A series of bis(N-alkylsalicylaldiminato)nickel(II) complexes Ni(XYsal-R) = NiA(2) with different combinations of substituents X (= tert-butyl, isopropyl, isobutyl, NO2, Br), Y (= methyl, H), and alkyl groups R (= H, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, neopentyl) were prepared and characterized by their vis/near-IR absorption spectra and magnetic moments (XYsal-R = anion of N-alkyl-3-X-5-Y-salicylaldimine). X-ray structure analysis of Ni(3-tert-butyl-5-methylsal-Et)(2) (= C28H40N2O2Ni; monoclinic, P2(1)/c; alpha = 12.188(4), b = 11.455(4), and c = 18.852(6) Angstrom, beta = 97.66(1)degrees; Z = 4; R(w) = 0.0367) and of the corresponding Zn(II) complex (= C28H40N2O2Zn; monoclinic, C2/c; alpha = 27.14(2), b = 13.17(1), and c = 18.30(2) Angstrom, beta = 120.64(2)degrees; Z = 8; R(w) = 0.0357) confirms a distorted planar geometry of the NiN2O2 coordination core and tetrahedral coordination of the zinc. The equilibrium constants K-1 and K-2 for the formation of the various pyridine adducts NiA(2) . py and NiA(2) . 2py, respectively, were determined by spectrophotometric titration in acetone. Variable-temperature H-1 NMR measurements led to the equilibrium constants K-p,K-r for the fast configurational isomerization of complexes NiA(2) in organic solution according to NiA(2) (planar) reversible arrow NiA(2) (tetrahedral).