Di-tert-butyl­tin(IV)–hydroxide–iodide, ^tBu₂Sn(OH)I, the last missing member in the series of pure di-tert-butyl­tin(IV)–hydroxide–halides

The crystal structure of di-tert-butyl­hydroxido­iodido­tin(IV), [Sn(C₄H₉)₂I(OH)] or ^tBu₂Sn(OH)I, consists of dimeric, centrosymmetric mol­ecules exhibiting the typical structural features of diorganotin(IV)-hydroxide-halides, R₂Sn(OH)Hal. Two trigonal–bipyramidally coordinated tin(IV) atoms are bridged via two hydroxyl groups, resulting in a planar, four-membered {Sn—O}₂ ring of rhombic shape, with acute angles at tin, obtuse angles at oxygen and two different Sn—O distances depending whether the oxygen atom adopts an axial or equatorial position at the tin(IV) atom. In contrast to its fluorine, chlorine and bromine homologues, no hydrogen bonds between the OH group and the halide atom exist, confining the inter­molecular inter­actions to van der Waals forces.

1. Chemical context

During the hydrolysis of diorganotin(IV)-dihalides, R₂SnHal₂, to diorganotin(IV) oxides, R₂SnO, various inter­mediates are formed. The most prominent ones are the diorganotin-hydroxide-halides, R₂Sn(OH)Hal, the tetra­organo-dihalogenide-distannoxanes, (R₂SnHal)₂O, the tetra­organo-hydroxide-halide-distannoxanes, (R₂SnHal)O(R₂SnOH), and the tetra­organo-di­hydroxide-distannoxanes, (R₂SnOH)₂O. In solution as well as in the crystalline state, all these compounds are comprised of dimeric mol­ecules, and their compositions and structures result from a sequence of different hydrolysis, aggregation and condensation reactions.

In all three different classes of tetra­organo-distannoxanes, numerous compounds have been structurally characterized. All of therm exhibit a ladder-type arrangement of the Sn—O—Hal/OH framework [e.g. dihalogenides: R = Ph, Hal = Cl (Vollano et al., 1984), R = ⁱPr, Hal = Br (Beckmann et al., 2002a); hydroxide-halides: R = Et, Hal = Cl (Momeni et al., 2019), R = Ph, Hal = Br (Yap et al., 2010); di­hydroxides: R = neophyl (Reuter & Pawlak, 2000), R = tri­methyl­silylmethyl (Beckmann et al., 2002b)].

Pure hydroxide halides have been prepared and structurally characterized for ^tBu₂Sn(OH)Hal with Hal = F, Br (Puff et al., 1985), Hal = Cl (α-modification: Puff et al., 1985; β-modification: Di Nicola et al., 2011) and for R = p-tolyl and Hal = Br (Lo & Ng, 2009). Their structures are dominated by various –OH⋯Hal bridges between neighbouring mol­ecules, resulting in their chain-like arrangements. Hydroxide halides can be isolated when their hydroxyl groups are involved in hydrogen bonds to Brønstedt bases (BB). Such adducts of formula [R₂Sn(OH)Hal]·2BB have been described for R = Ph, Hal = Cl with BB = EtOH (Barba et al., 2007), and BB = quinoline (Anacona et al., 2003).

Here we present the mol­ecular and crystal structure of the last missing member in the series of pure di-tert-butyl­tin hydroxide halides where Hal = I. The analogous mol­ecule with DMSO as a hydrogen-bonded Brønsted base was formerly found as part of co-crystals with [(^tBu₂Sn)₃O(OH)₂I]I (Reuter & Wilberts, 2014).

2. Structural commentary

The asymmetric unit of the title compound comprises one ^tBu₂Sn(OH)I moiety that dimerizes to form a centrosymmetric mol­ecule (Fig. 1). As in all other hydroxide halides, dimerization occurs via the two hydroxyl groups that act as bridges between two trigonal–bipyramidally (tbpy) coordin­ated Sn^IV atoms.

Figure 1 Ball-and-stick model of the dimeric, centrosymmetric mol­ecule found in the crystal of ^tBu2Sn(OH)I, with atom numbering of the asymmetric unit. With the exception of the hydrogen atoms that are shown as spheres of arbitrary radius, all other atoms are drawn as displacement ellipsoids at the 40% probability level. The black dot labelled i indicates the position of the centre of symmetry.

The anisotropic displacement parameters as well as the small isotropic displacement parameters of the hydrogen atoms (see Refinement) indicate a negligibly small rotation of the tert-butyl groups as a whole and a small rotation of the methyl groups in particular, giving rise to very precise information on bond lengths and angles. The structural features of the tert-butyl groups are characterized by C—C bond lengths in the range 1.524 (3) to 1.533 (3) Å [mean value: 1.529 (3) Å], C—C—C angles in the range 109.5 (2) to 111.3 (2)° [mean value: 110.2 (7)°], Sn—C bond lengths between 2.187 (2) and 2.193 (2) Å [mean value: 2.190 (3) Å], and Sn—C—C angles of 107.8 (1)° to 109.6 (1)° [mean value: 108.8 (9)°]. All these values are more precise in comparison with those of the formerly determined di-tert-butyl­tin hydroxide halides (Puff et al., 1985; Di Nicola et al., 2011), especially as a result of low-temperature measurement and high data redundancy combined with multi-scan absorption correction, but are of the same accuracy and absolute value as those of the DMSO adduct [(^tBu₂Sn)₃O(OH)₂I]I [d(C—C) = 1.529 (4) Å, 〈(C—C—C) = 109.9 (4)°, d(Sn—C) = 2.193 (10), 〈(Sn—C—C) = 109.4 (7)°; Reuter & Wilberts, 2014]. These data are confirmed by a redetermination of the crystal structure of the α-modification of [^tBu₂Sn(OH)Cl)]₂ (Reuter, 2022) performed with similar experimental conditions as for the title compound and its co-crystallizate. In this context, Sn—C distances are of special inter­est as they belong to the longest ones observed in case of Sn in a trigonal–bipyramidal coordination. In the other hydroxide halides mentioned above, the following bond lengths have been found: d(Sn—C)_mean = 2.120 (8) Å for R = p-tolyl, Hal = Br; d(Sn—C)_mean = 2.121 (10)/2.117 (4) Å for R = Ph, Hal = Cl, BB = quinoline/EtOH.

Within the trigonal–bipyramidal coordination of the Sn^IV atom (Fig. 2), both tert-butyl groups are in equatorial (eq) positions in correspondence with the predictions of the VSEPR concept. The bond angle enclosed by the two tert-butyl groups of 126.81 (8)° is identical with the value [126.89 (9)°] in the co-crystal and lies in the range 122.0 (2) to 129.3 (1)° of C—Sn—C angles found in the other hydroxide-halides. The iodine atom adopts an axial (ax) position and one of the bridging hydroxyl groups is in an equatorial, the other in an axial position. As a result of dimerization via the hydroxyl groups, the axis of the trigonal bipyramid strongly deviates from linearity [I_ax—Sn—(OH)_ax = 151.94 (4)°]. In addition, the Sn—I distance of 2.8734 (2) Å is only marginally shorter than in the co-crystal [Sn—I = 2.8852 (2) Å], both being significantly longer than the sum (2.78 Å) of the covalent radii (Cordero et al., 2008) of tin (1.39 Å) and iodine (1.39 Å) and much longer than the mean Sn—I distance of 2.661 (2) (Reuter & Pawlak, 2001) in tin(IV) iodide, SnI₄, with tetra­hedrally coordinated tin.

Figure 2 Ball-and-stick model of the trigonal–bipyramidal coordination environment of the tin atom in the dimeric mol­ecule of ^tBu2Sn(OH)I with bond lengths (Å) and angles (°) characterizing the polyhedron axes. For clarity, methyl groups of the ^tBu ligands are stripped down to the carbon–carbon bonds drawn as shortened sticks. Atom O1′ is generated by symmetry code −x, −y + 1, −z + 1.

Because of the centrosymmetric nature of the dimer, the central four-membered {Sn—O}₂ ring is exactly planar. Its rhombic shape (Fig. 3) is characterized by acute angles [67.02 (6)°] at tin and obtuse ones [112.98 (6)°] at oxygen. Moreover, these rings exhibit two different Sn—O distances depending on the position (ax/eq) of the oxygen atom in the trigonal–bipyramidal coordination environment of tin(IV): Sn—(OH)_ax = 2.256 (1) Å versus Sn—(OH)_eq = 2.063 (1) Å. All these structural features are typical. For example, for the other four-membered {Sn—O}₂ rings of hydroxide halides with R = ^tBu, Hal = F, Cl, Br, the Sn—O—Sn angles range from 109.9 (2) to 112.5 (3)°, the O—Sn—O angles from 67.9 (3) to 70.1 (2)°, the Sn—(OH)_eq distances from 2.012 (5) to 2.048 (10) Å, and the Sn—(OH)_ax distances from 2.199 (5) to 2.25.7 (16) Å (Puff et al., 1985) .

Figure 3 Ball-and-stick model of the four-membered, centrosymmetric {Sn—O}2 ring in the dimeric mol­ecule of ^tBu2Sn(OH)I with bond lengths (Å) and angles (°) underlining its rhombic shape as the result of axially (ax) and equatorially (eq) bonded O atoms.

3. Supra­molecular features

While the hydroxyl groups of the [^tBu₂Sn(OH)I]₂ mol­ecules of the co-crystallizate (Reuter & Wilberts, 2014) are involved in OH⋯O hydrogen-bonding to DMSO mol­ecules, those of all other [^tBu₂Sn(OH)Hal]₂ mol­ecules develop inter­molecular O—H⋯Hal bonds resulting in a chain-like arrangement of the corresponding mol­ecules in the crystal. In contrast, there are no hydrogen bonds in the crystal structure of the title compound as the voluminous iodine atoms (Fig. 4) prevent significant inter­molecular OH⋯I inter­actions (Table 1). Hence, only van der Waals forces exist between the individual mol­ecules, resulting in a layer-like arrangement (Fig. 5) with the Sn—I bonds perpendicular to the layer plane. These layers expand perpendicular to the [101] direction (Fig. 6).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1⋯I1	0.96	2.93	3.3862 (14)	111

Figure 4 Space-filling model of the dimeric mol­ecule of ^tBu2Sn(OH)I showing the OH group wedged in between the iodine atom and the tert-butyl groups. Colour code: I = violet, H = white, C = grey, O = red, Sn = brass-coloured.

Figure 5 Space-filling model showing the layer-like arrangement of the dimeric [^tBuSn(OH)I]2 mol­ecules in the crystal structure. Top: top view; bottom: side view; colour code as in Fig. 4.

Figure 6 Stick-model showing the arrangement of layers with respect to the unit cell; colour code as in Fig. 4.

4. Synthesis and crystallization

Yellow block-like single crystals of the title compound were obtained after several years of storage in a sample of (^tBu₂Sn)₂I₂ originally prepared by the reaction of the cyclo­tetra­stannane (^tBu₂Sn)₄ with I₂ in toluene at elevated temperature in a molar ratio of 1:2. As other molar ratios and temperatures result in the formation of (^tBu₂Sn)₄I₂ or ^tBu₂SnI₂ (Farrar & Skinner, 1964; Adams & Dräger, 1985; Puff et al., 1989), it seems possible that the sample was contaminated with the latter one, which reacts over the long time of storage with atmospheric moisture to give the title compound.

5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. All hydrogen atoms were clearly identified in difference-Fourier syntheses. Those of the tert-butyl groups were refined with calculated positions (C—H = 0.98 Å) and a common U_iso(H) parameter for each of the methyl groups. The position of the H atom of the OH group was refined with a fixed O—H distance of 0.96 Å and the U_iso(H) parameter refined freely.

Table 2
Experimental details

Crystal data
Chemical formula	[Sn(C4H9)2I(OH)]
Mr	376.82
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	100
a, b, c (Å)	8.4903 (4), 10.8848 (5), 13.5107 (6)
β (°)	101.881 (2)
V (Å^3)	1221.85 (10)
Z	4
Radiation type	Mo Kα
μ (mm^−1)	4.58
Crystal size (mm)	0.24 × 0.12 × 0.09
Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015)
Tmin, Tmax	0.457, 0.715
No. of measured, independent and observed [I > 2σ(I)] reflections	48755, 2950, 2761
Rint	0.064
(sin θ/λ)max (Å^−1)	0.661
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.016, 0.037, 1.08
No. of reflections	2950
No. of parameters	114
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å^−3)	0.85, −0.49
Computer programs: APEX2 and SAINT (Bruker, 2009), SHELXS (Sheldrick, 2008), SHELXL (Sheldrick, 2015), DIAMOND (Brandenburg, 2006), Mercury (Macrae et al., 2020) and publCIF (Westrip, 2010).

Supporting information

Computing details

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS (Sheldrick, 2008); program(s) used to refine structure: SHELXL (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2006) and Mercury (Macrae et al., 2020); software used to prepare material for publication: publCIF (Westrip, 2010).

Di-tert-butylhydroxidoiodidotin(IV)

Crystal data

[Sn(C4H9)2I(OH)]	F(000) = 712
Mr = 376.82	Dx = 2.048 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 8.4903 (4) Å	Cell parameters from 9771 reflections
b = 10.8848 (5) Å	θ = 2.4–29.2°
c = 13.5107 (6) Å	µ = 4.58 mm^−1
β = 101.881 (2)°	T = 100 K
V = 1221.85 (10) Å^3	Block, yellow
Z = 4	0.24 × 0.12 × 0.09 mm

Data collection

Bruker APEXII CCD diffractometer	2761 reflections with I > 2σ(I)
φ and ω scans	Rint = 0.064
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θmax = 28.0°, θmin = 2.6°
Tmin = 0.457, Tmax = 0.715	h = −11→11
48755 measured reflections	k = −14→13
2950 independent reflections	l = −17→17

Refinement

Refinement on F^2	Hydrogen site location: mixed
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.016	w = 1/[σ^2(Fo^2) + (0.0075P)^2 + 1.3137P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.037	(Δ/σ)max = 0.003
S = 1.08	Δρmax = 0.85 e Å^−3
2950 reflections	Δρmin = −0.49 e Å^−3
114 parameters	Extinction correction: SHELXL-2014/7 (Sheldrick 2015, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.00139 (11)
Primary atom site location: structure-invariant direct methods

Special details

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

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

	x	y	z	Uiso*/Ueq
I1	0.31459 (2)	0.21150 (2)	0.53430 (2)	0.01973 (5)
Sn1	0.06240 (2)	0.37120 (2)	0.43364 (2)	0.01006 (5)
C21	0.1879 (2)	0.44568 (19)	0.32082 (15)	0.0137 (4)
C22	0.2375 (3)	0.3375 (2)	0.26155 (17)	0.0193 (5)
H22A	0.1409	0.2956	0.2247	0.032 (4)*
H22B	0.3027	0.2798	0.3086	0.032 (4)*
H22C	0.3004	0.3679	0.2135	0.032 (4)*
C23	0.3377 (3)	0.5141 (2)	0.37485 (17)	0.0190 (4)
H23A	0.3972	0.5445	0.3249	0.023 (4)*
H23B	0.4064	0.4582	0.4218	0.023 (4)*
H23C	0.3059	0.5835	0.4126	0.023 (4)*
C24	0.0749 (3)	0.5304 (2)	0.24902 (16)	0.0190 (4)
H24A	0.1273	0.5569	0.1944	0.027 (4)*
H24B	0.0495	0.6025	0.2863	0.027 (4)*
H24C	−0.0246	0.4863	0.2203	0.027 (4)*
C11	−0.1328 (3)	0.23567 (19)	0.40781 (16)	0.0153 (4)
C12	−0.2895 (3)	0.2973 (2)	0.35517 (19)	0.0233 (5)
H12A	−0.2754	0.3331	0.2910	0.029 (4)*
H12B	−0.3175	0.3623	0.3987	0.029 (4)*
H12C	−0.3759	0.2362	0.3421	0.029 (4)*
C13	−0.0867 (3)	0.1346 (2)	0.34001 (18)	0.0214 (5)
H13A	−0.0798	0.1697	0.2742	0.028 (4)*
H13B	−0.1687	0.0699	0.3304	0.028 (4)*
H13C	0.0178	0.0997	0.3721	0.028 (4)*
C14	−0.1500 (3)	0.1809 (2)	0.50925 (18)	0.0236 (5)
H14A	−0.2351	0.1185	0.4979	0.029 (4)*
H14B	−0.1781	0.2461	0.5526	0.029 (4)*
H14C	−0.0480	0.1431	0.5423	0.029 (4)*
O1	0.09927 (17)	0.46366 (13)	0.56977 (10)	0.0150 (3)
H1	0.1841	0.4272	0.6190	0.070 (12)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.02092 (9)	0.01756 (8)	0.01844 (8)	0.00750 (5)	−0.00125 (6)	0.00161 (5)
Sn1	0.01100 (8)	0.00881 (8)	0.01046 (7)	0.00010 (5)	0.00239 (5)	−0.00050 (5)
C21	0.0164 (10)	0.0130 (10)	0.0128 (9)	−0.0014 (8)	0.0051 (8)	−0.0012 (8)
C22	0.0235 (12)	0.0175 (11)	0.0188 (11)	−0.0001 (9)	0.0085 (9)	−0.0039 (9)
C23	0.0180 (11)	0.0196 (11)	0.0206 (11)	−0.0048 (9)	0.0067 (9)	−0.0020 (9)
C24	0.0236 (11)	0.0176 (11)	0.0158 (10)	0.0020 (9)	0.0040 (9)	0.0041 (8)
C11	0.0170 (10)	0.0131 (10)	0.0171 (10)	−0.0037 (8)	0.0064 (8)	−0.0040 (8)
C12	0.0153 (11)	0.0226 (12)	0.0308 (13)	−0.0029 (9)	0.0018 (9)	−0.0057 (10)
C13	0.0223 (12)	0.0173 (11)	0.0255 (12)	−0.0036 (9)	0.0070 (9)	−0.0083 (9)
C14	0.0295 (13)	0.0198 (12)	0.0250 (12)	−0.0054 (10)	0.0135 (10)	0.0012 (9)
O1	0.0166 (7)	0.0147 (7)	0.0126 (7)	0.0047 (6)	0.0004 (6)	−0.0021 (6)

Geometric parameters (Å, º)

I1—Sn1	2.8734 (2)	C24—H24C	0.9800
Sn1—O1	2.0631 (1)	C11—C12	1.528 (3)
Sn1—C21	2.187 (2)	C11—C14	1.529 (3)
Sn1—C11	2.193 (2)	C11—C13	1.533 (3)
Sn1—O1^i	2.2564 (1)	C12—H12A	0.9800
C21—C23	1.524 (3)	C12—H12B	0.9800
C21—C24	1.526 (3)	C12—H12C	0.9800
C21—C22	1.531 (3)	C13—H13A	0.9800
C22—H22A	0.9800	C13—H13B	0.9800
C22—H22B	0.9800	C13—H13C	0.9800
C22—H22C	0.9800	C14—H14A	0.9800
C23—H23A	0.9800	C14—H14B	0.9800
C23—H23B	0.9800	C14—H14C	0.9800
C23—H23C	0.9800	O1—Sn1^i	2.2563 (14)
C24—H24A	0.9800	O1—H1	0.9600
C24—H24B	0.9800
O1—Sn1—C21	115.73 (7)	C21—C24—H24C	109.5
O1—Sn1—C11	116.17 (7)	H24A—C24—H24C	109.5
C21—Sn1—C11	126.81 (8)	H24B—C24—H24C	109.5
O1—Sn1—O1^i	67.02 (6)	C12—C11—C14	110.71 (19)
C21—Sn1—O1^i	94.13 (7)	C12—C11—C13	109.99 (18)
C11—Sn1—O1^i	95.51 (7)	C14—C11—C13	109.84 (19)
O1—Sn1—I1	84.93 (4)	C12—C11—Sn1	109.60 (14)
C21—Sn1—I1	97.57 (5)	C14—C11—Sn1	109.16 (14)
C11—Sn1—I1	97.67 (6)	C13—C11—Sn1	107.47 (14)
O1^i—Sn1—I1	151.94 (4)	C11—C12—H12A	109.5
C23—C21—C24	111.25 (18)	C11—C12—H12B	109.5
C23—C21—C22	109.50 (17)	H12A—C12—H12B	109.5
C24—C21—C22	109.69 (17)	C11—C12—H12C	109.5
C23—C21—Sn1	109.00 (13)	H12A—C12—H12C	109.5
C24—C21—Sn1	109.55 (13)	H12B—C12—H12C	109.5
C22—C21—Sn1	107.78 (14)	C11—C13—H13A	109.5
C21—C22—H22A	109.5	C11—C13—H13B	109.5
C21—C22—H22B	109.5	H13A—C13—H13B	109.5
H22A—C22—H22B	109.5	C11—C13—H13C	109.5
C21—C22—H22C	109.5	H13A—C13—H13C	109.5
H22A—C22—H22C	109.5	H13B—C13—H13C	109.5
H22B—C22—H22C	109.5	C11—C14—H14A	109.5
C21—C23—H23A	109.5	C11—C14—H14B	109.5
C21—C23—H23B	109.5	H14A—C14—H14B	109.5
H23A—C23—H23B	109.5	C11—C14—H14C	109.5
C21—C23—H23C	109.5	H14A—C14—H14C	109.5
H23A—C23—H23C	109.5	H14B—C14—H14C	109.5
H23B—C23—H23C	109.5	Sn1—O1—Sn1^i	112.98 (6)
C21—C24—H24A	109.5	Sn1—O1—H1	111.7
C21—C24—H24B	109.5	Sn1^i—O1—H1	135.3
H24A—C24—H24B	109.5

Symmetry code: (i) −x, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···I1	0.96	2.93	3.3862 (14)	111