Chapter 4 - Jacobs University

Chapter 4
16-Iron Metal Center Nanocluster
Chapter 4
Nucleation process in the cavity of a 48-tungstophosphate
wheel resulting in a 16 metal center iron-oxide nanocluster
4.1 Introduction
Chemistry under confined geometries – and this in a general sense – has attractive aspects
which may be related to special topics of surface- 1a , geo- 1b and especially bio-sciences. 2,3 One
may ask general questions, such as: what is it like for molecules/ions to ‘house’ inside a
nanosized molecular container (or generally under constrained/shielded environmental
conditions) with respect to the interactions between them? In this context we can refer to two
scenarios: 1) such interactions take place (nearly) independent of the cavity-interior shellfunctionalities
(as in a nano-test tube) or 2) they are influenced by the shell functionalities.
Whereas in the first case, the situation allows more easily the spectroscopic
identification/characterization of the species under consideration than under bulk conditions, one
can study in the second case template directed syntheses leading to unprecedented nanospecies.
Such a process occurs in nature in different types of compartments. 3
In the case of
biomineralization we can refer to the imposition of (biological) directionality on the chemistry of
growth processes (vectorial regulation). 3 In the present study we consider templated nucleation
processes based on hydrate complexes of Fe 2+ (in presence of O 2 ) and Fe 3+ in the cavity of the
cyclic 48-tungstophosphate P 8 W 48 leading to an unprecedented 16 metal center iron-oxide
formed by linking FeO 6 octahedra. This type of nucleation is based on a breaking of symmetry
during the assembly process caused by the template effect of the cavity internal WO-groups. The
mentioned reaction of Fe 2+ in the presence of dioxygen shows an important feature: it played a
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