A dinuclear manganese(III) and a rare pentanuclear manganese(III) compound with a phenol–pyrazole ligand Marta Viciano-Chumillas a,b,1 , Stefania Tanase a,2 , Ilpo Mutikainen c , Urho Turpeinen c , L. Jos de Jongh b,⇑ , Jan Reedijk a,d,⇑ a Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands b Kamerlingh Onnes Laboratory, Leiden Institute of Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands c Laboratory of Inorganic Chemistry, Department of Chemistry, University of Helsinki, P.O. Box 55 (A. I. Virtasen aukio 1), 00014 Helsinki, Finland d Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia article info Article history: Received 12 January 2012 Accepted 2 March 2012 Available online 17 March 2012 Keywords: Manganese(III) complexes Pyrazole ligands Magnetic properties Ligand design abstract Reacting Mn(ClO 4 ) 2 6H 2 O and H 2 phpzEt (H 2 phpzEt = 5(3)-(2-hydroxyphenyl)-3(5)-ethylpyrazole) in methanol in the presence of sodium hydroxide yields the compound [Mn 2 (HphpzEt) 4 (H 2 O) 2 ](ClO 4 ) 2 (1). The pentanuclear [Mn 5 (l 3 -O) 2 (HphpzEt) 3 (phpzEt) 3 (OCH 3 )(HOCH 3 ) 2 (O 2 CPh)] (2) is obtained when performing a similar reaction with Mn(O 2 CPh) 2 2H 2 O. Compound 1 consists of a symmetric dinuclear manganese(III) cationic unit, [Mn 2 (HphpzEt) 4 (H 2 O) 2 ] 2+ with two non-coordinated perchlorate anions. Compound 2 is a rare pentanuclear complex containing all the manganese ions in the oxidation state III and it also has l 3 -oxido ligands. Temperature- and field-dependent magnetization studies indicate dominant antiferromagnetic interactions between the manganese(III) ions in both compounds. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Searching for new polynuclear transition-metal complexes is a subject of continuing interest. This is especially due to their exciting magnetic properties. Manganese ions are often the primary choice when designing new magnetic materials [1]. Manganese ions have paramagnetic spin states; the oxidation state of three being of particular importance, because it possesses an easy-axis-type of magnetic anisotropy. Ligand choice is crucial for stabilizing the geometry and the oxidation state of the metal ion. Carboxylates [2], Schiff-base derivatives [3] and oximes [4] derivatives have been extensively studied. A systematic search for new ligands, however, is still limited. Although pyrazole-based ligands are known for a long time, newly designed derivatives have been used only recently [5–7]. We demonstrated previously that the 5(3)-(2-hydroxy- phenyl)-3(5)-methylpyrazole ligand (abbreviated as H 2 phpzMe) is a good candidate for stabilizing the manganese(III) ion [8]. Detailed structural and magnetic studies were reported on compounds de- rived from the ligands H 2 phpzR (R = H, Me, Et, Ph) (Scheme 1) [9–13]. In this work, we demonstrate the coordination versatility of the ligand 5(3)-(2-hydroxyphenyl)-3(5)-ethylpyrazole (H 2 phpzEt). Our aim is to understand the role of the ethyl substituent at the fifth position of the pyrazole ring in the structure packing and its impact on the magnetic properties. We expect that the ethyl group would induce a more bulky hindrance than in the case of the methyl group (H 2 phpzMe) and would allow more flexibility than in the case of the phenyl (H 2 phpzPh) at the fifth position of the pyrazole ring. Details of the synthesis, X-ray crystal structures and magnetic properties will be discussed of a dinuclear manga- nese(III) compound, [Mn 2 (HphpzEt) 4 (H 2 O) 2 ](ClO 4 ) 2 (1) and of a structurally novel pentanuclear manganese(III) compound, [Mn 5 (l 3 -O) 2 (HphpzEt) 3 (phpzEt) 3 (OCH 3 )(HOCH 3 ) 2 (O 2 CPh)] (2). 2. Experimental 2.1. General remarks Starting materials were purchased from Aldrich. All manipulations were performed using materials as received. Mn(O 2 CPh) 2 2H 2 O [14], and the ligand 3(5)-(2-hydroxyphenyl)- 5(3)-ethylpyrazole (H 2 phpzEt) [15] were synthesized according to the reported procedures. Caution! Perchlorate salts are 0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2012.03.001 ⇑ Corresponding authors. Address: Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands. Tel.: +31 71 527 4459; fax: +31 71 527 4671 (J. Reedijk), tel.: +31 71 527 5466; fax: +31 71 527 5404 (L.J. de Jongh). E-mail addresses: jongh@physics.leidenuniv.nl (L.J. de Jongh), reedijk@chem. leidenuniv.nl (J. Reedijk). 1 Current address: Institut de Chimie Moléculaire et des Matériaux d’Orsay, CNRS, Université Paris-Sud, 91405 Orsay, France. 2 Current address: Van ‘t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands. Polyhedron 38 (2012) 178–184 Contents lists available at SciVerse ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly