Mixed-chalcogenide double-butterfly complex [{(CO)₆Fe₂SSe}₂{μ-­C(H)—C(H)}]

Bubbling acetyl­ene gas slowly through a methanol solution of [(CO)₆Fe₂{μ-SSe}] containing sodium acetate for 48 h at room temperature yields the double-butterfly complex μ-[ethane-1,1,2,2-tetra(selenido/sulfido)]bis[hexacarbonyldiiron(Fe—Fe)], [Fe₄(C₂H₂S₂Se₂)(CO)₁₂]. The molecular structure was established by single-crystal X-ray diffraction techniques. The structure consists of two Fe₂SSe butterfly units linked to each other through a bridging HC—CH group. The mol­ecule has twofold symmetry and the two Fe atoms have distorted octahedral geometries.

S1. Comment

Bonding and reactivity studies of alkynes attached to metal centres is of considerable interest because of the potential of the coordinated alkynes to be transformed into useful organic species (Katz & Hacker, 1985). In contrast to the large number of reports on the different bonding modes between alkynes and transition metals (Sappa et al., 1985), studies of complexes in which alkynes are attached to main group elements are more recent and relatively few (Mathur, 1997). Recent successes in the area of incorporating group-16 elements into transition metal carbonyl complexes has evoked interest in studying the interaction of alkynes with these ligands. The facile addition of phenylacetylene to (CO)₆Fe₂(µ-Se₂) and (CO)₆Fe₂(µ-EE') occurs at room temperature to form (CO)₆Fe₂{µ-SeC(H)=C(Ph)Se} and (CO)₆Fe₂{µ-EC(H) ═C(Ph)E'} respectively, whereas (CO)₆Fe₂(µ-S₂) and (CO)₆Fe₂(µ-Te₂) are inert towards such addition under similar reaction conditions (Mathur, Hossain et al., 1995). In (CO)₆Fe₂{µ-SeC(H)═C(Ph)Se} the reactive Se sites are blocked, and addition of Pt(PPh₃)₂ (Mathur, Hossain, Das & Sinha et al., 1993) and (CO)₆Fe₂(µ-Se₂) (Mathur & Hossain, 1993) occurs readily across the C=C bond to yield products in which the acetylenic bond is reduced. Similarly, addition of organometallic groups across the Fe—Fe bond can be carried out thermolytically, as in the formation of Se-bridged mixed-metal clusters Cp₂Mo₂Fe₂(CO)₆(µ₄-Se)(µ₃-Se)₂ (Mathur, Hossain & Rheingold, 1993). Here we report the structural characterization of a mixed-chalcogenide double butterfly complex, (I), obtained from the reaction of (CO)₆Fe₂(µ-SSe) with acetylene. The starting material provides an important probe to the active metallic centre in enzymatic processes (Pombeiro & Richards, 1990) \sch

In this structure the Se and S positions are disordered with equal occupany (50%). The molecule contains a twofold axis bisecting the C7—C7' bond. The structure can be described as two Fe₂SSe core units linked to each other through a bridging HC—CH group. As a result of the acetylene addition to the Fe₂SSe tetrahedron, the acetylenic bond is reduced to beyond an olefinic bond order. The C7—C7' bond distance of 1.511 (16) Å in [{(CO)₆Fe₂SSe}₂{µ-C(H)—C(H)}] is similar to that observed in [{(CO)₆Fe₂SSe}₂{µ-C(H)—C(Ph)}] (1.53 (1) Å) (Mathur, Dash et al., 1996), whereas it is longer than the corresponding bond lengths of 1.48 (1) Å in [{(CO)₆Fe₂Se₂}₂{µ-C(H)—C(Ph)}] (Mathur & Hossain, 1993), 1.47 (1) Å in (CO)₆Fe₂{µ-Te(CH₂)₂Te} (Shieh & Shieh, 1994), 1.494 Å in (CO)₆Fe₂{µ-Se(CH₂)₂Se} (Mathur, Manimaran et al., 1996) and 1.42 (1) Å in [(CO)₆Fe₂{µ-SeC(H)—C(Ph)}Pt(PPh₃)₂] (Mathur, Hossain & Rheingold, 1993). Each Fe atom has three CO groups bonded to it. The CO groups, the µ₃-S ligand, the µ₃-Se ligand and the Fe—Fe bond define a distorted octahedral geometry around each Fe centre.

S2. Experimental

In a typical procedure, acetylene gas was bubbled at a slow rate with constant stirring into a methanol solution (15 ml) containing freshly prepared (CO)₆Fe₂(µ-SSe) (0.6 g, 1.53 mmol) (Mathur, Sekar et al., 1995) and anhydrous sodium acetate (0.25 g). The reaction was monitored by thin layer chromatography (TLC) and terminated after 48 h at room temperature, when all the (CO)₆Fe₂(µ-SSe) had been consumed. Chromatographic work up on silica gel TLC plates using 2:3 solution mixture of CH₂Cl₂:hexane yielded an orange band of [{(CO)₆Fe₂SSe}₂{µ-C(H)—C(H)}] in 28% yield. Rectangular-shaped air-stable crystals of [{(CO)₆Fe₂SSe}₂{µ-C(H)—C(H)}] were obtained by slow evaporation from a mixture of CH₂Cl₂/hexane solutions at 263 K. IR data: (ν, CH₂Cl₂) 2080(s), 2068 (s), 2042 (s), 2009 (s), 1997 (m) cm^-1.

S3. Refinement

The data were originally collected in the monoclinic system and the structure solved in space group Cc. Additional symmetry was observed, and the structure was found to transform to the orthorhombic system, space group Fdd2. The Se and S positions were found to be disordered, so their occupancies were fixed at 50% and they were constrained to have the same positional coordinates and the same anisotropic thermal parameters. The hydrogen atom was fixed geometrically and not refined. During refinement, the structure was treated as a racemic twin. The occupancy of the major component refined to a value of 0.515.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: NRCVAX (Gabe et al., 1989); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: NRCVAX; software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. The structure of the title compound showing 30% probability displacement ellipsoids.

(I)

Crystal data

[Fe4(C2H2S2Se2)(CO)12]	Dx = 2.262 Mg m^−3
Mr = 807.60	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Fdd2	Cell parameters from 25 reflections
a = 6.531 (2) Å	θ = 8.0–12.2°
b = 44.759 (4) Å	µ = 5.70 mm^−1
c = 16.224 (2) Å	T = 293 K
V = 4742.6 (16) Å^3	Rectangular, orange
Z = 8	0.38 × 0.13 × 0.13 mm
F(000) = 3088

Data collection

Enraf-Nonius CAD4 diffractometer	2188 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.034
Graphite monochromator	θmax = 27.4°, θmin = 1.8°
ω/2θ scans	h = −8→0
Absorption correction: ψ scan (North et al., 1968)	k = −18→58
Tmin = 0.323, Tmax = 0.488	l = −19→21
6094 measured reflections	3 standard reflections every 60 min
2449 independent reflections	intensity decay: 2%

Refinement

Refinement on F^2	Primary atom site location: heavy-atom
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.108	H-atom parameters constrained
S = 1.10	w = 1/[σ^2(Fo^2) + (0.0473P)^2 + 78.9306P] where P = (Fo^2 + 2Fc^2)/3
2449 reflections	(Δ/σ)max = 0.001
154 parameters	Δρmax = 0.48 e Å^−3
1 restraint	Δρmin = −0.48 e Å^−3

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Se1	0.54003 (17)	0.77886 (2)	−0.05105 (7)	0.0334 (3)	0.5
Se2	0.08860 (15)	0.78785 (2)	−0.00076 (6)	0.0239 (2)	0.5
Fe1	0.32371 (18)	0.82009 (2)	−0.06395 (7)	0.0337 (3)
Fe2	0.39615 (17)	0.79592 (2)	0.07283 (7)	0.0306 (2)
S1	0.54003 (17)	0.77886 (2)	−0.05105 (7)	0.0334 (3)	0.5
S2	0.08860 (15)	0.78785 (2)	−0.00076 (6)	0.0239 (2)	0.5
O1	0.0963 (14)	0.87131 (13)	0.0035 (6)	0.073 (2)
O2	0.1397 (18)	0.8162 (2)	−0.2256 (5)	0.100 (4)
O3	0.6805 (14)	0.85641 (19)	−0.1043 (6)	0.082 (3)
O4	0.5112 (14)	0.75006 (18)	0.1933 (6)	0.072 (2)
O5	0.7465 (11)	0.83563 (18)	0.0979 (5)	0.066 (2)
O6	0.1609 (13)	0.8288 (2)	0.1983 (6)	0.081 (3)
C1	0.1892 (16)	0.8520 (2)	−0.0235 (7)	0.049 (2)
C2	0.2155 (19)	0.8180 (2)	−0.1636 (7)	0.061 (3)
C3	0.5412 (17)	0.84249 (19)	−0.0872 (7)	0.053 (2)
C4	0.4660 (15)	0.76641 (18)	0.1451 (6)	0.044 (2)
C5	0.6128 (14)	0.82003 (18)	0.0883 (6)	0.0412 (19)
C6	0.2509 (15)	0.8162 (2)	0.1493 (6)	0.046 (2)
C7	0.3620 (12)	0.74577 (16)	−0.0727 (5)	0.0324 (16)
H7	0.3937	0.7390	−0.1287	0.050*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Se1	0.0312 (5)	0.0293 (5)	0.0396 (6)	−0.0041 (4)	−0.0032 (5)	−0.0054 (4)
Se2	0.0233 (4)	0.0202 (4)	0.0282 (5)	−0.0021 (4)	−0.0028 (4)	−0.0017 (4)
Fe1	0.0424 (6)	0.0280 (5)	0.0308 (5)	−0.0075 (4)	−0.0071 (5)	0.0025 (4)
Fe2	0.0316 (5)	0.0319 (5)	0.0283 (5)	−0.0009 (4)	−0.0065 (5)	−0.0023 (4)
S1	0.0312 (5)	0.0293 (5)	0.0396 (6)	−0.0041 (4)	−0.0032 (5)	−0.0054 (4)
S2	0.0233 (4)	0.0202 (4)	0.0282 (5)	−0.0021 (4)	−0.0028 (4)	−0.0017 (4)
O1	0.090 (5)	0.031 (3)	0.097 (6)	0.011 (4)	0.001 (5)	−0.006 (4)
O2	0.137 (9)	0.116 (7)	0.046 (5)	−0.058 (7)	−0.046 (6)	0.023 (4)
O3	0.070 (6)	0.079 (5)	0.099 (7)	−0.044 (5)	−0.008 (5)	0.018 (5)
O4	0.085 (5)	0.065 (4)	0.066 (5)	0.000 (4)	−0.027 (5)	0.020 (4)
O5	0.053 (4)	0.085 (5)	0.061 (5)	−0.023 (4)	−0.009 (4)	−0.017 (4)
O6	0.067 (5)	0.111 (7)	0.064 (6)	0.017 (5)	0.003 (5)	−0.042 (5)
C1	0.055 (5)	0.038 (5)	0.053 (5)	−0.008 (4)	−0.015 (4)	0.006 (4)
C2	0.080 (8)	0.058 (6)	0.047 (6)	−0.036 (5)	−0.010 (6)	0.011 (4)
C3	0.064 (6)	0.037 (4)	0.057 (6)	−0.012 (4)	−0.007 (5)	0.005 (4)
C4	0.052 (5)	0.041 (4)	0.040 (5)	−0.006 (4)	−0.015 (4)	0.005 (3)
C5	0.040 (4)	0.044 (4)	0.040 (5)	0.000 (4)	0.000 (4)	−0.011 (3)
C6	0.044 (5)	0.050 (5)	0.045 (5)	−0.001 (4)	−0.008 (4)	−0.004 (4)
C7	0.035 (4)	0.032 (4)	0.030 (4)	0.000 (3)	0.002 (3)	−0.003 (3)

Geometric parameters (Å, º)

Se1/S1—C7	1.916 (7)	Fe2—C6	1.805 (10)
Se1/S1—Fe1	2.334 (2)	Fe2—C4	1.824 (8)
Se1/S1—Fe2	2.346 (2)	O1—C1	1.145 (13)
Se2/S2—C7^i	1.931 (8)	O2—C2	1.124 (13)
Se2/S2—Fe1	2.343 (1)	O3—C3	1.137 (12)
Se2/S2—Fe2	2.364 (1)	O4—C4	1.111 (11)
Fe1—C2	1.766 (11)	O5—C5	1.128 (11)
Fe1—C3	1.779 (10)	O6—C6	1.139 (12)
Fe1—C1	1.799 (11)	C7—C7^i	1.511 (16)
Fe1—Fe2	2.514 (2)	C7—H7	0.9800
Fe2—C5	1.797 (9)
C7—Se1/S1—Fe1	103.2 (2)	C5—Fe2—Se1/S1	90.0 (3)
C7—Se1/S1—Fe2	99.5 (2)	C6—Fe2—Se1/S1	164.2 (3)
Fe1—Se1/S1—Fe2	65.0 (1)	C4—Fe2—Se1/S1	102.4 (3)
C7^i—Se2/S2—Fe1	96.1 (2)	C5—Fe2—Se2/S2	146.2 (3)
C7^i—Se2/S2—Fe2	106.4 (2)	C6—Fe2—Se2/S2	88.7 (3)
Fe1—Se2/S2—Fe2	64.5 (1)	C4—Fe2—Se2/S2	115.2 (3)
C2—Fe1—C3	99.0 (5)	Se1/S1—Fe2—Se2/S2	81.8 (1)
C2—Fe1—C1	100.4 (5)	C5—Fe2—Fe1	90.8 (3)
C3—Fe1—C1	91.2 (5)	C6—Fe2—Fe1	107.0 (3)
C2—Fe1—Se1/S1	106.4 (4)	C4—Fe2—Fe1	157.8 (3)
C3—Fe1—Se1/S1	88.9 (3)	Se1/S1—Fe2—Fe1	57.3 (1)
C1—Fe1—Se1/S1	152.9 (3)	Se2/S2—Fe2—Fe1	57.3 (1)
C2—Fe1—Se2/S2	96.0 (3)	O1—C1—Fe1	176.7 (10)
C3—Fe1—Se2/S2	164.4 (3)	O2—C2—Fe1	177.3 (11)
C1—Fe1—Se2/S2	90.5 (3)	O3—C3—Fe1	178.0 (11)
Se1/S1—Fe1—Se2/S2	82.6 (1)	O4—C4—Fe2	174.8 (9)
C2—Fe1—Fe2	149.3 (3)	O5—C5—Fe2	178.7 (9)
C3—Fe1—Fe2	106.2 (3)	O6—C6—Fe2	179.1 (10)
C1—Fe1—Fe2	96.4 (3)	C7^i—C7—Se1/S1	113.2 (6)
Se1/S1—Fe1—Fe2	57.8 (1)	C7^i—C7—Se2/S2^i	110.9 (5)
Se2/S2—Fe1—Fe2	58.1 (1)	Se1/S1—C7—Se2/S2^i	113.0 (4)
C5—Fe2—C6	91.0 (4)	C7^i—C7—H7	106.4
C5—Fe2—C4	98.5 (4)	Se1/S1—C7—H7	106.4
C6—Fe2—C4	93.0 (4)	Se2/S2^i—C7—H7	106.4

Symmetry code: (i) −x+1/2, −y+3/2, z.