Novel polynuclear architectures incorporating Co 2+ and K + ions bound by dimethylmalonate anions: Synthesis, structure, and magnetic properties Ekaterina N. Zorina a,⇑ , Natalya V. Zauzolkova a , Aleksei A. Sidorov a , Grigory G. Aleksandrov a , Anatoly S. Lermontov a , Mikhail A. Kiskin a , Artem S. Bogomyakov b , Vladimir S. Mironov c , Vladimir M. Novotortsev a , Igor L. Eremenko a a N.S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky Prosp. 31, 119991 Moscow, Russian Federation b International Tomography Center, Siberian Branch of the Russian Academy of Sciences, Institutskaya Str. 3a, 630090 Novosibirsk, Russian Federation c A.V. Schubnikov Institute of Crystallography, Russian Academy of Sciences, Leninsky Prosp. 59, 119333 Moscow, Russian Federation article info Article history: Received 31 May 2012 Received in revised form 28 September 2012 Accepted 5 October 2012 Available online 5 November 2012 Keywords: Polymeric cobalt(II) complex Dimethylmalonate ligands X-ray diffraction analysis Magnetic properties abstract The reaction of potassium dimethylmalonate (K 2 Me 2 Mal) and cobalt(II) pivalate [Co(Piv) 2 ] n under various conditions resulted in {[K 2 Co(H 2 O-jO)(l-H 2 O)(l 6 -Me 2 Mal)(l 5 -Me 2 Mal)]2H 2 O} n (1) and {[K 6 Co 36 (H 2 O-jO) 22 (l-H 2 O) 6 (l 3 -OH) 20 (l 4 -HMe 2 Mal-j 2 O,O 0 ) 2 (l 6 -Me 2 Mal-j 2 O,O 0 ) 2 (l 5 -Me 2 Mal-j 2 O,O 0 ) 8 (l 4 -Me 2 Mal-j 2 O,O 0 ) 12 (l 4 -Me 2 Mal) 6 ]58H 2 O} n (2) (where Me 2 Mal 2 is the dimethylmalonate dianion). Coordination polymers 1 and 2 were characterized by X-ray diffraction and magnetochemical studies. Analysis of the magnetic behavior indicates that 1 is characterized by an extremely high anisotropy of magnetic susceptibility and very weak spin coupling between Co II centers through malonate groups; com- pound 2 contains a highly symmetric, spherical-like Co 36 metal core that exhibits low magnetic anisotropy and antiferromagnetic interactions between Co II centers. Theoretical aspects of anisotropic magnetic properties of orbitally-degenerate Co II ions in polynuclear cobalt(II) complexes are discussed. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction It is well known that, when polynuclear carboxylate complexes are constructed from malonate anions and transition metal ions, crystallization from water or water–alcohol solutions mainly gives coordination polymers with chain, layer, or frame molecular struc- tures build of the bis-chelating dianion [M II (Mal) 2 ] 2 (M II = Co, Ni, Cu, Zn) (see, for example, [1–7]). No polymeric metal-containing malonate systems incorporating large 3d metal containing frag- ment as structural units are known to date. A promising synthetic strategy to prepare such coordination compounds is based on the ligand-deficient approach that enforces malonate anions to carry out the bridging functions. In this work, we report the preparation of two novel polymeric malonate cobalt(II) complexes with potas- sium ions, one of which contains an unusual highly symmetric, spherical-like Co 36 hexanegative anion that functions as a struc- ture-forming molecular building block. These Co II complexes are structurally and magnetically characterized. We also provide some theoretical analysis of a complicated magnetic behavior of these complexes containing orbitally-degenerate six-coordinate Co II ions with an unquenched orbital momentum. 2. Experimental 2.1. Synthesis Reagents and solvents were commercial available (Aldrich) and used without further purification. Distilled water was used for the synthesis of new compounds. Polymeric cobalt pivalate [Co(Piv) 2 ] n was synthesized according to a known procedure [8]. The K 2 Me 2 Mal salt was prepared by the neutralization of KOH with H 2 Me 2 Mal. 2.1.1. {[K 2 Co(H 2 O-jO)(l-H 2 O)(l 6 -Me 2 Mal)(l 5 -Me 2 Mal)]2H 2 O} n (1) [Co(Piv) 2 ] n (0.49 g, 1.89 mmol) was added to a solution of K 2 Me 2 - Mal (obtained from potassium hydroxide (0.42 g, 7.58 mmol) and dimethylmalonic acid (0.5 g, 3.78 mmol)) in EtOH (20 ml). The reac- tion mixture was stirred with weak heating (t = 50 °C) for 10 min to produce a thick violet precipitate. The precipitate was filtered off, washed with EtOH, and dissolved in H 2 O (30 ml). The resulting crim- son solution was kept for two weeks under air at room temperature. The resulting violet crystals are suitable for X-ray diffraction analy- sis. The yield of 1 is 0.64 g (71%). Anal. Calc. for C 10 H 20 CoK 2 O 12 : C, 25.59; H, 4.29. Found: C, 25.71; H, 4.38%. IR spectra, m/cm 1 : 3495 s, 2983 m, 2941 m, 2878 m, 2103 w, 1637 s, 1607 s, 1549 s, 1478 s, 1464 m, 1441 s, 1384 m, 1357 m, 1343 s, 1207 m, 1184 m, 0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ica.2012.10.016 ⇑ Corresponding author. Tel.: +7 495 955 4817; fax: +7 495 952 1279. E-mail addresses: kamphor@mail.ru (E.N. Zorina), bus@tomo.nsc.ru (A.S. Bogomyakov), mirsa@list.ru (V.S. Mironov). Inorganica Chimica Acta 396 (2013) 108–118 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica