Monomere Komplexe NiL mit vierzähnigen Liganden [R2P(S)N–R'–NP(S)R2]2– (= L) [1]

Monomeric Complexes NiL with Tetradentate Ligands R₂P(S)N–R'–NP(S)R₂]^2– (= L) Metathesis of NiCl₂(PPh₃)₂] with Li salts of the potentially tetradentate ligands R₂P(S)N–R'–NP(S)R₂]^2– (= L) affords monomeric complexes NiL containing the chromophore NiN₂S₂ ( 1 : R = Et; a , b : R' = Me₂C–(CH₂)₂–CMe₂, o-Phenylen; 2 : R = t-Bu, R' = (CH₂)_n; a – c : n = 2, 3, 4). According to the results of magnetic measurements and VIS as well as NMR spectroscopy (¹H, ³¹P) these complexes are planar except 1 a that is tetrahedral. In case of 1 a and 2 c this was confirmed by the results of crystal structure analyses. In toluene, however, 1 a and 2 c form an equilibrium of planar (diamagnetic) and tetrahedral (paramagnetic) conformers. VT-¹H-NMR including ¹H,¹H-COSY showed a hindered Δ,Λ-inversion of 1 a below 330 K. Only with 1 b a pentacoordinate adduct 1 b · PPh₃ was obtained that completely dissociates in its components on dissolving in benzene. 1 a and 2 c crystallize in the monoclinic space group P2₁/c containing 4 molecules in the unit cell of the dimensions 1 a : a = 8.774(1), b = 12.335(2), c = 21.339(3) Å, β = 92.33(1)° and 2 c : a = 13.374(8), b = 16.197(8), c = 12.814(6) Å, β = 109.20(4)°. The coordination of the Ni atom yields in 1 a a dihedral angle ϵ of 41.7(1)° and thus a geometry intermediate between planar and tetrahedral while in 2 c the angle of 4.5(1)° reveals a nearly planar chromophore NiN₂S₂.