Chapter 4 - Jacobs University

Chapter 4
16-Iron Metal Center Nanocluster
It is of interest to compare the structure of 2 with P 8 W 48 type analogues containing other
transition metal centers. For example, we notice that the grafting mode of the 16 Fe 3+ centers in 2
is different from that of the 20 Cu 2+ centers in [Cu 20 Cl(OH) 24 (H 2 O) 12 (P 8 W 48 O 184 )] 25- . 7a In 2 each
of the 16 equivalent Fe 3+ centers is bound to P 8 W 48 via a Fe-O(W) and a Fe-O(P) bond, resulting
in a tight anchoring of the 16-iron-hydroxo core. In the Cu 20 -POM, only 8 of the 20 Cu 2+ ions
from two covalent Cu-O(W) bonds each to the P 8 W 48 host. Hence, the eight phosphate groups of
P 8 W 48 are not involved in the binding to the cationic {Cu 20 (OH) 24 } 16+ cluster guest. In fact, 2 is
structurally most closely related to Mialane’s Cu 20 -azide derivative
[P 8 W 48 O 184 Cu 20 (N 3 ) 6 (OH) 18 ] 24- . 8 In the latter, 16 of the 20 Cu 2+ ions are bound to the inner rim of
P 8 W 48 in exactly the same fashion as the Fe 3+ centers in 2. The sites of the remaining four
unique, Jahn-Teller distorted Cu 2+ ions in Mialane’s POM remain empty in 2. However, we
believe that in principle these four sites could be filled in 2 as well, for example by Cu 2+ ions. In
other words, there is a good chance that a mixed-metal (e.g. 16-iron-4-copper) derivative of 2
can be prepared.
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