Bis([mu]-cyst­amine-[kappa]⁴N,S:S',N')­bis­[(2-amino­ethane­thiol­ato-[kappa]²N,S)­iridium(III)] tetrabromide dihydrate

In the complex cation of the title compound, [Ir₂(C₂H₆NS)₂(C₄H₁₂N₂S₂)₂]Br₄·2H₂O, which was obtained by rearrangement of [Re{Ir(aet)₃}₂]³⁺ (aet is 2-amino­ethane­thiol­ate) in an aqueous solution, two approximately octahedral fac(S)-[Ir(NH₂CH₂CH₂S)₃] units are linked by two coordinated di­sulfide bonds. The complex cation has a twofold axis, and the two non-bridging thiol­ate S atoms in the complex are located on opposite sides of the two di­sulfide bonds. Considering the absolute configurations of the two octahedral units ([Delta] and [Lambda]) and the four asymmetric di­sulfide S atoms (R and S), the complex consists of the [Delta]_RR[Delta]_RR and [Lambda]_SS[Lambda]_SS isomers, which combine to form the racemic compound.

S1. Comment

Previously, we have reported dinuclear Rh^III and Ir^III complexes containing a coordinated disulfide bond, [{M(aet)₂}₂(µ-cysta)]²⁺ (M = Rh^III and Ir^III, aet is 2-aminoethanethiolate and cysta is cystamine), formed? by oxidation of mononuclear complexes containing three thiolate S atoms, fac(S)-[M(aet)₃] (Konno et al., 1997; Miyashita et al., 1998). Furthermore, since thiolate S atoms can bridge two metal ions, construction of S-bridged polynuclear complexes using fac(S)-[M(aet)₃] units as building blocks has been investigated (Konno, 2004). For example, the reaction of fac(S)-[M(aet)₃] with metal ions, which prefer an octahedral geometry, selectively forms linear-type trinuclear complexes, [M'{M(aet)₃}₂]³⁺ (M' = Cr^III, Co^III, Rh^III etc.; Mahboob et al., 2004). Recently, we have synthesized the trinuclear complex involving the Re^III ion, [Re{Ir(aet)₃}₂]³⁺ (Mahboob et al., 2002). During the course of the recrystallizing processes, a novel dinuclear Ir^III complex containing two coordinated disulfide bonds was obtained. We report here the crystal structure of the title compound, [{Ir(aet)}₂(µ-cysta)₂]Br₄·2H₂O, (I), for comparison with those of the related complexes.

The asymmetric unit of (I) comprises one-half of a tetravalent dinuclear complex cation, two bromide anions and one water molecule. The complex cation consists of two approximately octahedral fac(S)-[Ir(NH₂CH₂CH₂S)₃] units, which are linked by two disulfide bonds (Fig. 1). There is a crystallographic twofold axis through the center of the S1—Siⁱ and S2—S2ⁱ bonds [symmetry code: (i) 1 − x, 1/2 − y, z]. The two non-bridging thiolate S atoms (S3 and S3ⁱ) are located on opposite sides of the two disulfide bonds. Considering the absolute configurations of the two octahedral units (Δ or Λ) and the four asymmetric disulfide S atoms (R or S), the present crystal of the double disulfide-bridged complex, [{Ir(aet)}₂(µ-cysta)₂]⁴⁺, is racemic, with Δ_RRΔ_RR and Λ_SSΛ_SS configurations. (The isomer shown in Fig. 1 is the Λ_SSΛ_SS isomer.) This configuration contrasts with the fact that the corresponding single disulfide-bridged complexes [{M(aet)₂}₂(µ-cysta)]²⁺ (M = Rh^III, Ir^III) are selectively obtained as the meso isomer, with Δ_RΛ_S configurations (Konno et al., 1997; Miyashita et al., 1998). On the other hand, a triple disulfide-bridged Ru^III complex (Albela et al., 1999) and a triple diselenide-bridged Rh^III complex (Konno et al., 2003) are obtained as the racemic isomer with Δ_RRRΔ_RRR and Λ_SSSΛ_SSS configurations.

As given in Table 1, the Ir—N(trans to disulfide) distances [mean 2.089 (12) Å] are shorter than the Ir—N(trans to thiolate) distances [2.148 (10) Å]. This behavior is in agreement with the case of [{Ir(aet)₂}₂(µ-cysta)]²⁺ (Konno et al., 1997; Miyashita et al., 1998), implying the trans influence of thiolate S atoms. The Ir—S(disulfide) distances [mean 2.304 (3) Å] are ca 0.04 Å shorter than the Ir—S(thiolate) distances [2.348 (3) Å]. The difference between the distances is smaller than that (0.08 Å) in [{Ir(aet)₂}₂(µ-cysta)]²⁺, probably because the S—S distances [mean 2.127 (6) Å] in (I) are slightly shorter than that [2.158 (3) Å] in [{Ir(aet)₂}₂(µ-cysta)]²⁺. In addition, these S—S distances are relatively long. For example, the S—S distance in [{IrCl(µ-SC₆H₂Me₂CH₂)(PPh₃)}₂(µ-ArSSAr)] (Ar is mesityl) is 2.109 (3) Å (Matsukawa et al., 2000).

Since the S(disulfide)—Ir—S(disulfide) angles [100.3 (1)°] are significantly larger than the ideal angle (90°), the N(trans to disulfide)—Ir—N(trans to disulfide) angles [86.9 (5)°] are smaller than the other N—Ir—N angles. On the other hand, the S(disulfide)—Ir—S(disulfide) angle in (I) is smaller than those in [M₂LI₂(MeCN)₂]²⁺ [mean 110.80 (4)° for M = Cu^II and mean 110.5 (2)° for M = Ni^II] with a macrocyclic ligand L (Fox et al., 2000). This means that the stereochemistry of the complex cation in (I) shows less strain, i.e., the Ir—S—S—Ir torsion angles are remarkably deviated from 0°. Interestingly, the two disulfide bonds have obviously distinguishable torsion angles (Table 1). Atom N1 of the aet moiety involving atom S1 occupies the position trans to the disulfide S atom, whereas atom N2 atom of the aet moiety involving atom S2 occupies the position trans to the thilate S atom. This difference leads to the difference in bond angles involving the disulfide bonds.

Since (I) could not be obtained by the direct oxidation of Δ/Λ-fac(S)-[Ir(aet)₃] or Δ_RΛ_S-[{Ir(aet)₂}₂(µ-cysta)]²⁺, it appears that the absolute configuration plays an important role in the formation of dinuclear complexes.

S2. Experimental

Orange powder of ΔΔ/ΛΛ-[Re{Ir(aet)₃}₂]I₃ (Mahboob et al., 2002) was dissolved in a small amount of water and subjected to an QAE-Sephadex A-25 column (Br⁻ form). The orange solution, which was eluted with water, was concentrated by a rotary evaporator and kept in a refrigerator after the addition of a few drops of a saturated NaBr aqueous solution. A small number of orange octahedral crystals appeared within several days.

S3. Refinement

H atoms bonded to C or N atoms were positioned geometrically and allowed to ride on their attached atoms [C—H = N—H = 0.95 Å and U_iso(H) = 1.2U_eq(C,N)]. H atoms of the water molecules were not included in the calculations.

Computing details

Data collection: WinAFC (Rigaku, 1999); cell refinement: WinAFC; data reduction: TEXSAN (Molecular Structure Corporation, 1999); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: TEXSAN; molecular graphics: reference?; software used to prepare material for publication: TEXSAN.

Figures

Fig. 1. A perspective drawing of the ΛSSΛSS isomer of [{Ir(aet)}2(µ-cysta)2]^4+, with the atom-numbering scheme, viewed down the crystallographic C2 axis. Displacement ellipsoids are shown at the 30% probability level and H atoms have been omitted for clarity. Atoms labelled with an asterisk (*) are at the symmetry position (1 − x, 1/2 − y, z).

(I)

Crystal data

[Ir2(C2H6NS)2(C4H12N2S2)2]Br4·2H2O	Dx = 2.597 Mg m^−3
Mr = 1196.90	Mo Kα radiation, λ = 0.7107 Å
Tetragonal, I41/a	Cell parameters from 22 reflections
a = 16.392 (3) Å	θ = 10.0–12.8°
c = 22.784 (6) Å	µ = 14.38 mm^−1
V = 6121 (2) Å^3	T = 296 K
Z = 8	Octahedron, red
F(000) = 4480	0.15 × 0.15 × 0.15 mm

Data collection

Rigaku AFC-7S diffractometer	Rint = 0.044
ω scans	θmax = 27.5°
Absorption correction: ψ scan (North et al., 1968)	h = −6→21
Tmin = 0.102, Tmax = 0.116	k = 0→21
4032 measured reflections	l = −8→29
3512 independent reflections	3 standard reflections every 150 reflections
2082 reflections with F^2 > 2σ(F^2)	intensity decay: 9.1%

Refinement

Refinement on F^2	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.047	w = 1/{σ^2(Fo^2) + [0.03(Max(Fo^2,0) + 2Fc^2]/3)^2}
wR(F^2) = 0.117	(Δ/σ)max = 0.001
S = 1.01	Δρmax = 1.72 e Å^−3
3512 reflections	Δρmin = −1.93 e Å^−3
145 parameters

Special details

Refinement. Refinement using reflections with F² > −10.0 σ(F²). The weighted R-factor (wR) and goodness of fit (S) are based on F². R-factor (gt) are based on F. The threshold expression of F² > 2.0 σ(F²) is used only for calculating R-factor (gt).

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

	x	y	z	Uiso*/Ueq
Ir1	0.64050 (3)	0.23658 (3)	0.04710 (2)	0.0195 (1)
Br1	0.6200 (1)	−0.0098 (1)	0.13903 (7)	0.0439 (5)
Br2	0.8636 (1)	0.0958 (1)	0.07177 (8)	0.0517 (5)
S1	0.5438 (2)	0.2020 (2)	0.1167 (1)	0.0231 (8)
S2	0.5623 (2)	0.2324 (2)	−0.0364 (1)	0.0242 (8)
S3	0.6298 (2)	0.3777 (2)	0.0629 (2)	0.0297 (9)
O1	0.954 (1)	0.1582 (9)	0.1988 (6)	0.087 (6)
N1	0.7227 (7)	0.2332 (7)	0.1167 (5)	0.026 (3)
N2	0.6542 (7)	0.1095 (6)	0.0262 (5)	0.026 (3)
N3	0.7399 (7)	0.2674 (7)	−0.0064 (6)	0.035 (3)
C1	0.6027 (9)	0.2335 (9)	0.1817 (6)	0.033 (4)
C2	0.6893 (10)	0.2033 (10)	0.1734 (6)	0.037 (4)
C3	0.5487 (8)	0.1215 (8)	−0.0481 (7)	0.034 (4)
C4	0.5784 (8)	0.0748 (8)	0.0030 (7)	0.031 (4)
C5	0.7254 (9)	0.4070 (8)	0.0292 (7)	0.038 (4)
C6	0.7406 (9)	0.3540 (9)	−0.0243 (8)	0.043 (5)
H1	0.7666	0.1985	0.1059	0.0312*
H2	0.7426	0.2870	0.1228	0.0312*
H3	0.6959	0.1037	−0.0024	0.0317*
H4	0.6691	0.0807	0.0608	0.0317*
H5	0.7888	0.2563	0.0146	0.0414*
H6	0.7380	0.2346	−0.0407	0.0414*
H7	0.6023	0.2912	0.1851	0.0395*
H8	0.5798	0.2100	0.2160	0.0395*
H9	0.6896	0.1453	0.1734	0.0441*
H10	0.7224	0.2228	0.2046	0.0441*
H11	0.4924	0.1102	−0.0538	0.0408*
H12	0.5784	0.1054	−0.0820	0.0408*
H13	0.5881	0.0200	−0.0086	0.0375*
H14	0.5380	0.0758	0.0329	0.0375*
H15	0.7227	0.4626	0.0176	0.0453*
H16	0.7685	0.3999	0.0565	0.0453*
H17	0.7922	0.3672	−0.0408	0.0521*
H18	0.6991	0.3632	−0.0526	0.0521*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ir1	0.0202 (2)	0.0182 (2)	0.0202 (2)	0.0007 (2)	−0.0018 (2)	0.0000 (2)
Br1	0.058 (1)	0.0411 (9)	0.0329 (8)	−0.0053 (8)	0.0064 (7)	0.0101 (7)
Br2	0.0457 (10)	0.061 (1)	0.049 (1)	0.0192 (9)	0.0036 (8)	0.0090 (9)
S1	0.027 (2)	0.022 (2)	0.020 (2)	0.004 (1)	0.001 (1)	0.001 (1)
S2	0.020 (2)	0.031 (2)	0.022 (2)	0.002 (1)	−0.001 (1)	0.000 (1)
S3	0.032 (2)	0.016 (2)	0.041 (2)	0.001 (1)	−0.003 (2)	0.001 (1)
O1	0.11 (1)	0.08 (1)	0.07 (1)	0.005 (9)	0.021 (10)	−0.014 (9)
N1	0.026 (6)	0.027 (6)	0.024 (6)	0.003 (5)	−0.009 (5)	0.002 (5)
N2	0.038 (7)	0.011 (5)	0.031 (6)	0.000 (5)	−0.007 (5)	−0.014 (5)
N3	0.025 (6)	0.035 (7)	0.043 (7)	0.000 (5)	0.005 (6)	0.003 (6)
C1	0.035 (8)	0.046 (9)	0.018 (6)	0.004 (7)	−0.004 (6)	−0.005 (6)
C2	0.046 (9)	0.049 (9)	0.016 (7)	0.015 (8)	−0.012 (6)	0.002 (6)
C3	0.026 (7)	0.033 (8)	0.043 (9)	−0.003 (6)	0.012 (7)	−0.005 (7)
C4	0.017 (6)	0.025 (7)	0.051 (9)	0.002 (5)	−0.004 (6)	−0.001 (7)
C5	0.037 (8)	0.021 (7)	0.06 (1)	−0.010 (6)	0.006 (7)	−0.001 (7)
C6	0.038 (9)	0.037 (9)	0.05 (1)	−0.006 (7)	0.011 (8)	0.028 (8)

Geometric parameters (Å, º)

Ir1—S1	2.313 (3)	N1—H2	0.950
Ir1—S2	2.295 (3)	N2—H3	0.950
Ir1—S3	2.348 (3)	N2—H4	0.950
Ir1—N1	2.082 (11)	N3—H5	0.950
Ir1—N2	2.148 (10)	N3—H6	0.950
Ir1—N3	2.096 (12)	C1—H7	0.950
S1—S1^i	2.130 (6)	C1—H8	0.950
S1—C1	1.840 (14)	C2—H9	0.950
S2—S2^i	2.124 (6)	C2—H10	0.950
S2—C3	1.852 (14)	C3—H11	0.950
S3—C5	1.809 (16)	C3—H12	0.950
N1—C2	1.48 (2)	C4—H13	0.950
N2—C4	1.46 (2)	C4—H14	0.950
N3—C6	1.48 (2)	C5—H15	0.950
C1—C2	1.52 (2)	C5—H16	0.949
C3—C4	1.48 (2)	C6—H17	0.950
C5—C6	1.52 (2)	C6—H18	0.949
N1—H1	0.950
Br1···N2	3.28 (1)	Br2···N2	3.59 (1)
Br1···N3^ii	3.28 (1)	O1···N3^iv	3.09 (2)
Br1···N2^ii	3.45 (1)	O1···O1^v	3.36 (3)
Br1···C3^ii	3.45 (1)	O1···C6^iv	3.38 (2)
Br1···C4	3.46 (2)	O1···C1^vi	3.38 (2)
Br2···N1	3.38 (1)	O1···N1^iv	3.54 (2)
Br2···O1^iii	3.39 (2)	O1···C5^iv	3.54 (2)
Br2···O1	3.41 (2)	C4···C4^vii	3.56 (3)
Br2···N1^iv	3.51 (1)
S1—Ir1—S2	100.3 (1)	C4—N2—H3	108.91
S1—Ir1—S3	94.9 (1)	C4—N2—H4	108.91
S1—Ir1—N1	85.1 (3)	H3—N2—H4	109.46
S1—Ir1—N2	89.2 (3)	Ir1—N3—H5	108.46
S1—Ir1—N3	172.0 (3)	Ir1—N3—H6	108.46
S2—Ir1—S3	96.6 (1)	C6—N3—H5	108.50
S2—Ir1—N1	172.8 (3)	C6—N3—H6	108.45
S2—Ir1—N2	81.1 (3)	H5—N3—H6	109.45
S2—Ir1—N3	87.7 (3)	S1—C1—H7	109.99
S3—Ir1—N1	87.6 (3)	S1—C1—H8	110.00
S3—Ir1—N2	175.7 (3)	C2—C1—H7	109.97
S3—Ir1—N3	84.8 (3)	C2—C1—H8	109.98
N1—Ir1—N2	94.3 (4)	H7—C1—H8	109.42
N1—Ir1—N3	86.9 (5)	N1—C2—H9	109.28
N2—Ir1—N3	91.4 (4)	N1—C2—H10	109.28
Ir1—S1—S1^i	106.3 (2)	C1—C2—H9	109.30
Ir1—S1—C1	97.1 (5)	C1—C2—H10	109.31
S1—S1^i—C1^i	98.4 (5)	H9—C2—H10	109.45
Ir1—S2—S2^i	121.96 (9)	S2—C3—H11	109.10
Ir1—S2—C3	102.5 (5)	S2—C3—H12	109.13
S2—S2^i—C3^i	98.6 (5)	C4—C3—H11	109.13
Ir1—S3—C5	97.6 (5)	C4—C3—H12	109.17
Ir1—N1—C2	115.6 (9)	H11—C3—H12	109.46
Ir1—N2—C4	111.6 (8)	N2—C4—H13	109.04
Ir1—N3—C6	113.5 (9)	N2—C4—H14	109.05
S1—C1—C2	107.5 (10)	C3—C4—H13	108.98
N1—C2—C1	110 (1)	C3—C4—H14	109.02
S2—C3—C4	110 (1)	H13—C4—H14	109.47
N2—C4—C3	111 (1)	S3—C5—H15	109.49
S3—C5—C6	109.4 (10)	S3—C5—H16	109.54
N3—C6—C5	108 (1)	C6—C5—H15	109.39
Ir1—N1—H1	107.91	C6—C5—H16	109.51
Ir1—N1—H2	107.90	H15—C5—H16	109.48
C2—N1—H1	107.93	N3—C6—H17	109.53
C2—N1—H2	107.91	N3—C6—H18	109.59
H1—N1—H2	109.45	C5—C6—H17	109.56
Ir1—N2—H3	108.94	C5—C6—H18	109.62
Ir1—N2—H4	108.96	H17—C6—H18	109.53
Ir1—S1—S1^i—Ir1^i	88.7 (2)	S2—S2^i—Ir1^i—N1^i	172 (2)
Ir1—S1—S1^i—C1^i	−171.3 (5)	S2—S2^i—Ir1^i—N2^i	122.0 (4)
Ir1—S1—C1—C2	−43 (1)	S2—S2^i—Ir1^i—N3^i	−146.2 (4)
Ir1—S2—S2^i—Ir1^i	−24.5 (4)	S2—S2^i—C3^i—C4^i	−116.0 (9)
Ir1—S2—S2^i—C3^i	86.1 (5)	S2—C3—C4—N2	−40 (1)
Ir1—S2—C3—C4	9.6 (10)	S3—Ir1—S1—C1	−68.0 (5)
Ir1—S3—C5—C6	37 (1)	S3—Ir1—S2—C3	−170.3 (4)
Ir1—N1—C2—C1	−37 (1)	S3—Ir1—N1—C2	101.7 (9)
Ir1—N2—C4—C3	55 (1)	S3—Ir1—N2—C4	−96 (4)
Ir1—N3—C6—C5	47 (1)	S3—Ir1—N3—C6	−18 (1)
S1—Ir1—S2—S2^i	34.5 (3)	S3—C5—C6—N3	−56 (1)
S1—Ir1—S2—C3	−74.1 (4)	N1—Ir1—S1—C1	19.2 (6)
S1—Ir1—S3—C5	161.8 (5)	N1—Ir1—S2—C3	64 (2)
S1—Ir1—N1—C2	6.6 (9)	N1—Ir1—S3—C5	76.9 (6)
S1—Ir1—N2—C4	62.9 (9)	N1—Ir1—N2—C4	147.9 (9)
S1—Ir1—N3—C6	−106 (2)	N1—Ir1—N3—C6	−106 (1)
S1—S1^i—Ir1^i—S2^i	−64.6 (2)	N2—Ir1—S1—C1	113.6 (6)
S1—S1^i—Ir1^i—S3^i	33.0 (2)	N2—Ir1—S2—C3	13.4 (5)
S1—S1^i—Ir1^i—N1^i	120.1 (3)	N2—Ir1—S3—C5	−38 (4)
S1—S1^i—Ir1^i—N2^i	−145.4 (3)	N2—Ir1—N1—C2	−82.2 (10)
S1—S1^i—Ir1^i—N3^i	120 (2)	N2—Ir1—N3—C6	159 (1)
S1—S1^i—C1^i—C2^i	−151.5 (10)	N3—Ir1—S1—C1	19 (2)
S1—C1—C2—N1	54 (1)	N3—Ir1—S2—C3	105.2 (5)
S2—Ir1—S1—C1	−165.6 (5)	N3—Ir1—S3—C5	−10.2 (6)
S2—Ir1—S3—C5	−97.2 (5)	N3—Ir1—N1—C2	−173.3 (10)
S2—Ir1—N1—C2	−132 (2)	N3—Ir1—N2—C4	−125.1 (10)
S2—Ir1—N2—C4	−37.7 (9)	C1—S1—S1^i—C1^i	−71.3 (10)
S2—Ir1—N3—C6	78 (1)	C3—S2—S2^i—C3^i	−163.3 (10)
S2—S2^i—Ir1^i—S3^i	−61.7 (3)

Symmetry codes: (i) −x+1, −y+1/2, z; (ii) −y+3/4, x−3/4, z+1/4; (iii) y+3/4, −x+5/4, −z+1/4; (iv) −y+5/4, x−3/4, −z+1/4; (v) −x+2, −y+1/2, z; (vi) −x+3/2, −y+1/2, −z+1/2; (vii) −x+1, −y, −z.