First triangular carboxylate cluster with the Fe(II)Fe(II)Fe(II) metal core q Mikhail A. Kiskin a , Irina G. Fomina a , Grygory G. Aleksandrov a , Aleksei A. Sidorov a , Vladimir M. Novotortsev a , Yury G. Shvedenkov b,1 , Igor L. Eremenko a, * , Ilya I. Moiseev a a N.S.Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 31 Leninsky prosp., 119991 Moscow, GSP-1, Russia b International Tomography Center, Siberian Branch, RAS 630090 Novosibirsk, Institutskaya str. 3a, Russia Received 24 February 2004; accepted 27 March 2004 Available online 6 May 2004 Abstract First iron(II) carboxylate cluster with the triangular metal core K[Fe 3 (l 3 -OH)(OOCCMe 3 ) 6 (HOOCCMe 3 ) 3 ](I) has been isolated from the reaction between FeSO 4  7H 2 O and KOOCCMe 3 in the presence of the excess of pivalic acid in MeCN. The X-ray data and magnetic study show the complex molecular unit to be constructed of the Fe(II) atoms. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Pivalate iron(II) clusters; X-ray structure; Magnetic properties Driving forces and vectors for self-assembling of transition metal polynuclear complexes are still poorly understood. In an attempt to elucidate the trajectories of iron(II) complexes with O-centerd ligands oligomeriza- tion, we synthesized and characterized highly symmet- rical pivalate iron(II) complex with the three metal atoms bounded to the oxygen atom of HO-group. As a result, central oxygen atom is four-coordinated similarly to the known pivalate complexes of Ni(II) [1] and Co(II) [2]. Our experiments showed the interaction between so- lid FeSO 4  7H 2 O and KOOCCMe 3 (reagent ratio 1:2) in the presence of excess of pivalic acid in MeCN under argon to result in the insoluble potassium sulphate and colorless solution. The concentration of the solution gives rise to very air sensitive white prisms of the new complex K[Fe 3 (l 3 -OH)(OOCCMe 3 ) 6 (HOOCCMe 3 ) 3 ] (I) solvated with pivalic acid and acetonitrile molecules. The X-ray study of this product showed the anion group of complex I to be a triangular pivalate iron cluster with the Fe 3 (OH) central fragment. The iron(II) atoms of the cluster (FeFe 3.625(1), 3.630(1) and 3.660(1)  A) are bonded by pairs of the pivalate ligands (Fe–O 2.118(4)–2.180(4)  A) and l 3 -OH group (Fe–O 2.100(3), 2.114(3) and 2.124(3)  A) (Fig. 1). In contrary to the known [Fe 3 O(OOCR) 6 L 3 ] þ species with the Fe(III) atoms [3–6], the Fe 3 O fragment in complex I is non-planar (the O atom protrudes from the Fe 3 plane at 0.226  A). The potassium cation interacts with the triangle iron anion via the KO(OOCR) contacts (2.748(4)–3.059(4)  A). The magnetic measure- ments (Fig. 2) show that the l eff value of complex I decreases monotonically within the whole temperature range from 8.499 l B (300 K) up to 5.839 l B (2 K) probably due to the spin-orbital and antiferromagnetic exchange interactions. The l eff value 8.499 l B (calculated for full molecule) for I at 300 K is very close to the calculated pure spin value (8.48 l B ) for the molecule with the three Fe(II) atoms [8]. q Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2004.03.024. * Corresponding author. Tel.: +7-095-955-48-35; fax: +7-095-952- 1279. E-mail addresses: schved@tomo.nsc.ru (Y.G. Shvedenkov), ilerem@ igic.ras.ru (I.L. Eremenko). 1 Fax: +7-3832-33-1399. 1387-7003/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2004.03.024 www.elsevier.com/locate/inoche Inorganic Chemistry Communications 7 (2004) 734–736