (M = Mo, W)
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Abstract
Two new crystal isomorphs consisting
of complexes [(CH<sub>3</sub>CH<sub>2</sub>)<sub>3</sub>NH)]<sub>2</sub>[MoO<sub>2</sub>(C<sub>14</sub>H<sub>6</sub>O<sub>4</sub>)<sub>2</sub>] (<b>1</b>) and [(CH<sub>3</sub>CH<sub>2</sub>)<sub>3</sub>NH)]<sub>2</sub>[WO<sub>2</sub>(C<sub>14</sub>H<sub>6</sub>O<sub>4</sub>)<sub>2</sub>] (<b>2</b>)
have been synthesized, respectively,
and from which Mo-based flexible and durable nanopipes with
diameters of 16 nm and lengths of hundreds of micrometers and W-based
rigid and fragile nanotubules with ununiform diameters ranging from
30 to 100 nm and lengths in tens of micrometers have been prepared
separately, which revealed that the change of the metal in the coordination
center of the isomorphs can result in obvious variation to their nanostructures.
The crystals both exhibited multilayered structures by the piling
of lamellar repeating motifs through van der Waals forces, which are
formed by the parallel alignment of 1D chains through hydrogen bonds,
and the 1D chains are assembled by complexes <b>1</b> and <b>2</b>, respectively, through geometrical intercalation and π–π
packing. However, under grinding and ultrasonication, crystal <b>1</b> disassembled uniformly into longer and narrower nanostrips,
whereas crystal <b>2</b> were broken at random into shorter
and wider nanoribbons; therefore, the two lamellar nanostructures
curled into different cylindrical nanospecies. The differences
caused by Mo and W are the following: the Mo complex prefers to assemble
into more durable one-dimensional structures along Mo–O bonds
than W isomorphs; since Mo–O bonds are weaker than MoO
and W–O bonds, then the weakest Mo–O bonds can be supported
by the adjacent molecules through intercalation and π–π
packing, which resulted in that the linkages among the Mo complexes
are stronger along the Mo–O direction and hence the longer
Mo-based cylindrical structure. Moreover, the flexibility of Mo-based
nanopipes and the rigidity of W-based nanotubules might be attributed
to that Mo possesses a lower melting point than W; therefore, Mo is
softer and W is harsher
