Synthesis and magnetic properties of heptadecametallic Fe(III) clusters Ian A. Gass a , Constantinos J. Milios a , Marco Evangelisti b , Sarah L. Heath c , David Collison c , Simon Parsons a , Euan K. Brechin a, * a School of Chemistry, The University of Edinburgh, EH9 3JJ, UK b INFM-S National Research Center, Dipartimento di Fisica, Universita ` di Modena e Reggio Emilia, 41100 Modena, Italy c Department of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, UK Received 4 September 2006; accepted 19 September 2006 Available online 29 September 2006 Abstract Heptadecametallic, all-ferric pieces of molecular magnetite of general formula HL x [Fe 17 O 16 (OH) 12 (L) 12 Br 4 ]Br 3+x (L = b-picoline, iso- quinoline, 3,5-lutidine; x = 0, 1) are made by the simple dissolution of FeBr 3 in L. The b-picoline (or equivalent) molecules act simul- taneously as solvent, base and capping ligand. The resultant structure consists of a metal–oxygen core containing both octahedral and tetrahedral Fe(III) ions that is the exact analogue of the metal–oxygen positions seen in the magnetite lattice. Antiferromagnetic exchange between the tetrahedral and octahedral Fe(III) ions lead to the stabilization of an S = 35/2 spin ground state. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Iron; Magnetite; High spin ground states; Polymetallic clusters The current interest in the synthesis and study of poly- nuclear iron complexes stems from their importance in two fields, bioinorganic chemistry and molecular magne- tism. Attempts to model the growth of the Fe–O core pres- ent in the protein ferritin [1,2] and the processes of biomineralization [3] of, for example, magnetite, goethite and ferrihydrite, have led to an increased interest in the study of (molecular) iron oxy-hydroxides. Secondly, the discovery in the last decade or so that the magnetization of certain transition metal clusters relaxes so slowly that they can be considered zero-dimensional ‘magnets’ has led to speculation that such molecules may represent the ultimate in small size magnetic memory, and find possible application in quantum computation [4]. Iron coordination clusters constitute the second largest family of SMMs after manganese complexes [5,6], and their proliferation has benefited from the fact that many polyme- tallic Fe complexes have been made and studied for many years – for the reasons mentioned above. Successful syn- thetic strategies toward such molecules are dominated by serendipitous self-assembly, whereby various Fe(II/III) pre- cursors are mixed with a bridging ligand (or combination of bridging ligands) in a particular solvent [7]. An extremely attractive alternative synthetic strategy is to try to make molecular analogues of naturally occurring magnetic oxides. The ‘traditional’ way to achieve this is to perform ‘controlled’ hydrolysis in which a metal salt (e.g. Fe(NO 3 ) 3 Æ 9H 2 O) is dissolved in water and the pH of the solution raised by addition of base in order to form, in this case, an iron hydroxide or oxy-hydroxide core whose growth is then stopped or capped by the addition of a polyd- entate chelating ligand. Without the addition of the capping ligand, it would be expected that the hydrolysis of original hexa-aqua [Fe(H 2 O) 6 ] 3+ ion would give rise firstly to an insoluble iron hydroxide which then may transform itself into an oxy-hydroxide (e.g., goethite; a-Fe–O(OH)) phase and perhaps eventually to a thermodynamically stable oxide (e.g., haemitite; Fe 2 O 3 ). Unfortunately there exists few such examples in the literature with, perhaps, the most ‘interest- ing’ still being the prototype complex [Fe 19 O 6 (OH) 10 - (metheidi) 10 (H 2 O) 2 ] + (and its analogues) first characterized 0277-5387/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2006.09.062 * Corresponding author. E-mail address: ebrechin@staffmail.ed.ac.uk (E.K. Brechin). www.elsevier.com/locate/poly Polyhedron 26 (2007) 1835–1837