3,3'-Seleno­bis­(propionic acid)

In contrast to Se[CH₂C(O)OH]₂ versus S[CH₂C(O)OH]₂, the title compound, Se[CH₂CH₂C(O)OH]₂ or C₆H₁₀O₄Se, is structurally quite similar to its sulfur analogue. The mol­ecule has twofold symmetry. The C-Se-C bond angle is 96.48 (8)° and the Se-C bond lengths are 1.9610 (14) Å. The shortest Se...O intermolecular distance is 3.5410 (11) Å. The O...O distances in the carboxyl­ic acid dimers are 2.684 (2) Å. The temperature dependence of the IR spectrum suggests tautomerism in the solid state.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXTL (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

3,3'-Selenobis(propionic acid)

Crystal data

C6H10O4Se	? # Insert any comments here.
Mr = 225.10	Dx = 1.859 Mg m^−3
Orthorhombic, Pbcn	Melting point: 148° C K
Hall symbol: -P 2n 2ab	Mo Kα radiation, λ = 0.71073 Å
a = 8.5981 (3) Å	Cell parameters from 8192 reflections
b = 5.1355 (2) Å	θ = 2.2–33.2°
c = 18.2159 (7) Å	µ = 4.63 mm^−1
V = 804.33 (5) Å^3	T = 253 K
Z = 4	Flat prism, colourless
F(000) = 448	0.33 × 0.25 × 0.07 mm

Data collection

Bruker AXS SMART 2K CCD diffractometer	1481 independent reflections
Radiation source: normal focus sealed tube	1149 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
ω scans	θmax = 33.2°, θmin = 2.2°
Absorption correction: numerical (SHELXTL; Sheldrick 1997)	h = −13→13
Tmin = 0.296, Tmax = 0.724	k = −7→7
13334 measured reflections	l = −26→26

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)] = 0.023	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.061	w = 1/[σ^2(Fo^2) + (0.0307P)^2 + 0.1506P] where P = (Fo^2 + 2Fc^2)/3
S = 1.15	(Δ/σ)max < 0.001
1481 reflections	Δρmax = 0.43 e Å^−3
56 parameters	Δρmin = −0.54 e Å^−3
1 restraint	Extinction correction: SHELXTL (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0075 (9)

Special details

Experimental. ? #Insert any special details here.

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
Se	0.0000	0.18817 (4)	0.2500	0.02676 (8)
O1	−0.07447 (15)	0.8829 (2)	0.07928 (6)	0.0362 (3)
O2	0.13517 (14)	0.7398 (3)	0.01856 (7)	0.0379 (3)
H2	0.114 (3)	0.858 (4)	−0.0087 (12)	0.052 (6)*
C1	−0.06493 (16)	0.4425 (3)	0.17578 (8)	0.0258 (3)
H1A	−0.1455	0.3671	0.1452	0.039*
H1B	−0.1079	0.5948	0.1999	0.039*
C2	0.07177 (16)	0.5231 (3)	0.12815 (8)	0.0282 (3)
H2A	0.1548	0.5846	0.1597	0.042*
H2B	0.1099	0.3708	0.1023	0.042*
C3	0.03509 (17)	0.7322 (3)	0.07267 (9)	0.0247 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Se	0.03895 (13)	0.02022 (10)	0.02111 (11)	0.000	0.00105 (8)	0.000
O1	0.0414 (6)	0.0361 (6)	0.0310 (6)	0.0112 (5)	0.0049 (5)	0.0081 (5)
O2	0.0415 (6)	0.0388 (6)	0.0333 (6)	0.0074 (5)	0.0118 (5)	0.0142 (5)
C1	0.0266 (6)	0.0274 (7)	0.0234 (6)	0.0015 (6)	−0.0004 (5)	0.0031 (5)
C2	0.0265 (6)	0.0308 (7)	0.0273 (7)	0.0005 (6)	−0.0003 (5)	0.0075 (6)
C3	0.0269 (6)	0.0254 (6)	0.0218 (6)	−0.0026 (5)	−0.0011 (5)	0.0002 (5)

Geometric parameters (Å, º)

Se—C1^i	1.9610 (14)	C2—H2A	0.9700
Se—C1	1.9610 (14)	C2—H2B	0.9700
C1—C2	1.518 (2)	O1—C3	1.225 (2)
C1—H1A	0.9700	O2—C3	1.3091 (18)
C1—H1B	0.9700	O2—H2	0.804 (19)
C2—C3	1.508 (2)
C1^i—Se—C1	96.48 (8)	C3—C2—H2A	108.6
C3—O2—H2	109.9 (16)	C1—C2—H2A	108.6
C2—C1—Se	110.80 (10)	C3—C2—H2B	108.6
C2—C1—H1A	109.5	C1—C2—H2B	108.6
Se—C1—H1A	109.5	H2A—C2—H2B	107.6
C2—C1—H1B	109.5	O1—C3—O2	124.11 (15)
Se—C1—H1B	109.5	O1—C3—C2	123.02 (14)
H1A—C1—H1B	108.1	O2—C3—C2	112.84 (13)
C3—C2—C1	114.52 (12)
C1^i—Se—C1—C2	87.04 (10)	C1—C2—C3—O1	22.4 (2)
Se—C1—C2—C3	−176.08 (11)	C1—C2—C3—O2	−159.64 (14)

Symmetry code: (i) −x, y, −z+1/2.