A ferromagnetic tetranuclear nickel(II) Schiff-base complex with an asymmetric Ni 4 O 4 cubane core q Sudeshna Saha a , Souvik Pal a , Carlos J. Gómez-García b , Juan M. Clemente-Juan b , Klaus Harms c , Hari Pada Nayek a,⇑ a Department of Applied Chemistry, Indian School of Mines, Dhanbad 826004, Jharkhand, India b Instituto de CienciaMolecular (ICMol), Universidad de Valencia, C/ Catedrático José Beltrán, 2, 46980 Paterna, Valencia, Spain c Fachbereich Chemie, Philipps Universität Marburg, Hans Meer-wein Strasse, Marburg, Germany article info Article history: Received 17 December 2013 Accepted 24 February 2014 Available online 4 March 2014 Keywords: Nickel(II) complex Schiff base ligands Ni 4 O 4 cubane Ferromagnetic interaction Solid-state structure abstract The ferromagnetic tetranuclear nickel(II) complex [Ni 4 (L) 4 (CH 3 OH) 2 ]2MeOH8H 2 O(1) has been synthe- sized by reacting nickel nitrate hexahydrate with the Schiff base ligand H 2 L (H 2 L= N-(2-hydroxyphenyl)- 3-methoxy-salicylideneamine). Complex 1 was characterized by analytical, thermogravimetric, optical and magnetic techniques. The solid state structure of 1 was established by single crystal X-ray diffraction analysis. Crystal structure determination shows the formation of a distorted Ni 4 O 4 cubane moiety encap- sulated by four Schiff base ligands. Compound 1 crystallizes in the triclinic space group P  1 with a = 12.7624(9) Å, b = 15.0477(9) Å, c = 16.8589(10) Å, a = 94.732(2)°, b = 94.308(2)°, c = 99.136(2)° and Z = 2. The magnetic properties of complex 1 show a predominant ferromagnetic coupling inside the Ni 4 cluster with g = 2.240, J 1 = +0.88 cm 1 , J 2 = +0.84 cm 1 , J 3 = 0.014 cm 1 , J 4 = +1.22 cm 1 and D = 9.6 cm 1 . Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The design and synthesis of polynuclear metal complexes have attracted tremendous attention because of their structural diver- sity and potential applications in biology, catalysis, molecular rec- ognition and magnetism [1,2]. In this context, tetranuclear cubane- like Ni 4 O 4 complexes have been a very important class of mole- cules [3]. Most of these complexes have been synthesized by using a polydendate ligand which features nitrogen and oxygen donor atoms. Four nickel centers are linked by four l 3 -oxygens arising from hydroxido, alkoxido and methoxido moities [4–7]. A variety of ligands have been used ranging from simple aldehydes and pyr- idyl-alcohols to Schiff-base ligands derived from aldehyde and amino alcohols. For instance, 3,5-dichloro-2-hydroxy-benzalde- hyde, 2-hydroxy-3-methoxy-benzaldehyde, 5-bromo-2-hydroxy- benzaldehyde and 2-hydroxy-3-ethoxy-benzaldehyde have been employed to synthesize tetranuclear nickel complexes with a Ni 4 O 4 core [8–10]. 2-Hydroxymethylpyridine, gem-diol form of di-2-pyridyl ketone, 8-quinolinol and its derivatives have also been used [11–15]. Moreover, several tetranuclear nickel complexes have been sta- bilized by several Schiff-base ligands [16–20]. In general, Ni 4 O 4 cubane is highly symmetric and may present either ferromagnetic or antiferromagnetic interactions among the nickel ions. The sym- metry of the cube can be modified with the coordinating ligands and the crystallization conditions such as solvent, temperature, guest molecules and pH. The lowering of the symmetry implies dif- ferences in the Ni–O–Ni angles that may lead to the presence of both ferro- and antiferromagnetic intra-molecular interactions. Interestingly, among the ca. 120 structures of Ni 4 O 4 cubanes deposited in the CCDC database (updated Nov 2013) there are very few examples with no symmetry elements at all as in our com- pound [21]. Recently, we have started to develop new polynuclear metal complexes based on polydendate Schiff-base ligands in order to tune the magnetic properties of the synthesized complexes. Here we present the results obtained with the Schiff-base ligand N-(2- hydroxyphenyl)-3-methoxy-salicylideneamine (H 2 L) [22] which can coordinate to one or two metal ions simultaneously (Scheme 1). Reaction of H 2 L with nickel(II) nitrate hexahydrate in presence of triethyl amine in methanol results in the formation of a tetranuclear Ni(II) complex, [Ni 4 (L) 4 (MeOH) 2 ]2MeOH8H 2 O (1) that contains a http://dx.doi.org/10.1016/j.poly.2014.02.036 0277-5387/Ó 2014 Elsevier Ltd. All rights reserved. q This paper is dedicated to Prof. Dr. Werner Massa on the occasion of his 70th birthday. ⇑ Corresponding author. Tel.: +91 326 2235756; fax: +91 326 2296563. E-mail address: hpnayek@yahoo.com (H.P. Nayek). Polyhedron 74 (2014) 1–5 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly