Mononuclear, dinuclear and pentanuclear Fe(II) complexes of an N3S ligand

The mixed N3S(thiolate) ligand 1-bis2-(pyridin-2-yl)ethylamino-2-methylpropane-2-thiol (Py2SH) was used in the synthesis of four iron(II) complexes: (Py2S)FeCl (1), (Py2S)FeBr (2), (Py2S)4Fe5II(mu-OH)2(BF4)4 (3), and (Py2S)2Fe2II(mu-OH)BF4 (4). The X-ray structures of 1 and 2 revealed monomeric iron(II)-alkylthiolate complexes with distorted trigonal-bipyramidal geometries. The paramagnetic 1H NMR spectra of 1 and 2 display resonances from delta = -25 ppm to +100 ppm, consistent with a high-spin iron(II) ion (S = 2). Spectral assignments were made on the basis of chemical shift information and T1 measurements and show the monomeric structures are intact in solution. To provide entry into hydroxide-containing complexes, a novel synthetic method was developed involving strict aprotic conditions and limiting amounts of H2O. Reaction of Py2SH with NaH and Fe(BF4)2.6 H2O under aprotic conditions led to the isolation of the pentanuclear, mu-OH complex 3, which has a novel dimer-of-dimers type structure connected by a central iron atom. Conductivity data on 3 show this structure is retained in CH2Cl2. Rational modification of the ligand-to-metal ratio allows control over the nuclearity of the product, yielding the dinuclear complex 4. The X-ray structure of 4 reveals an unprecedented face-sharing, biooctahedral complex with an S2O bridging arrangement. The magnetic properties of 3 and 4 in the range 1.9-300 K were successfully modeled. Dinuclear 4 is antiferromagnetically coupled J = -18.8(2) cm(-1). Pentanuclear 3 exhibits ferrimagnetic behavior, with a high-spin ground state of S(T) = 6, and was best modeled with three different exchange parameters J = -15.3(2), J' = -24.7(3), and J'' = -5.36(7) cm(-1). DFT calculations provided good support for the interpretation of the magnetic properties.