Mononuclear, Dinuclear, and Pentanuclear (N,S(thiolate))Iron(II) Complexes: Nuclearity Control, Incorporation of Hydroxide Bridging Ligands, and Magnetic Behavior

The mixed N3S(thiolate) ligand 1-[bis{2-(pyridin-2-yl)ethyl}amino]- 2-methylpropane-2-thiol (Py2SH) was used in the synthesis of four iron(ii) complexes: [(Py2S)FeCl] (1), [(Py2S)FeBr] (2), [(Py2S)4Fe5 II(m-OH)2]- (BF4)4 (3), and [(Py2S)2Fe2 II(m-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 d=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)2·6H2O under aprotic conditions led to the isolation of the pentanuclear, m-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) cm1]. Pentanuclear 3 exhibits ferrimagnetic behavior, with a highspin ground state of ST=6, and was best modeled with three different exchange parameters [J=15.3(2), J’= 24.7(3), and J’’=5.36(7) cm1]. DFT calculations provided good support for the interpretation of the magnetic properties.