Synthesis, Characterization, and Spontaneous Resolution of Chiral Nickel(II) Complexes with the Tripod Ligand Tris[2-(((2-phenylimidazol-4-yl)methylidene)amino)ethyl]amine

The chiral nickel(II) complexes of a tripod-type ligand with the chemical formulas [Ni(H3L)](NO3)2·MeOH (1),
[Ni(H3L)](ClO4)2·MeOH (2), and [Ni(H3L)](C6H5COO)2·6H2O (3) were synthesized and characterized (H3L =
tris[2-(((2-phenylimidazol-4-yl)methylidene)amino)ethyl]amine). The crystal structures of 1−3 were determined
by their single-crystal X-ray analyses. 1, C37H40N12O7Ni:  orthorhombic, P212121; a = 14.198(2) Å, b = 22.422(2)
Å, c = 12.019(2) Å, Z = 4. 2, C37H40N10O9Cl2Ni:  orthorhombic, P212121; a = 14.206(2) Å, b = 22.735(3) Å,
c = 12.696(3) Å, Z = 4. 3, C50H58N10O10Ni:  triclinic, P1̄; a = 14.191(5) Å, b = 16.048(4) Å, c = 13.692(4) Å,
α = 115.25(2)°, β = 111.07(3)°, γ = 64.75(2)°, Z = 2. Each complex has an octahedral coordination environment
for the nickel(II) ion, formed by the six nitrogen donor atoms, and is either a Δ (clockwise) or a Λ (anticlockwise)
enantiomorph, depending on the screw arrangement of the tripod-type ligand around the nickel(II) ion. The circular
dichroism (CD) spectrum of a powdered sample of a crystal of 1 showed a positive and a negative peak at 915
and 630 nm, respectively, and that of another crystal showed an enantiomeric pattern. The observation of the
Cotton effect and the crystal structure provided evidence for spontaneous resolution of the chiral complex molecule.