THIOETHER BINDING OF LOW-SPIN BIVALENT MANGANESE - A MS(2)N(4) FAMILY FURNISHED BY NEW HEXADENTATE THIOETHER-OXIME-AZO LIGANDS (M=MN-II, FE-II, FE-III)

Four hexadentate ligands of type HON=C(R)N=NC6H4S(CH2)(x)SC6H4N=NC(R)=NOH (x = 2, 3; R = Ph, alpha-naphthyl) abbreviated as H(2)RxL have been synthesized. These have afforded the low-spin complexes Mn-II(RxL) (1.84-1.88 mu(B)), Fe-II(RxL)(diamagnetic), and [Fe-III(RxL)]ClO4 (1.92-2.10 mu(B)). X-ray structure determination of Mn-II(Ph3L) has revealed the presence of a distorted octahedral MnS2N4 coordination sphere. The metal atom lies on a two-fold axis of symmetry. The Mn-N (1.900(12) Angstrom, 1.923(10) Angstrom) and the Mn-S (2.350(5) Angstrom) lengths are much shorter than those in comparable thioether ligated high-spin manganese(II) species. Metal-ligand back-bonding is proposed to be present in Mn(Ph3L). Its magnetic moment decreases slightly with decreasing temperature as expected for the low-spin 3d(5) configuration with substantially quenched orbital moment. In fluid solution, Mn(RxL) species exhibit six-line EPR spectra with a relatively low hyperfine constant (70-71 G). In frozen dichloromethane-toluene (77 K) solution anisotropic spectra are observed for both Mn(RxL) and Fe(RxL)(+). Oximato-N binding is an effective tool for inducing low-spin character. Crystal data for Mn(Ph3L) are the following: crystal system orthorhombic, space group Pbna, a = 8.753(5) Angstrom, b = 14.575(7) Angstrom, c = 21.297(12) Angstrom, V = 2717(2) Angstrom(3), Z = 4, R = 6.85%, R(W) = 6.21%.