  Bismuth compounds are of growing interest with regard to potential
applications in catalysis, medicine and electronics, for which their
environmentally benign nature is one of the key factors. The most common
starting material is bismuth nitrate, which easily hydrolyses to give a large
number of condensation products. The so-called bismuth subnitrates are composed
of bismuth oxido clusters of varying composition and nuclearity. One reason
that hampers the further development of bismuth oxido-based materials, however
is the low solubility of the subnitrates, which makes targeted immobilisation
on substrates challenging. We present an approach towards solubilisation of
bismuth oxido clusters by introducing an amino carboxylate as functional group
and a study of the growth mode of these atom-precise nanoclusters on gold
surfaces. For this purpose the bismuth oxido cluster
[Bi38O45(NO3)20(dmso)28](NO3)4*4dmso (dmso=dimethyl sulfoxide) was reacted with
the sodium salt of tert-butyloxycabonyl(Boc)-protected phenylalanine (Phe) to
give the soluble and chiral nanocluster [Bi38O45(Boc-Phe)24(dmso)9]. The
hydrodynamic diameter of the cluster was estimated with (1.4-1.6) nm (in CH3CN)
and (2.2 nm-2.9) nm (in Ethanol) based on dynamic light scattering (DLS). The
full exchange of the nitrates by the amino carboxylates was proven by NMR and
FTIR as well as elemental analysis (EA) and XPS. The solubility of the bismuth
oxido cluster in a protic as well as an aprotic polar organic solvent and the
growth mode of the clusters on Au upon spin-, dip-, and drop-coating on gold
surfaces were studied. Successful deposition of bismuth oxido cluster was
proven by powder XRD, FTIR, and XPS while the microstructure of the resulting
films was investigated as a function of the deposition method and the solvent
used by SEM, AFM, and optical microscopy.
