| Summary: | <p>The reaction of mixtures of Fe(O<small><sub>2</sub></small>CMe)<small><sub>2</sub></small>·2H<small><sub>2</sub></small>O and Ni(O<small><sub>2</sub></small>CMe)<small><sub>2</sub></small>·4H<small><sub>2</sub></small>O of various compositions with di-2-pyridyl ketone (py<small><sub>2</sub></small>CO, dpk) in MeCN under an inert atmosphere afforded a family of hetero-metallic enneanuclear clusters with general formula [Fe<small><sub>9−<em>x</em></sub></small>Ni<small><sub><em>x</em></sub></small>(μ<small><sub>4</sub></small>-OH)<small><sub>2</sub></small>(O<small><sub>2</sub></small>CMe)<small><sub>8</sub></small>(py<small><sub>2</sub></small>CO<small><sub>2</sub></small>)<small><sub>4</sub></small>] (<strong>2</strong>, <em>x</em> = 1.00; <strong>3</strong>: <em>x</em> = 6.02; <strong>4</strong>, <em>x</em> = 7.46; <strong>5</strong>, <em>x</em> = 7.81). Clusters <strong>2–5</strong> are isomorphous to the homo-metallic [Fe<small><sub>9</sub></small>] cluster (<strong>1</strong>) previously reported by some of us, and also isostructural to the known homo-metallic [Ni<small><sub>9</sub></small>] cluster. All four clusters contain a central M<small><sup>II</sup></small> ion in an unusual 8-coordinate site and eight peripheral M<small><sup>II</sup></small> ions in distorted octahedral environments. The distribution of Fe<small><sup>II</sup></small> and Ni<small><sup>II</sup></small> ions over these two distinct coordination sites in <strong>2–5</strong> can be established through a combination of X-ray fluorescence and Mössbauer spectroscopies, which show that Fe<small><sup>II</sup></small> preferentially occupies the unique 8-coordinate metal site while Ni<small><sup>II</sup></small> accumulates in the octahedral holes. Density functional theory indicates that the distribution of ions across the two sites arises not from any intrinsic preference of the Fe<small><sup>II</sup></small> ions for the 8-coordinate sites, but rather because of the large ligand field stabilization energy available to Ni<small><sup>II</sup></small> in octahedral coordination.</p>
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