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

The coordinatively unsaturated dinickel( II ) complex [(L 2 )Ni 2 ](BPh 4 ) 2 ( 2 ), where (L 2 ) 2− represents the dianionic form of the 'N 4 S 2 ' 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 NH 4 SCN afforded the dinuclear μ ‐pyridazine complex [(L 2 )Ni 2 ( μ ‐pydz)(NCS) 2 ] ( 4 ). The reaction of 2 with pyridazine and NaN 3 in a 1:1:1 molar ratio gave the tetranuclear nickel( II ) complex [{(L 2 )Ni 2 ( μ ‐pydz)(N 3 )} 2 ](BPh 4 ) 2 ( 5 ). Both complexes have been characterized by X‐ray crystallography and variable‐temperature magnetic susceptibility studies. In complex 4 two fac ‐(SCN)N 2 Ni II units are linked by two thiophenolate sulfur atoms and a μ ‐pydz ligand to give a (SCN)N 2 Ni( μ ‐S) 2 ( μ ‐ pydz )NiN 2 (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 [(L 2 )Ni 2 ( μ ‐pydz)] 2+ subunits which are linked by two azide ions to give a rectangular array of four six‐coordinate Ni II ions. The binuclear [(L 2 )Ni 2 ( μ ‐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 μ 1,3 ‐N 3 ‐bridged Ni II ions. Thus, compound 4 has an S =2 ground state, whereas in 5 it is S =4.