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

The mixed N 3 S(thiolate) ligand 1‐[bis{2‐(pyridin‐2‐yl)ethyl}amino]‐2‐methylpropane‐2‐thiol (Py 2 SH) was used in the synthesis of four iron( II ) complexes: [(Py 2 S)FeCl] ( 1 ), [(Py 2 S)FeBr] ( 2 ), [(Py 2 S) 4 Fe 5 II (μ‐OH) 2 ](BF 4 ) 4 ( 3 ), and [(Py 2 S) 2 Fe 2 II (μ‐OH)]BF 4 ( 4 ). The X‐ray structures of 1 and 2 revealed monomeric iron( II )–alkylthiolate complexes with distorted trigonal‐bipyramidal geometries. The paramagnetic 1 H NMR spectra of 1 and 2 display resonances from δ =−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 T 1 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 H 2 O. Reaction of Py 2 SH with NaH and Fe(BF 4 ) 2 ⋅6 H 2 O under aprotic conditions led to the isolation of the pentanuclear, μ‐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 CH 2 Cl 2 . 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 [S 2 O] 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.