The synthesis and structural characterization of three compounds containing three-coordinate Fe(II) and stabilized by sterically encumbered thiolate ligands are reported. Reaction of [Fe2(SC6H2-2,4,6-t-Bu3)4] (3) with LiSC6H2-2,4,6-t-Bu3 in ether/THF/hexane afforded [Li(THF)2(5)] 0.5C6H14 (5 = [Fe(SC6H2-2,4,6-t-Bu3)3]−). Addition of Ph4PCl to a reaction mixture in toluene followed by recrystallization of the product from acetonitrile yielded (Ph4P) 2MeCN C7H8. The compound [Fe3(SC6H2-2,4,6-t-Pr3)4(N(SiMe3)2)2] was prepared by the reaction of [Fe(N(SiMe3)2)2] (6) with the thiol in toluene. [Li(THF)2(5)] 0.5C6H14 crystallizes in monoclinic space group P21/c with a = 9.809(2) Å, b = 22.507(5) Å, c = 29.553(5) Å, ß = 95.72(2)°, and Z = 4 (130 K). (Ph4P)- 2MeCN-C7H8 was obtained in monoclinic space group P21 with a = 17.538(5) Å, b = 14.912(4) Å, c = 17.608(5) Å, ß = 115.71(3)°, and Z = 2 (143 K). These compounds contain the first example of mononuclear Fe(II) in a close approach to a trigonal planar  or a distorted trigonal planar [Li(THF)2(5)] sulfur coordination environment. In the Ph4P salt,  exhibits the mean values Fe-S = 2.274(9) Å and S-Fe-S = 120(3)°, while in [Li(THF)2(5)] the Li+ ion bridges two sulfur atoms, causing a lengthening (0.06–0.07 Å) of the Fe-S bridged bond lengths and constriction of the bridged S-Fe-S angle (92.2(1)°). Compound 6 crystallizes in P21/c with a = 14.521(5) Å, b = 41.60(2) Å, c = 14.241(4) Å, ß = 100.42(2)°, and Z = 4 (130 K). The structure has a linear Fe3(μ2-SR)4 fragment with an almost linear Fe3 array involving the central Fe(II) atom in a severely distorted tetrahedral environment; the terminal Fe(II) atoms are three-coordinate and planar with terminal N(SiMe3)2 ligands. Complex 5 expands the family of homoleptic molecular Fe(II) thiolates to five structural types; complexes 5 and 6 with two previously reported species of the type [Fe2(SR)4] constitute the known examples of three-coordinate FeII with partial or complete sulfur ligation. The zero-field Mössbauer spectra of examples of the five types of homoleptic Fe(II) thiolates are reported together with several tetrahedral complexes having FeII-S/SR coordination in order to determine what structural distinctions could be made from isomer shifts and quadrupole splittings. From the limited data set, it is tentatively concluded that trigonal planar FeII(SR)3 can be distinguished from tetrahedral FeII(SR)4 and FeII-S/SR units on the basis of its smaller quadrupole splitting (0.81 mm/s for 5 at 4.2–100 K).
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry