Crystal structure of [bis(acetonitrile κ¹N)-bis(μ₂-3,3′-methylenebis(1-methyl-1,3-dihydro-2H-imidazole-2-thione)-κ²S,S)iron(II) diperchlorate], C₂₂H₃₀Cl₂FeN₁₀O₈S₄

1 Source of material

The title complex [Fe(C₉H₁₂N₄S₂)₂(CH₃CN)₂](ClO₄)₂ was synthesized by a direct synthesis. All reagents used were purchased from commercial sources and used without further purification. The 3,3′-methyl-enebis(1-methyl-1,3-dihydro-2H-imidazole-2-thione)methane (C₉H₁₂N₄S₂, abbreviated as mbit) was synthesized by the previously reported route. ^{4 , 5 , 6} A mixture of FeCl₂ (63 mg, 0.5 mmol) and Ag(ClO₄)₂ (210 mg, 1 mmol) was dissolved in 10 mL CH₃CN in a N₂ atmosphere, stirred, then filtered to remove solid substances after the reaction was complete. Also under N₂ atmosphere, mbit (240 mg, 1 mmol) was added to the filtrate, and stirring was performed for 8 h. Red rod shaped crystals were obtained by slowly evaporating the filtrate at room temperature.

2 Experimental details

The structure was solved by Direct Methods and refined with the Olex ^{1 , 2} and SHELXL ³ software package. The figure of the title crystal structure was drawn by the Diamond software. ⁷ Hydrogen atoms attached to C were positioned geometrically and refined as riding atoms. The U _iso values were set to be 1.5U _eq (C) of the carrier atom for methyl H atoms and 1.2U _eq (C) for the remaining H atoms.

3 Comment

The structures of organic ligands usually play a decisive role in the configuration and properties of metal complexes. Therefore, in the synthesis process of functional metal complexes, it is very necessary to choose appropriate ligands. As a bidentate sulfur-containing ligand, mbit is often chosen to construct zero dimensional, one-dimensional, or three-dimensional complexes. ^{4 , 8 , 9 , 10 , 11 , 12 , 13} The S atoms in mbit can sometimes act as bridging atoms to form multinuclear complexes. ^{10 , 14} In the research process of transition metal complexes, iron has attracted much attention due to its abundant natural reservers, diverse coordination forms, excellent biocompatibility, and outstanding light absorption properties. Therefore, we designed and synthesized a new six coordinated mononuclear iron (II) complex with mbit as the ligand, and the crystal structure of this complex was tested.

X-ray crystallography analyses reveal that the asymmetric unit of the title complex contains one half of a Fe(II) cation, one mbit ligand, one CH₃CN ligand located on a two-fold axis. One perchlorate counter anion is located in a general position of the space group Pccn. The Fe(II) ion is coordinated by two nitrogen atoms and four sulfur atoms. The two N atoms are derived from acetonitrile molecules, and the four sulfur atoms are derived from two mbit molecules. Both Fe–N bond distances are 2.207(3) Å, this value agrees well with previously reported Fe(II) complexes. ^{15 , 16 , 17} The Fe–S bond distances are 2.5157(12) and 2.5359(11) Å, respectively. These bond distances are slightly longer than those of the reported Fe(II) polymers with mbit as ligands. ⁹ In those polymers [L¹FeCl₂] _n (L¹ = bis(3-methyl-2-thione-imidazolyl) methane) and [L²FeCl₂] _n (L² = bis(3-tert-butyl-2-thione- imidazolyl)methane), the Fe–S bond distances are in the range of 2.3725(5)–2.3906(5) Å. ⁹ The angles in the acetonitrile molecule and the metal-to-ligand bond are nearly linear (Bond angles: N5–C10–C11 is 178.8(5)^°, Fe–N5–C10 is 174.8(3)^°). In this complex, four N atoms from the same mbit ligand surround one N atom from the acetonitrile ligand, and these five N atoms are almost in the same plane. The angle of two such planes (plane1: N1, N2, N3#1, N4#1, N5#1; plane2: N1#1, N2#1, N3, N4, N5) is 83.7^°. The shortest distance of the adjacent Fe(II) ions is 7.4590(27) Å. The stable packing of the title complex is mainly due to the presence of weak hydrogen bonding interactions of S···H bond (C(5)–H(5A)···S(1), 2.77 Å; C(5)–H(5A)···S(2)#2, 2.80 Å, #2: -x, -y, -z) and O⋯H bond (C(7)–H(7)···O(2)#3, 2.51 Å, #3: −1/2−x, 1+y, −1/2+z; C(8)–H(8)···S(3)#4, 2.55 Å, #4: 1/2+x, −y, 1/2−z; and C(11)–H(11B)⋯O(1)#5, 2.54 Å, #5: 1/2−x, 3/2−y, 1+z), forming a three dimensional network. It is worth noting that the structure of this iron complex is different from the Sn(IV) complex reported in 1998. ¹⁸ Although both complexes are six coordinated, and in each complex the two mbit molecules acting as bidentate chelating ligands through the sulfur atoms, in the Sn(IV) cation, the metal atom lying on a symmetry centre exhihits a slightly distorted octahedral coordination with the iodides at the apices in trans position. In the title complex, two acetonitrile molecules are in adjacent positions, the bond angle of N5–Fe–N5#1 is 83.82(17)^°.

In order to evaluate the deviation degrees of the FeS₄N₂ moiety in the title complex from the ideal symmetry, continuous shape measurement analyses was performed using the Shape 2.1 program. ^{19 , 20} The calculated deviation parameters provide an estimation of the deviation from the ideal structure with 0 corresponding to the ideal polyhedron. The calculation result are as follows: Hexagon, 30.272; Pentagonal pyramid, 27.291; Octahedron, 0.537; Trigonal prism, 15.609; Johnson pentagonal pyramid J2, 31.195). According to the calculation results, the configuration of the FeS₄N₂ moiety in the title complex shows a slightly distorted octahedral configuration. In general the geometrical parameters are in the expected ranges. ²¹