(2-Carbo­methoxy­ethyl)­tri­iodo­tin at 120 K

The title compound, [SnI₃(C₄H₇O₂)], is a member of the comparatively well known estertin family of compounds in which the carbonyl O of the 2-carbo­alkoxy­ethyl fragment bonds to Sn, augmenting its coordination and creating a five-membered chelate ring. The present case, where, as is often the case, Sn has trigonal bipyramidal coordination, is notable for the presence in the asymmetric unit of two distinct mol­ecules markedly different in terms of the trans-axial Sn-O and Sn-I distances, 2.459 (8) versus 2.631 (8) and 2.7601 (10) versus 2.7188 (9) Å, respectively, and much greater pucker of the chelate ring associated with the longer Sn-O bond.

Key indicators

• Single-crystal X-ray study
• T = 120 K
• Mean [sigma](C-C) = 0.016 Å
• R factor = 0.060
• wR factor = 0.168
• Data-to-parameter ratio = 27.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



ABSTM_02  Alert C The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
          Tmin and Tmax reported:      0.269     0.505
          Tmin and Tmax expected:      0.203     0.453
          RR =      1.189
          Please check that your absorption correction is appropriate.

REFLT_03
         From the CIF: _diffrn_reflns_theta_max           27.50
         From the CIF: _reflns_number_total               5138
         TEST2: Reflns within _diffrn_reflns_theta_max
         Count of symmetry unique reflns         5464
         Completeness (_total/calc)             94.03%
          Alert C: < 95% complete

RINTA_01  Alert C The value of Rint is greater than 0.10
          Rint given   0.107

PLAT_710  Alert C Delete 1-2-3 or 2-3-4 (CIF) Linear Torsion Angle #     27
                   I1B -SN1B-O1B -C3B    76.00  5.00   1.555   1.555   1.555   1.555

General Notes



ABSTM_02  When printed, the submitted absorption T values will be replaced
          by the scaled T values. Since the ratio of scaled T's is
          identical to the ratio of reported T values, the scaling does
          not imply a change to the absorption corrections used in the
          study.
          Ratio of Tmax expected/reported      0.897
          Tmax scaled      0.453 Tmin scaled      0.241


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 4 Alert Level C = Please check

---

S1. Comment

At this time, the Cambridge Structural Database (CSD; Allen & Kennard, 1993) contains entries for approximately 30 estertin compounds. Two of these, namely (2-carbomethoxyethyl)trichlorotin (CMESNC; Harrison et al., 1979), (II), and (2-carboisopropoxyethyl)trichlorotin (FAYSUT; Howie et al., 1986), (III), are particularly relevant to the discussion of the title compound, (I).

Unlike (II) and (III), in (I), the asymmetric unit contains not one but two molecules. Both molecules in (I) are labelled in an identical manner largely compatible with that used for the molecules of (II) and (III) (Fig. 1), but distinguished by suffix A or B. Bond distances and angles in molecules A and B of (I) involving Sn are given in Table 1. Here it is clear, as exemplified in Fig. 1, that Sn is five-coordinate in the form of a distorted trigonal bipyramid with axial O1 and I1 and equatorial I2, I3 and C1 in both molecules. Particularly significant are the longer Sn1—I1 and shorter Sn1—O1 trans-axial bonds in molecule A compared with bonds of the same type in molecule B. Aside from the inevitable differences between Sn—I, Sn—C and Sn—O distances the most obvious distortion of the coordination of Sn lies in the O1—Sn1—C1 chelate bite angle but this distortion, while still very obvious, is less for molecule A than it is for molecule B. Indeed, obviously excepting the trans-axial angle O1—Sn1—I1, almost all of the angles at Sn are closer to the ideal values of 120 or 90° in molecule A than they are in molecule B.

Table 2 compares the bond and torsion angles within the five-membered chelate rings of molecules A and B of (I) and the molecules of (II) and (III). While there is comparatively little variation in the bond angles the torsion angles clearly demonstrate significant puckering in the chelate ring of molecule B of (I) [pucker parameters (Cremer & Pople, 1975) Q₂ = 0.498 (10) Å and ϕ₂ = 150.8 (13)°], much less in the molecule of (II) [Q₂ 0.097 Å and ϕ₂ = 138.5°] and closest description envelope with C1 at the point of the flap in both of these and virtually none in molecule A of (I) and the molecule of (III) [Q₂ and ϕ₂ found indeterminate by PLATON for these last two]. The r.m.s. deviations for the fitted atoms for each of the Sn1/C1/C2/C3/O1 planes [0.216, 0.043, 0.025 and 0.018 Å for molecule B of (I), (II), molecule A of (I) and for (III), respectively] confirm the decrease in puckering or increase in planarity in the order given.

Another major difference between molecules A and B of (I) is that I1A of molecule A acts as acceptor for the two C—H···I weak intermolecular hydrogen bonds given in Table 3. There is no corresponding interaction in the case of molecule B. These contacts interconnect the molecules of both types to form zigzag chains propagated in the direction of c as shown in Fig. 2. As indicated in Fig. 3, the chains lie face-to-face and related one to the next by cell translation in the direction of a, forming layers centred on the c-glides of the space group P2₁/c at y = 1/4 and 3/4. Adjacent layers are related by crystallographic centres of symmetry.

It is suggested, therefore, that the comparatively short, relative to molecule B, Sn1A–O1A distance and the concomitant relative planarity of the chelate ring in molecule A is probably due to lengthening and weakening of the Sn1A—I1A bond due to the role of I1A as hydrogen bond, weak though the bonds are, acceptor.

S2. Experimental

Compound (I) was obtained by halide exchange of the corresponding chloride (II). Thus, a solution of (II) (2 mmol) and NaI (ca 20 mmol) in acetone (40 ml) was stirred at room temperature for 1 h. The reaction mixture was then rotary evaporated and the solid residue extracted with chloroform (2 × 30 ml). The combined extracts were rotary evaporated once more and the solid product recrystallized from EtOH to yield crystals of (I) (m.p. 337–339 K) suitable for analysis.

S3. Refinement

In the final stages, H atoms were introduced in calculated positions with C—H distances of 0.98 and 0.99 Å for methyl and methylene H, respectively, and refined with a riding model with U_iso 1.5 and 1.2U_eq again, respectively. The final difference map showed a number of large peaks as high as, e.g. 3.16 e Å^-3 0.87 Å from I3A, but all in the vicinity of Sn or I and attributable to ripples.

Computing details

Data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 1990).

Figures

	Fig. 1. The atomic arrangement in both molecules of (I). Non-H atoms are shown as 50% ellipsoids, H atoms as small circles and the Sn1—O1 bond as a dashed line. The example shown is molecule A.
	Fig. 2. A portion of a zigzag chain of molecules of (I). Selected atoms are labelled in a generic manner and dashed lines represent either intermolecular C—H···I hydrogen bonds, whose H atoms are the only H shown, or intramolecular Sn—O bonds. The representation is otherwise as for Fig. 1.
	Fig. 3. The unit cell of (I). The cell outline is shown but the representation, lacking only the Sn—O bonds, is otherwise the same as Fig. 2.

(2-Carbomethoxyethyl)triiodotin at 120 K

Crystal data

[SnI3(C4H7O2)]	F(000) = 2048
Mr = 586.49	Dx = 3.277 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.3950 (1) Å	Cell parameters from 14043 reflections
b = 25.8407 (4) Å	θ = 2.9–27.5°
c = 12.4431 (2) Å	µ = 9.90 mm^−1
β = 90.4600 (8)°	T = 120 K
V = 2377.70 (6) Å^3	Block, yellow
Z = 8	0.18 × 0.14 × 0.08 mm

Data collection

Enraf-Nonius KappaCCD area-detector diffractometer	5138 independent reflections
Radiation source: Enraf-Nonius FR591 rotating anode	4645 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.107
Detector resolution: 9.091 pixels mm^-1	θmax = 27.5°, θmin = 3.2°
ϕ and ω scans to fill the Ewald sphere	h = −9→9
Absorption correction: multi-scan (SORTAV; Blessing, 1995, 1997)	k = −33→33
Tmin = 0.269, Tmax = 0.505	l = −16→16
20814 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.060	H-atom parameters constrained
wR(F^2) = 0.168	w = 1/[σ^2(Fo^2) + (0.0892P)^2 + 21.9385P] where P = (Fo^2 + 2Fc^2)/3
S = 1.14	(Δ/σ)max = 0.001
5138 reflections	Δρmax = 3.16 e Å^−3
184 parameters	Δρmin = −2.71 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.00204 (18)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

0.3242(0.0297) x + 18.3176(0.0831) y - 8.7638(0.0414) z = 3.7257(0.0949)

* -0.0151 (0.0046) Sn1A * 0.0081 (0.0081) C1A * 0.0117 (0.0096) C2A * -0.0385 (0.0082) C3A * 0.0338 (0.0059) O1A -0.0300 (0.0131) I1A -2.3806 (0.0087) I2A 2.1109 (0.0104) I3A -0.1512 (0.0146) O2A -0.1757 (0.0213) C4A

Rms deviation of fitted atoms = 0.0247

1.0427(0.0309) x + 13.7880(0.0973) y + 10.3621(0.0347) z = 11.3573(0.0163)

Angle to previous plane (with approximate e.s.d.) = 78.31 (0.28)

* 0.1758 (0.0047) Sn1B * -0.3236 (0.0079) C1B * 0.2835 (0.0084) C2B * -0.0064 (0.0080) C3B * -0.1294 (0.0061) O1B 0.3987 (0.0131) I1B 2.7021 (0.0066) I2B -1.5704 (0.0127) I3B -0.1057 (0.0147) O2B -0.4687 (0.0204) C4B

Rms deviation of fitted atoms = 0.2158

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Anisotropic displacement parameters refined for all non-H atoms. H atoms in calculated positions and refined with a riding model.

Intensity data 93.6% complete out to 50 °. 2-theta.

Max Delta(rho) 3.16 e-Ang**-3 0.87 from I3A and largest of ca 24 large features (down to 1.57 e-Ang**-3 approx. 1 A ng distant from Sn or I) and attributed to ripple.

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

	x	y	z	Uiso*/Ueq
Sn1A	0.33608 (9)	0.63670 (2)	0.91984 (5)	0.0201 (2)
I1A	0.13667 (11)	0.70147 (3)	1.04953 (6)	0.0354 (2)
I2A	0.21626 (10)	0.54496 (2)	0.99356 (7)	0.0321 (2)
I3A	0.19303 (10)	0.66415 (3)	0.72933 (6)	0.0300 (2)
C1A	0.6052 (14)	0.6572 (4)	0.9700 (9)	0.027 (2)
H1A1	0.6236	0.6946	0.9572	0.032*
H1A2	0.6174	0.6510	1.0482	0.032*
C2A	0.7492 (16)	0.6277 (6)	0.9133 (11)	0.041 (3)
H2A1	0.8272	0.6528	0.8754	0.049*
H2A2	0.8253	0.6102	0.9681	0.049*
C3A	0.6881 (14)	0.5881 (4)	0.8339 (9)	0.026 (2)
O1A	0.5295 (10)	0.5820 (3)	0.8070 (7)	0.0305 (17)
O2A	0.8200 (12)	0.5605 (3)	0.7940 (7)	0.038 (2)
C4A	0.7682 (19)	0.5219 (5)	0.7141 (11)	0.042 (3)
H4A1	0.6549	0.5053	0.7356	0.064*
H4A2	0.8635	0.4957	0.7089	0.064*
H4A3	0.7514	0.5387	0.6441	0.064*
Sn1B	0.14771 (10)	0.34482 (2)	0.63933 (6)	0.0235 (2)
I1B	0.33283 (13)	0.26872 (3)	0.74346 (7)	0.0382 (2)
I2B	0.23598 (11)	0.42592 (2)	0.76633 (6)	0.0288 (2)
I3B	0.32701 (12)	0.34466 (3)	0.45298 (6)	0.0374 (2)
C1B	−0.1341 (17)	0.3264 (4)	0.6440 (10)	0.033 (3)
H1B1	−0.1676	0.3065	0.5788	0.040*
H1B2	−0.1581	0.3043	0.7074	0.040*
C2B	−0.2493 (15)	0.3747 (4)	0.6500 (11)	0.034 (3)
H2B1	−0.3781	0.3654	0.6391	0.040*
H2B2	−0.2362	0.3906	0.7220	0.040*
C3B	−0.1932 (16)	0.4125 (4)	0.5660 (9)	0.029 (2)
O1B	−0.0368 (10)	0.4159 (3)	0.5339 (6)	0.0268 (16)
O2B	−0.3236 (11)	0.4425 (3)	0.5296 (7)	0.0351 (19)
C4B	−0.2761 (17)	0.4781 (5)	0.4425 (11)	0.035 (3)
H4B1	−0.1802	0.5015	0.4671	0.053*
H4B2	−0.3829	0.4983	0.4215	0.053*
H4B3	−0.2335	0.4582	0.3806	0.053*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn1A	0.0209 (4)	0.0185 (3)	0.0209 (4)	−0.0019 (2)	−0.0055 (3)	−0.0008 (2)
I1A	0.0444 (5)	0.0292 (4)	0.0326 (5)	0.0032 (3)	0.0004 (3)	−0.0091 (3)
I2A	0.0331 (4)	0.0207 (3)	0.0427 (5)	−0.0037 (3)	−0.0012 (3)	0.0059 (3)
I3A	0.0313 (4)	0.0347 (4)	0.0238 (4)	0.0063 (3)	−0.0080 (3)	0.0022 (3)
C1A	0.018 (5)	0.035 (5)	0.027 (6)	−0.010 (4)	−0.005 (4)	−0.007 (4)
C2A	0.015 (6)	0.067 (8)	0.041 (7)	0.009 (5)	0.000 (5)	−0.018 (6)
C3A	0.016 (5)	0.028 (5)	0.035 (6)	0.003 (4)	−0.006 (4)	0.000 (4)
O1A	0.021 (4)	0.034 (4)	0.037 (5)	0.006 (3)	−0.006 (3)	−0.008 (3)
O2A	0.039 (5)	0.042 (4)	0.032 (5)	0.014 (4)	−0.001 (4)	0.004 (4)
C4A	0.043 (8)	0.044 (7)	0.040 (7)	0.013 (6)	−0.003 (6)	−0.008 (6)
Sn1B	0.0303 (4)	0.0184 (3)	0.0218 (4)	0.0037 (3)	−0.0058 (3)	−0.0001 (2)
I1B	0.0562 (6)	0.0242 (4)	0.0341 (5)	0.0138 (3)	−0.0127 (4)	0.0007 (3)
I2B	0.0404 (5)	0.0204 (3)	0.0254 (4)	0.0021 (3)	−0.0075 (3)	−0.0016 (2)
I3B	0.0484 (5)	0.0399 (4)	0.0240 (4)	0.0103 (3)	−0.0003 (3)	−0.0033 (3)
C1B	0.043 (7)	0.021 (5)	0.036 (7)	−0.011 (4)	−0.006 (5)	−0.001 (4)
C2B	0.015 (5)	0.036 (6)	0.050 (8)	−0.008 (4)	−0.011 (5)	0.015 (5)
C3B	0.031 (6)	0.021 (4)	0.034 (6)	0.003 (4)	−0.006 (5)	0.005 (4)
O1B	0.022 (4)	0.028 (3)	0.031 (4)	−0.001 (3)	0.004 (3)	0.001 (3)
O2B	0.024 (4)	0.035 (4)	0.046 (5)	0.004 (3)	−0.001 (4)	0.017 (4)
C4B	0.032 (7)	0.034 (6)	0.041 (7)	0.001 (5)	−0.003 (5)	0.015 (5)

Geometric parameters (Å, º)

Sn1A—C1A	2.147 (10)	Sn1B—C1B	2.139 (12)
Sn1A—O1A	2.459 (8)	Sn1B—O1B	2.631 (8)
Sn1A—I3A	2.6835 (9)	Sn1B—I3B	2.6803 (11)
Sn1A—I2A	2.6944 (9)	Sn1B—I2B	2.7016 (9)
Sn1A—I1A	2.7601 (10)	Sn1B—I1B	2.7188 (9)
C1A—C2A	1.492 (16)	C1B—C2B	1.513 (16)
C1A—H1A1	0.9900	C1B—H1B1	0.9900
C1A—H1A2	0.9900	C1B—H1B2	0.9900
C2A—C3A	1.491 (16)	C2B—C3B	1.493 (16)
C2A—H2A1	0.9900	C2B—H2B1	0.9900
C2A—H2A2	0.9900	C2B—H2B2	0.9900
C3A—O1A	1.227 (13)	C3B—O1B	1.229 (14)
C3A—O2A	1.308 (14)	C3B—O2B	1.316 (13)
O2A—C4A	1.458 (16)	O2B—C4B	1.465 (14)
C4A—H4A1	0.9800	C4B—H4B1	0.9800
C4A—H4A2	0.9800	C4B—H4B2	0.9800
C4A—H4A3	0.9800	C4B—H4B3	0.9800
C1A—Sn1A—O1A	76.5 (3)	C1B—Sn1B—O1B	70.6 (3)
C1A—Sn1A—I3A	123.3 (3)	C1B—Sn1B—I3B	120.8 (3)
O1A—Sn1A—I3A	82.80 (19)	O1B—Sn1B—I3B	80.09 (17)
C1A—Sn1A—I2A	115.1 (3)	C1B—Sn1B—I2B	112.8 (3)
O1A—Sn1A—I2A	83.3 (2)	O1B—Sn1B—I2B	82.66 (17)
I3A—Sn1A—I2A	113.89 (3)	I3B—Sn1B—I2B	112.85 (4)
C1A—Sn1A—I1A	100.3 (3)	C1B—Sn1B—I1B	108.2 (3)
O1A—Sn1A—I1A	176.67 (19)	O1B—Sn1B—I1B	177.89 (17)
I3A—Sn1A—I1A	98.48 (3)	I3B—Sn1B—I1B	99.24 (4)
I2A—Sn1A—I1A	98.96 (3)	I2B—Sn1B—I1B	99.43 (3)
C2A—C1A—Sn1A	113.6 (7)	C2B—C1B—Sn1B	111.5 (7)
C2A—C1A—H1A1	108.8	C2B—C1B—H1B1	109.3
Sn1A—C1A—H1A1	108.8	Sn1B—C1B—H1B1	109.3
C2A—C1A—H1A2	108.8	C2B—C1B—H1B2	109.3
Sn1A—C1A—H1A2	108.8	Sn1B—C1B—H1B2	109.3
H1A1—C1A—H1A2	107.7	H1B1—C1B—H1B2	108.0
C3A—C2A—C1A	116.8 (10)	C3B—C2B—C1B	110.2 (10)
C3A—C2A—H2A1	108.1	C3B—C2B—H2B1	109.6
C1A—C2A—H2A1	108.1	C1B—C2B—H2B1	109.6
C3A—C2A—H2A2	108.1	C3B—C2B—H2B2	109.6
C1A—C2A—H2A2	108.1	C1B—C2B—H2B2	109.6
H2A1—C2A—H2A2	107.3	H2B1—C2B—H2B2	108.1
O1A—C3A—O2A	122.8 (10)	O1B—C3B—O2B	122.3 (10)
O1A—C3A—C2A	123.5 (10)	O1B—C3B—C2B	122.8 (10)
O2A—C3A—C2A	113.7 (9)	O2B—C3B—C2B	114.9 (10)
C3A—O1A—Sn1A	109.3 (7)	C3B—O1B—Sn1B	105.9 (6)
C3A—O2A—C4A	116.0 (10)	C3B—O2B—C4B	116.4 (9)
O2A—C4A—H4A1	109.5	O2B—C4B—H4B1	109.5
O2A—C4A—H4A2	109.5	O2B—C4B—H4B2	109.5
H4A1—C4A—H4A2	109.5	H4B1—C4B—H4B2	109.5
O2A—C4A—H4A3	109.5	O2B—C4B—H4B3	109.5
H4A1—C4A—H4A3	109.5	H4B1—C4B—H4B3	109.5
H4A2—C4A—H4A3	109.5	H4B2—C4B—H4B3	109.5
O1A—Sn1A—C1A—C2A	−1.1 (9)	I3B—Sn1B—C1B—C2B	−100.0 (8)
I3A—Sn1A—C1A—C2A	−72.9 (10)	I2B—Sn1B—C1B—C2B	37.9 (9)
I2A—Sn1A—C1A—C2A	74.6 (10)	I1B—Sn1B—C1B—C2B	146.9 (8)
I1A—Sn1A—C1A—C2A	179.7 (9)	Sn1B—C1B—C2B—C3B	49.3 (11)
Sn1A—C1A—C2A—C3A	−1.6 (16)	C1B—C2B—C3B—O1B	−30.9 (16)
C1A—C2A—C3A—O1A	6 (2)	C1B—C2B—C3B—O2B	149.8 (10)
C1A—C2A—C3A—O2A	−174.3 (11)	O2B—C3B—O1B—Sn1B	−179.8 (9)
O2A—C3A—O1A—Sn1A	173.9 (9)	C2B—C3B—O1B—Sn1B	1.0 (13)
C2A—C3A—O1A—Sn1A	−7.0 (14)	C1B—Sn1B—O1B—C3B	19.9 (8)
C1A—Sn1A—O1A—C3A	4.3 (8)	I3B—Sn1B—O1B—C3B	147.7 (7)
I3A—Sn1A—O1A—C3A	131.2 (7)	I2B—Sn1B—O1B—C3B	−97.4 (7)
I2A—Sn1A—O1A—C3A	−113.6 (7)	I1B—Sn1B—O1B—C3B	76 (5)
O1A—C3A—O2A—C4A	0.5 (16)	O1B—C3B—O2B—C4B	4.3 (17)
C2A—C3A—O2A—C4A	−178.7 (11)	C2B—C3B—O2B—C4B	−176.5 (10)
O1B—Sn1B—C1B—C2B	−35.0 (8)