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](BPh4)(2) (2 ). where (L-2)(2-) represents the dianionic form of the 'N4S2' ligand N.N'- bis(2-thio-3-aminomethyl-5-tert-butylbenzyl)- propane- 1,3-diamine), has be en investigated with respect to its ability to function as a building block for the preparation of polynuclear nickel complexes with a high-spin groun d state. Treatment of 2 with pyridazine (pydz) followed by addition of two equivalents of NH4SCN afforded the dinuclear mu -pyridazine complex [(L-2)N i-2(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 [{(L-2)Ni-2(mu -pydz)(N-3)}(2)](BPh4)(2) (5). Both complexes have been characterized by X -ray crystallography and variable -temperature magnetic susceptibility stud ies. In complex 4 two fac(SCN)N2Ni1I units are linked by two thiophenolate sulfur atoms and a mu -pydz ligand to give a (SCN)N2Ni(mu -S)(2)(mu- pydz)N iN2(NCS) core structure with a pseudoconfacial bioctahedral geometry. The t wo NCS- groups occupy opposite coordination sites, each is in a cis positio n to the pydz bridge. Analyses of the susceptibility data indicate the pres ence of an intramolecular ferromagnetic exchange interaction between the tw o Ni-11 (S= 1) ions. Complex 5 is composed of two binuclear [(L-2)Ni-2(mu - pydz)](2+) subunits which are linked by two azide ions to give a rectangula r array of four six-coordinate Ni-11 ions. The binuclear [(L-2)Ni-2(eta -py dz)](2+) fragments in 4 and 5 are isostructural. Analyses of the susceptibi lity data of 5 reveal ferromagnetic exchange interactions between the Ni-11 ions of the binuclear subunit as well as for the N(3)bridged N-11 ions. Th us, compound 4 has an S - 2 ground state, whereas in 5 it is S=4.