title: Interplay of magnetic exchange interactions and Ni-S-Ni bond angles in polynuclear nickel(II) complexes.
abstract: The ability of bridging thiophenolate groups (RS(-)) to transmit magnetic exchange interactions between paramagnetic Ni(II) ions is examined. Specific attention is paid to complexes with large Ni-SR-Ni angles. For this purpose, dinuclear [Ni(2)L(1)(mu-OAc)I(2)][I(5)] (2) and trinuclear [Ni(3)L(2)(OAc)(2)][BPh(4)](2) (3), where H(2)L(1) and H(2)L(2) represent 24-membered macrocyclic amino-thiophenol ligands, are prepared and fully characterized by IR- and UV/Vis spectroscopy, X-ray crystallography, static magnetization M measurements and high-field electron spin resonance (HF-ESR). The dinuclear complex 2 has a central N(3)Ni(2)(mu-S)(2)(mu-OAc)Ni(2)N(3) core with a mean Ni-S-Ni angle of 92 degrees . The macrocycle L(2) supports a trinuclear complex 3, with distorted octahedral N(2)O(2)S(2) and N(2)O(3)S coordination environments for one central and two terminal Ni(II) ions, respectively. The Ni-S-Ni angles are at 132.8 degrees and 133.5 degrees . We find that the variation of the bond angles has a very strong impact on the magnetic properties of the Ni complexes. In the case of the Ni(2)-complex, temperature T and magnetic field B dependencies of M reveal a ferromagnetic coupling J=-29 cm(-1) between two Ni(II) ions (H=JS(1)S(2)). HF-ESR measurements yield a negative axial magnetic anisotropy (D<0) which implies a bistable (easy axis) magnetic ground state. In contrast, for the Ni(3)-complex we find an appreciable antiferromagnetic coupling J'=97 cm(-1) between the Ni(II) ions and a positive axial magnetic anisotropy (D>0) which implies an easy plane situation.
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW Dresden, 01171 Dresden, Germany. y.krupskaya@ifw-dresden.de
authors.forename: Yulia
authors.initials: Y
authors.lastname: Krupskaya
authors.forename: Alexey
authors.initials: A
authors.lastname: Alfonsov
authors.forename: Anupama
authors.initials: A
authors.lastname: Parameswaran
authors.forename: Vladislav
authors.initials: V
authors.lastname: Kataev
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Klingeler
authors.forename: Gunther
authors.initials: G
authors.lastname: Steinfeld
authors.forename: Norman
authors.initials: N
authors.lastname: Beyer
authors.forename: Mathias
authors.initials: M
authors.lastname: Gressenbuch
authors.forename: Berthold
authors.initials: B
authors.lastname: Kersting
authors.forename: Bernd
authors.initials: B
authors.lastname: Büchner