Binuclear complexes as building blocks for polynuclear complexes with high-spin ground states: synthesis and structure of a tetranuclear nickel complex with an S = 4 ground state.

Abstract

The coordinatively unsaturated dinickel(II) complex [(L2)Ni2](BPh4)2 (2), where (L2)2- represents the dianionic form of the 'N4S2' ligand N,N'-bis(2-thio-3-aminomethyl-5-tert-butylbenzyl)propane-1,3-diamine), has been investigated with respect to its ability to function as a building block for the preparation of polynuclear nickel complexes with a high-spin ground state. Treatment of 2 with pyridazine (pydz) followed by addition of two equivalents of NH4SCN afforded the dinuclear mupyridazine complex [(L2)Ni2(mu-pydz)(NCS)2] (4). The reaction of 2 with pyridazine and NaN3 in a 1:1:1 molar ratio gave the tetranuclear nickel(II) complex [[(L2)Ni2(mu-pydz)(N3)]2](BPh4)2 (5). Both complexes have been characterized by X-ray crystallography and variable-temperature magnetic susceptibility studies. In complex 4 two fac(SCN)N2Ni(II) units are linked by two thiophenolate sulfur atoms and a mu-pydz ligand to give a (SCN)N2Ni(mu-S)2(mu-pydz)NiN2(NCS) core structure with a pseudoconfacial bioctahedral geometry. The two NCS- groups occupy opposite coordination sites, each is in a cis position to the pydz bridge. Analyses of the susceptibility data indicate the presence of an intramolecular ferromagnetic exchange interaction between the two Ni(II) (S = 1) ions. Complex 5 is composed of two binuclear [(L2)Ni2(mu-pydz)]2+ subunits which are linked by two azide ions to give a rectangular array of four six-coordinate Ni(II) ions. The binuclear [(L2)Ni2(mu-pydz)]2+ fragments in 4 and 5 are isostructural. Analyses of the susceptibility data of 5 reveal ferromagnetic exchange interactions between the Ni(II) ions of the binuclear subunit as well as for the mu(1,3)N3-bridged Ni(II) ions. Thus, compound 4 has an S = 2 ground state, whereas in 5 it is S = 4.