Polynuclear and Extended Coordination Compounds from Preorganized Bimetallic Components: Tuning the Magnetic Properties of Dinickel(<scp>II</scp>) Building Blocks

Abstract

Abstract Various dinucleating pyrazole ligands with chelating side arms in the 3‐ and 5‐positions of the heterocycle have been shown to form Ni II /azido complexes, where the metal ions are spanned by the pyrazolate, and an azido bridge. Four new complexes have been characterized by X‐ray crystallography and variable‐temperature magnetic susceptibility studies. The Ni ··· Ni distance, and hence the intra‐dimer coordination mode of the azide (μ‐1,1 or μ‐1,3), is determined by the chelate arm length, such that the magnetic properties of the bimetallic units can be controlled. The intramolecular coupling between the Ni II ( S = 1) ions was found to be ferromagnetic ( J = +4.0 ± 0.5 cm −1 ) in the case of [L 1 Ni 2 (N 3 )(NO 3 ) 2 ] ( 1 ) with a μ‐1,1 azide, but antiferromagnetic ( J = −25.7 ± 0.3 cm −1 ) for [L 2 Ni 2 (N 3 )](ClO 4 ) 2 ( 2 ) with a μ‐1,3 azide. Such bimetallic units can serve as building blocks for the construction of high‐nuclearity Ni II /azide compounds, as demonstrated for the tetranuclear complexes [L 1 2 Ni 4 (μ‐1,1‐N 3 ) 2 (μ‐1,3‐N 3 ) 2 ](BPh 4 ) 2 ( 3 ), and [L 3 Ni 2 (N 3 ) 3 ] 2 ( 4 ). Complex 3 was obtained by the replacement of the labile nitrates in 1 by additional azido ligands, that bridge the two [L 1 Ni 2 (N 3 )] 2+ subunits in the μ‐1,3 mode. Complex 4 incorporates two additional azides, and two of its azido linkages were found in the rare μ‐1,1,3 binding mode (albeit with relatively long Ni−N bond lengths). The magnetic properties of the tetranuclear species were as predicted from the building blocks and the respective azide binding, with ferromagnetic intra‐dimer and antiferromagnetic inter‐dimer exchanges, yielded an overall S = 0 ground state. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2004)