THE SYNTHESIS AND STUDY OF TETRANUCLEAR CLUSTER [Fe 4 O 2 (CCl 3 COO) 8 (THF) 2 (DMF)(H 2 O)]⋅THF Denis Prodius a , Valeriu Mereacre a , Sergiu Shova b , Maria Gdaniec c , Yurii Simonov d , Lorenzo Sorace e , Andrea Caneschi e , Nicolae Stanica f , Ion Geru g , Constantin Turta* a a Institute of Chemistry of the Academy of Sciences of Moldova, MD-2028 Chisinau, Moldova b State University of Moldova, MD-2009 Chisinau, Moldova c Faculty of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780, Poznań, Poland d Institute of Applied Physics of the Academy of Sciences of Moldova, MD-2028 Chisinau, Moldova e Department of Chemistry and INSTM Research Unit, University of Florence, Florence, Italy f Institute of Physical Chemistry “Murgulescu”, Romanian Academy, Bucharest, Romania g The Metrology and Material Analysis Centre, Academy of Sciences of Moldova, Chisinau, Moldova *Corresponding author: Fax:(37322) 739954; Tel:(37322) 739755; E-mail: turtalcba@yahoo.com; cturta@cc.acad.md Abstract: The novel bis(µ 3 -oxo) tetranuclear trichloracetate cluster, [Fe 4 O 2 (CCl 3 COO) 8 (THF) 2 (DMF)(H 2 O)]⋅THF (1), has been synthesised and subsequently characterised by X-ray structure analysis, magnetic measurements and infra red (IR). The structure of cluster is “butterfly” type. The Fe···Fe separation has the value of 2.883(1) - 3.441(7) Å. The coordination number of iron (III) is 6. Magnetic studies reveal the presence of an antiferromagnetic exchange in the parallelogram skeletons of the tetranuclear species. Using the spin Hamiltonian H = -2J wb (Ŝ 1 Ŝ 2 + Ŝ 2 Ŝ 3 + Ŝ 3 Ŝ 4 + Ŝ 4 Ŝ 1 ) - 2J bb Ŝ 2 Ŝ 4v + gµ β (Ŝ 1z + Ŝ 2z +Ŝ 3z + Ŝ 4z )B, the fitting parameters J bb = - 14.3 cm -1 , J wb = - 32.1 cm -1 , g = 2.07, ρ param. impur. = 4.2 %, Θ Curie-Weiss const. = -0.5 K and R = 6.8·10 -5 were obtained. Keywords: {Fe 4 O 2 } core; Homotetranuclear carboxylate; Crystal structure; Antiferromagnetic exchange. 1. Introduction For a long time the permanent interest of the investigators to oxo- carboxylate complexes of transition metals was due to their usefulness in resolving the problems of theory of magnetism of coordination compounds [1-5] and practical problems connected with the specific catalysis [6] and biological active substances [7]. In the last few years this class of substances has become the focus of much attention by the development of the new scientific direction concerning the best way to obtain single molecule magnet (SMM) [8-10]. At the same time the oxo iron carboxylate complexes are good model compounds for the active centers of a number of metalloproteins such as: hemerythrin (Hr) [11, 12], ribonucleotide reductase (RR) [11, 12], purple acid phosphatases (PAPs) [11-14]; ferreascidin (Fasc) [15, 16], and ferritin (Fn) [17,18]. Hr, RR, PAPs contain dinuclear iron sites, Fasc – supposedly - three nuclear sites, and Fn – a large polynuclear iron oxide core. After the first publication of the synthesis and study the tetranuclear iron(III) trifluoroacetate [19-21] the large number of complexes of this series was synthesized and investigated by different methods [22-26]. In attempt to continue the previous studying and obtaining the model of the active centers of polyiron enzymes we report herein the synthesis of tetranuclear iron(III) complex with trichloracetic acid. 2. Results and discussion Up to date various polynuclear complexes with chloro containing acetic acids have been synthesized and structurally characterized [27–31]. Most of these complexes were synthesized through step concerning treatment of basic acetates of d - elements with corresponding acids in aqueous solutions. It is worth mentioning that complex 1 was prepared by the procedure concerning the extract of the barium ion in heterotrinuclear complex by sulphate anion in “water-THF-toluene” mixture. 2.1. Structure The crystal 1 has a molecular structure build from neutral tetranuclear [Fe 4 O 2 (CCl 3 COO) 8 (THF) 2 (DMF)(H 2 O)] complexes and THF solvate molecules in 1:1 ratio. The X-ray study revealed that tetranuclear entity could be described as a typical “butterfly” type structure, as depicted in figure 1. The four metal atoms are linked through two µ 3 -oxo centers and six bidentate-bridged carboxylate ligands coordinated in syn-syn fashion. Other two carboxylate anions behave as monodentate ligands being coordinated to Fe(3) and Fe(4) atoms. The Fe···Fe separation within the Fe 4 (µ 3 - O) 2 core exhibit the following values: Fe(1)-Fe(4) 3.441(7); Fe(1)-Fe(3) 3.372(6); Fe(1)-Fe(2) 2.883(5); Fe(2)-Fe(4) 3.373(7); Fe(2)-Fe(3) 3.437(6) Å (Tabl.2). In contrast to Fe(3) and Fe(4), Fe(1) and Fe(2) atoms coordinate as a monodentate ligand one DMF molecule (Fe(1)-O(19) = 2.03(2) Å) and one water molecule (Fe(2)-O(1w) = 2.02(2) Å), respectively. The coordinated water molecule O(1w) forms two H-bonds, one with the oxygen atoms of solvate THF and another with the monodentate carboxylate ligands with the distances O(1w)···O(18) 2.81(4), O(1w)H···O(18) 1.97, O(1w)···O(22) 2.74(3), O(1w)H···O(18) 1.99 (Å) and angles O(1w)HO(18) 155.1, O(1w)HO(22) 140.2 (º). The Fe 4 (µ 3 - O) 2 core is essentially non-planar. The dihedral angle between two Fe 3 (µ 3 -O) fragments is equal to 33.0(1)°. The deviation of µ 3 -oxigen atoms from the respective plane is different: 0.35(1) Å for O(1) and 0.24(2) Å for O(2). Each iron ions has an O 6 slightly distorted octahedron coordination, but their environment is different. In particular, the 77