Ligand-Based Redox Isomers of [Zn(II)(C(28)H(40)NO(2))(2)]: Molecular and Electronic Structures of a Diamagnetic Green and a Paramagnetic Red Form.

The tridentate trianion of N,N-bis(2-hydroxy-di-3,5-tert-butylphenyl)amine, H(3)L(3), forms 1:1 and 2:1 complexes with di-, tri-, or tetravalent transition metal ions where it can exist in four oxidation levels (C(28)H(40)NO(2))(3)(-)(,2)(-)(,1)(-)(,0), which are herein designated as L(3), L(2), L(1), and L(0), respectively; (L(2))(2)(-) and (L(0))(0) are paramagnetic (S = (1)/(2)), whereas the other two are diamagnetic (S = 0). We have synthesized the complexes [Zn(L(2))(NEt(3))] (1), green [Zn(L(1))(2)] (2), and red [Zn(L(2))(L(0))] (3). Complexes 1, 2 (Girgis, A. Y.; Balch, A. L. Inorg. Chem. 1975, 14, 2724), and 3 have been characterized by X-ray crystallography: 1, orthorhombic, Iba2, a = 23.194(4) Å, b = 25.132(4) Å, c = 11.741(2) Å, V = 6844(2) Å(3), Z = 8; 2, orthorhombic, C222(1), a = 19.494(3) Å, b = 24.065(4) Å, c = 23.458(4) Å, V = 11004(3) Å(3), Z = 8; 3, triclinic, P&onemacr;, a = 11.677(2) Å, b = 12.192(2) Å, c = 20.522(3) Å, alpha = 83.68(2), beta = 74.37(2), gamma = 75.40(2)(o), V = 2720.0(8) Å(3), Z = 2. Complexes 1 and 3 are paramagnetic with one and two (uncoupled) unpaired electrons per zinc ion (3-290 K), respectively, whereas 2 is diamagnetic. Complexes 2 and 3 are shown to be ligand-based redox isomers. Red 3 converts into the green form 2 in tetrahydrofuran solution under anaerobic conditions via an intramolecular process (k = 0.7 x 10(-)(3) s(-)(1) at 23 degrees C; DeltaH() = 15.6 +/- 0.6 kcal mol(-)(1), DeltaS() = -20.4 +/- 1.8 cal mol(-)(1) K(-)(1)). The electronic structures of 1 and 3 have been investigated by X-band EPR and (1)H NMR spectroscopy. The electro-, spectroelectrochemistry, and magnetochemistry of all complexes are reported.