title: Structural variety and magnetic properties of tetranuclear nickel(II) complexes with a central mu4-azide.
abstract: Using a set of pyrazolate-based dinucleating ligands with thioether sidearms and a set of different carboxylates, seven tetranuclear nickel(II) complexes of types [L2Ni4(N3)3(O2CR)2](ClO4) (1) and [L2Ni4(N3)(O2CR)4](ClO4) (2) featuring an unprecedented central mu4-1,1,3,3-azide could be isolated and fully characterized. X-ray crystal structures are discussed for 1a,b,e and 2b. The mu4-1,1,3,3-azide is symmetric in all cases except 1a but exhibits distinct binding modes with significantly different Ni-N(azide)-Ni angles and Ni-NNN-Ni torsions in type 1 and 2 complexes, which indicates high structural flexibility of this novel bridging unit. Also, IR-spectroscopic signatures and magnetic properties are distinct for type 1 and 2 complexes. Magnetic data for 1a,b,d,e and 2a,b were investigated and analyzed in a three-J approach. The only model that gave a satisfactory fit for all type 1 complexes includes one dominant antiferromagnetic coupling and two ferromagnetic interactions (one large and one smaller), indicating some degree of frustration. On the basis of magneto-structural correlations for end-on and end-to-end azide linkages, it is reasonable to assign the antiferromagnetic interaction to the intradimer exchange along the pyrazolate and the end-to-end linkage of the mu4-azide. Overall, the magnitude of the coupling constants differs significantly for the two distinct types of compounds, 1 or 2, and depends on the individual geometric details of the Ni4 array and the mu4-1,1,3,3-azide.
authors.affiliation: Institut für Anorganische Chemie, Georg-August-Universität, Tammannstrasse 4, D-37077 Göttingen, Germany.
authors.forename: Serhiy
authors.initials: S
authors.lastname: Demeshko
authors.forename: Guido
authors.initials: G
authors.lastname: Leibeling
authors.forename: Walter
authors.initials: W
authors.lastname: Maringgele
authors.forename: Franc
authors.initials: F
authors.lastname: Meyer
authors.forename: Christopher
authors.initials: C
authors.lastname: Mennerich
authors.forename: Hans-Henning
authors.initials: HH
authors.lastname: Klauss
authors.forename: Hans
authors.initials: H
authors.lastname: Pritzkow