Reaction of LLi with metal halides or metal halide complexes affords chelate complexes LnM (L = R2P(NR')2-; M = Cr3+, Co2+, Ni2+, Zn2+). With the bulky ligand t-Bu2P(NSiMe3)2- and Ni(PPh3)2Cl2 or Ni(dme)Br2 (dme = dimethoxyethane) only halide bridged chelates [LNiX]2 (X = Cl, Br) contg. tetrahedral chromophores NiN2X2 were obtained. Main objects of investigation were the bischelates L2Ni (I). I with R = i-Pr, R' = Me and R = Ph, R' = Et are planar, with R = i-Pr, R' = Et and R, R' = i-Pr, i-Pr; Ph, i-Pr; Et, SiMe3, Ph, SiMe3 tetrahedral. In solns. of I (R = i-Pr, R' = Et) and I (R = Ph, R' = Et) a conformational equil. planar (diamagnetic) .dblharw. tetrahedral (paramagnetic) exists that is shifted to the right with increasing temp. and is dominated by the tetrahedral I (R = i-Pr, R' = Et) or planar conformer I (R = Ph, R' = Et) at room temp. As is the case with the isovalence electronic compds. [R2P(S)NR']2Ni small substituents R' apparently favor the planar state and in contrast to some complexes [R2P(O)NR']2Ni no paramagnetic planar species I have yet been obsd. These findings that are derived from the results of magnetic measurements and of UV/VIS as well as NMR spectroscopy are confirmed by crystal structure detns.: I (R = i-Pr, R' = Me) was found to be planar (orthorhombic, space group P212121, a = 3382.8(11), b = 1124.0(4), c = 8874(3), V = 3374.2(17) .ANG.3, Z = 6, rc = 1.611 g/cm3, m(MoKa) = 1.35 mm-1, 2594 obsd. reflections with Fo >= 4s(Fo), 320 refined parameters, R = 0.0467, Rw = 0.0516), and I (R = Ph, R' = SiMe3) to be tetrahedral (monoclinic, space group P21/n, a = 1268.4(2), b = 1806.8(2), c = 1971.6(2), V = 4331.0(11) .ANG.3, Z = 4, rc = 1.288 g/cm3, m(MoKa) = 0.74 mm-1, 4900 obsd. reflections with Fo >= 4s(Fo), 378 refined parameters, R = 0.0556, Rw = 0.0570). The bite angle NNiN of the chelate ligand in I (R = i-Pr, R' = Me) (~77 Deg) is similar to those in paramagnetic planar complexes [R2P(O)NR']2Ni (NNiO 74-77 Deg) and shows that a small chelate bite does not necessarily imply paramagnetism of planar Ni(II) complexes.