Structural and magnetic behavior of mono- and dinuclear nickel (II) complexes of N,N 0 -bis-(3,5-dipiperidin-1-yl-[2,4,6]triazin-1-yl)- pyridin-2-ylmethyl-ethane-1,2-diamine Iraklii I. Ebralidze a , Gregory Leitus b , Linda J.W. Shimon b , Ronny Neumann a, * a Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel b Chemical Research Support Unit, Weizmann Institute of Science, Rehovot 76100, Israel article info Article history: Received 21 April 2009 Received in revised form 22 June 2009 Accepted 26 June 2009 Available online 3 July 2009 Keywords: Nickel (II) complex Schiff base Amine ligands Azido bridge Structure abstract Reaction of nickel (II) perchlorate with the ligand N,N 0 -bis-(3,5-dipiperidin-1-yl-[2,4,6]triazin-1-yl)-pyri- din-2-ylmethyl-ethane-1,2-diamine yields an octahedral Ni(II) high-spin complex 1 ([C 40 H 56 N 14 Ni (H 2 O)(CH 3 OH)](ClO 4 ) 2 (CH 3 OH) 2 ) with moderate zero-field splitting (ZFS) axial distortion parameter D/k B = 5.37 K. The ligand contributes a N4 donor set; the remaining two coordinating positions are occu- pied by coordinating solvents molecules. Exchange of the coordinating solvents molecules in complex 1 to thiocyanate moieties leads to formation of complex 2 ([C 40 H 56 N 14 Ni(NCS) 2 ](CHCl) 3 ) with an extended parameter D/k B = 8.80 K. The analysis of the structural and magnetic properties of complexes 1 and 2 led to the design of dinuclear complex 3 ([C 40 H 56 N 14 NiN 3 ] 2 (ClO 4 ) 2 (CH 3 OH) 2 ), where two azido groups were utilized as bridging ligands. The double azido bridges in complex 3 cross each other to form a rarely observed non-coplanar (N 3 ) 2 structure. The magnetic behavior of complex 3 reveals ferromagnetic cou- pling interactions characterized by J/k B = 23.25 K, D 1 /k B = 7.90 K, D 2 /k B = 0.54 K. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction In recent years, considerable attention has been paid to molecu- lar magnetism and single-molecule magnets [1]. Such compounds offer the prospect of producing magnets fabricated through con- trolled, low-temperature, solution-based chemistry, as opposed to high-temperature metallurgical routes, and also provide the possi- bility of tuning magnetic properties through synthesis [2]. These ef- forts are further motivated by the objective of having denser information-recording media that would allow data storage several orders of magnitude greater than is currently possible. However, with respect to retention of recorded information there is a compet- itive magnetic tunneling effect that leads to the degradation of information [3]. The energy barrier must be large enough to prevent the degradation of information and therefore the magnetic anisot- ropy (the absolute value of the zero-field splitting (ZFS) D-parame- ter) needs to be high [4]. From this point of view octahedral Ni(II) high-spin complexes that show moderate-to-high D-parameter val- ues [5] that can be determined using well-developed methods [6] are promising compounds for the design of molecular magnets. In this article, we present the synthesis and characterization of a series of Ni(II) complexes with the ligand N,N 0 -bis-(3,5-dipiperi- din-1-yl-[2,4,6]triazin-1-yl)-pyridin-2-ylmethyl-ethane-1,2-dia- mine, (L, Scheme 1). Recently our group has shown that substitution at the bridging nitrogen atoms in the parent N,N 0 -bis-pyridin-2-ylmethyl-ethane-1,2-diamine ligand by the 2,4-(di-piperidin-1-yl)-[1,3,5] triazine-6-yl group led to a closed- framework architecture in a copper (II) complex [7]. We hypothe- sized that the very same coordination involving both the pyridine and bridging nitrogen atoms should take place in the correspond- ing nickel (II) complexes. If so, the complex is expected to have octahedral coordination mode around Ni (II) due to steric hindr- ance of the ligand. The ligand would contribute a N4 donor set. The remaining two coordinating positions of the octahedral complex may be occupied by either coordinating solvent molecules or counter anions that can be varied. Motivated by the above considerations, mononuclear complexes 1 ([C 40 H 56 N 14 Ni(H 2 O) (CH 3 OH)](ClO 4 ) 2 (CH 3 OH) 2 ) and 2 ([C 40 H 56 N 14 Ni(NCS) 2 ](CHCl) 3 ) as well as azide bridged bimetallic complex 3 ([C 40 H 56 N 14 NiN 3 ] 2 (ClO 4 ) 2 (CH 3 OH) 2 ) were synthesized and fully characterized by IR, elemental analysis (C, H, N), magnetic measurements and single crystal X-ray diffraction analysis. 2. Results and discussion 2.1. Synthesis of the complexes The addition of a methanol solution of Ni(ClO 4 ) 2 to a chloroform solution of the ligand (L) followed by slow evaporation of the 0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2009.06.050 * Corresponding author. E-mail address: Ronny.Neumann@weizmann.ac.il (R. Neumann). Inorganica Chimica Acta 362 (2009) 4760–4766 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica