(Triphenylarsine)iodinemonobromine: a charge-transfer adduct in which arsenic selectively bonds to iodine

The title molecule, (iodobromo)triphenylarsenic(III), [As(BrI)(C₆H₅)₃], has a dart shape, with the phenyl rings arranged in a propeller conformation [I-As-C-C 61.3 (4), 43.8 (4) and 54.1 (4)°]. There is no indication that the halogen atoms have mixed site occupancies. Packing forces displace the I atom away from one phenyl ring [I-As-C 117.3 (2)°] towards the other two [I-As-C 109.8 (2) and 108.3 (2)°] and produce an even more pronounced leaning of the terminal bromine [As-I-Br 174.78 (2)°].

S1. Comment

This work is a continuation of our investigation into adducts formed between group VA donors and the heavier halogens. Both Ph₃PI₂ [Godfrey et al., 1991; I—P—C—C 38 (1), 45 (1), 57 (1)°] and Ph₃PBr₂ [Bricklebank et al., 1992; Br—P—C—C 43.0 (9), 49.1 (9), 57.7 (8)°] have similar shapes to the title molecule, (I). However, at 2.5904 (8) Å, the As—I bond in (I) is shorter than any of the analogous bonds in the various polymorphs of Ph₃AsI₂ (Abbas et al., 1994; Beagley et al., 1988), which range from 2.613 (2) to 2.653 (2) Å. Interestingly, if a Lewis acid competes for the terminal iodine in Ph₃AsI₂, the As—I bond is shortened below the Ph₃AsIBr value, e.g. 2.485 (1) Å when GaI₃ is used as the Lewis acid (Baker et al., 1994). This suggests that the As—I bond is short in (I) because the Br—I bonding is weaker than the corresponding I—I interaction. In contrast to the disordered Ph₃PI_1.29Br_0.71 structure (Bricklebank et al., 1993), where P is attached to Br in 14 (2)% of the molecules, the structure of (I) contains no As—Br bonds.

S2. Experimental

Triphenylarsine (1.98 g, 7.25 mmol) was added to diethyl ether (ca 75 ml) under dry argon and a saturated ether solution of IBr (1.5 g, 7.25 mmol) was then added (Godfrey, 1993). A yellow solid precipitated immediately and was recrystallized from diethyl ether to give orange crystals suitable for X-ray analysis.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1994); cell refinement: CAD-4 Software; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELX97 (Sheldrick, 1997); program(s) used to refine structure: SHELX97; molecular graphics: ORTEPIII (Farrugia, 1997; Burnett & Johnson, 1996); software used to prepare material for publication: SHELX97.

Figures

Fig. 1. ORTEPIII (Farrugia, 1997; Burnett and Johnson, 1996) drawing of the structure of (I), showing the atom-numbering scheme and with 50% probability displacement ellispoids.

(iodobromo)triphenylarsenic

Crystal data

[As(BrI)(C6H5)3]	F(000) = 976
Mr = 513.03	Dx = 1.927 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 9.1198 (13) Å	Cell parameters from 25 reflections
b = 9.960 (2) Å	θ = 13.3–16.4°
c = 19.483 (3) Å	µ = 5.92 mm^−1
β = 92.176 (12)°	T = 203 K
V = 1768.4 (6) Å^3	Needle, orange
Z = 4	0.25 × 0.15 × 0.11 mm

Data collection

Nonius MACH3 diffractometer	2360 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.041
Graphite monochromator	θmax = 25.0°, θmin = 2.1°
2θ/ω scans	h = 0→10
Absorption correction: ψ-scan (North et al., 1968)	k = 0→11
Tmin = 0.386, Tmax = 0.521	l = −23→23
3270 measured reflections	3 standard reflections every 150 reflections
3065 independent reflections	intensity decay: 0.0%

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)] = 0.036	H-atom parameters constrained
wR(F^2) = 0.089	Calculated w = 1/[σ^2(Fo^2) + (0.0503P)^2 + 2.5099P] where P = (Fo^2 + 2Fc^2)/3
S = 1.02	(Δ/σ)max = 0.001
3065 reflections	Δρmax = 0.65 e Å^−3
191 parameters	Δρmin = −0.99 e Å^−3
0 restraints	Extinction correction: SHELX97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.00015 (19)

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.

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.

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

	x	y	z	Uiso*/Ueq
I1	0.25473 (4)	0.91923 (4)	0.664462 (18)	0.03120 (14)
Br1	0.09272 (6)	1.09119 (6)	0.75101 (3)	0.03675 (18)
As1	0.38469 (6)	0.74618 (6)	0.58831 (3)	0.02898 (17)
C1	0.2719 (5)	0.7190 (6)	0.5051 (3)	0.0295 (13)
C2	0.2100 (6)	0.5955 (6)	0.4894 (3)	0.0313 (13)
H2	0.2251	0.5227	0.5195	0.038*
C3	0.1261 (6)	0.5788 (7)	0.4295 (3)	0.0411 (15)
H3	0.0847	0.4945	0.4189	0.049*
C4	0.1029 (6)	0.6847 (7)	0.3854 (3)	0.0386 (15)
H4	0.0469	0.6726	0.3444	0.046*
C5	0.1619 (6)	0.8089 (7)	0.4013 (3)	0.0400 (15)
H5	0.1447	0.8819	0.3715	0.048*
C6	0.2476 (6)	0.8261 (6)	0.4621 (3)	0.0330 (13)
H6	0.2880	0.9106	0.4731	0.040*
C7	0.3923 (6)	0.5783 (6)	0.6358 (3)	0.0287 (12)
C8	0.2692 (6)	0.5341 (7)	0.6681 (3)	0.0394 (16)
H8	0.1856	0.5892	0.6693	0.047*
C9	0.2686 (6)	0.4104 (7)	0.6984 (3)	0.0405 (15)
H9	0.1837	0.3800	0.7195	0.049*
C10	0.3924 (7)	0.3293 (6)	0.6982 (3)	0.0360 (14)
H10	0.3916	0.2439	0.7188	0.043*
C11	0.5180 (7)	0.3760 (7)	0.6672 (3)	0.0397 (15)
H11	0.6027	0.3222	0.6674	0.048*
C12	0.5186 (6)	0.4999 (7)	0.6365 (3)	0.0366 (15)
H12	0.6038	0.5317	0.6162	0.044*
C13	0.5814 (5)	0.7866 (6)	0.5633 (3)	0.0298 (13)
C14	0.6242 (6)	0.7721 (6)	0.4968 (3)	0.0348 (14)
H14	0.5554	0.7487	0.4617	0.042*
C15	0.7699 (7)	0.7923 (7)	0.4825 (3)	0.0411 (16)
H15	0.7999	0.7864	0.4369	0.049*
C16	0.8710 (6)	0.8212 (7)	0.5346 (4)	0.0408 (16)
H16	0.9703	0.8323	0.5246	0.049*
C17	0.8283 (6)	0.8338 (7)	0.6006 (4)	0.0442 (17)
H17	0.8979	0.8553	0.6358	0.053*
C18	0.6838 (6)	0.8151 (7)	0.6160 (3)	0.0408 (16)
H18	0.6546	0.8215	0.6616	0.049*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.0184 (2)	0.0404 (2)	0.0344 (2)	−0.00318 (16)	−0.00319 (14)	−0.00032 (17)
Br1	0.0309 (3)	0.0378 (4)	0.0420 (3)	0.0022 (3)	0.0070 (2)	0.0009 (3)
As1	0.0137 (3)	0.0406 (4)	0.0325 (3)	−0.0029 (2)	−0.0011 (2)	−0.0015 (3)
C1	0.012 (3)	0.037 (4)	0.038 (3)	0.004 (2)	−0.004 (2)	0.001 (3)
C2	0.022 (3)	0.035 (3)	0.037 (3)	−0.001 (3)	0.002 (2)	−0.007 (3)
C3	0.024 (3)	0.050 (4)	0.049 (4)	−0.012 (3)	−0.005 (3)	−0.012 (3)
C4	0.019 (3)	0.058 (4)	0.039 (3)	0.001 (3)	−0.006 (2)	−0.011 (3)
C5	0.025 (3)	0.054 (4)	0.040 (3)	0.009 (3)	−0.007 (3)	−0.001 (3)
C6	0.021 (3)	0.033 (3)	0.045 (3)	0.001 (2)	−0.001 (3)	−0.005 (3)
C7	0.022 (3)	0.031 (3)	0.033 (3)	−0.002 (2)	−0.003 (2)	0.002 (3)
C8	0.014 (3)	0.060 (4)	0.044 (4)	−0.001 (3)	0.000 (2)	0.011 (3)
C9	0.024 (3)	0.053 (4)	0.043 (3)	−0.011 (3)	−0.004 (2)	0.007 (3)
C10	0.039 (4)	0.035 (4)	0.034 (3)	−0.003 (3)	−0.006 (3)	0.000 (3)
C11	0.034 (3)	0.049 (4)	0.035 (3)	0.009 (3)	−0.002 (3)	−0.005 (3)
C12	0.020 (3)	0.052 (4)	0.037 (3)	0.001 (3)	0.004 (2)	−0.003 (3)
C13	0.010 (2)	0.034 (3)	0.045 (3)	−0.007 (2)	−0.002 (2)	0.004 (3)
C14	0.020 (3)	0.043 (4)	0.041 (3)	−0.008 (3)	0.002 (2)	−0.007 (3)
C15	0.031 (3)	0.053 (4)	0.040 (4)	0.007 (3)	0.010 (3)	0.003 (3)
C16	0.017 (3)	0.038 (4)	0.067 (5)	0.004 (3)	0.000 (3)	0.012 (3)
C17	0.016 (3)	0.055 (4)	0.061 (4)	−0.005 (3)	−0.012 (3)	0.018 (4)
C18	0.030 (3)	0.057 (4)	0.035 (3)	−0.007 (3)	−0.006 (3)	0.008 (3)

Geometric parameters (Å, º)

I1—As1	2.5904 (8)	C7—C12	1.391 (8)
I1—Br1	2.8546 (8)	C8—C9	1.366 (9)
As1—C1	1.906 (5)	C9—C10	1.388 (9)
As1—C7	1.911 (6)	C10—C11	1.395 (9)
As1—C13	1.920 (5)	C11—C12	1.372 (9)
C1—C6	1.370 (8)	C13—C14	1.374 (8)
C1—C2	1.383 (8)	C13—C18	1.390 (8)
C2—C3	1.381 (8)	C14—C15	1.383 (8)
C3—C4	1.371 (9)	C15—C16	1.376 (9)
C4—C5	1.380 (9)	C16—C17	1.364 (9)
C5—C6	1.404 (8)	C17—C18	1.375 (8)
C7—C8	1.381 (8)
As1—I1—Br1	174.78 (2)	C8—C7—As1	119.0 (4)
C1—As1—C7	107.2 (2)	C12—C7—As1	120.7 (4)
C1—As1—C13	107.1 (2)	C9—C8—C7	120.1 (6)
C7—As1—C13	106.8 (2)	C8—C9—C10	120.5 (6)
C1—As1—I1	109.76 (17)	C9—C10—C11	119.2 (6)
C7—As1—I1	108.30 (17)	C12—C11—C10	120.4 (6)
C13—As1—I1	117.26 (18)	C11—C12—C7	119.5 (6)
C6—C1—C2	120.1 (5)	C14—C13—C18	120.7 (5)
C6—C1—As1	118.7 (4)	C14—C13—As1	121.2 (4)
C2—C1—As1	121.2 (4)	C18—C13—As1	117.6 (4)
C3—C2—C1	120.2 (6)	C13—C14—C15	119.0 (6)
C4—C3—C2	120.3 (6)	C16—C15—C14	120.2 (6)
C3—C4—C5	119.9 (6)	C17—C16—C15	120.5 (6)
C4—C5—C6	119.9 (6)	C16—C17—C18	120.2 (6)
C1—C6—C5	119.5 (6)	C17—C18—C13	119.3 (6)
C8—C7—C12	120.3 (6)