Tetranuclear nickel complexes composed of pairs of dinuclear LNi 2 fragments linked by 4,4′-bipyrazolyl, 1,4-bis(4′- pyrazolyl)benzene, and 4,4′-bipyridazine: Synthesis, structures, and magnetic properties

Vasile Lozan, Pavlo Y. Solntsev, Guido Leibeling, Konstantin V. Domasevitch, Berthold Kersting

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Abstract

The ability of the ligands 4,4′-bipyrazolyl (H 2bpz), 1,4-bis(4′-pyrazolyl)benzene (H 2bpzb), and 4,4′- bipyridazine (bpdz) to link two dioctahedral LNi 2 units has been examined. The following complexes were prepared: [L 1Ni II 2(Hbpz)][BPh 4] (6[BPh 4]), [L 1Ni II 2(bpdz)][ClO 4] 2 (7[ClO 4] 2), [(L 1Ni II 2) 2(bpzb)]-[BPh 4] 2 (8[BPh 4] 2), and [(L 2Ni II 2) 2(bpz)][BPh 4] 2 (9[BPh 4] 2), where (L 1) 2- and (L 2) 2- represent macrocychc hexaaza-dithiophenolate ligands. All complexes have been characterised by UV/Vis spectroscopy, IR spectroscopy, and X-ray crystallography. Whereas (Hbpz) - and bpdz in 6[BPh 4] 2 and 7[ClO 4] 2 act as bidentate ligands coordinating to only one [LNi 2] 2+ unit, in 8[BPh 4] 2 and 9[BPh 4] 2 the (bpzb) 2- and (bpz) 2- units are tetradentate linkers. This is qualitatively explained in terms of the absence or presence of steric repulsions between the tBu groups of the supporting ligands and the length of the coligands. The structures of the tetranuclear complexes differ mainly in the distance between the center of the Ni⋯Ni axes of the isostructural [LNi 2] units {14.040(1) Å in 8[BPh 4] 2, 9.184(1) Å in 9[BPh 4] 2}. The two Ni 2-pyrazolato planes in 9[BPh 4] 2 are coplanar. An analysis of the temperature-dependent magnetic susceptibility data for 9[BPh 4] 2 reveals the presence of weak ferromagnetic exchange interactions between the Ni II ions in the binuclear [L 2Ni 2] subunits with values for the magnetic exchange constant J 1 of 23.97 cm -1 (H = -2JS 1S 2). The exchange coupling across the dipyrazolato bridge is less than 0.1 cm -1, suggesting that no significant interdimer exchange coupling occurs in 9[BPh 4] 2.

Original languageEnglish (US)
Pages (from-to)3217-3226
Number of pages10
JournalEuropean Journal of Inorganic Chemistry
Issue number20
DOIs
StatePublished - 2007

Keywords

  • Bipyrazolate ligands
  • Macrocyclic ligands
  • Magnetic properties
  • Nickel
  • Polynuclear complexes

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