Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801016099/cv6062sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536801016099/cv6062Isup2.hkl |
CCDC reference: 175969
Key indicators
- Single-crystal X-ray study
- T = 293 K
- Mean (C-C) = 0.005 Å
- R factor = 0.053
- wR factor = 0.137
- Data-to-parameter ratio = 16.5
checkCIF results
No syntax errors found ADDSYM reports no extra symmetry
Colourless single crystals of (I) were grown from a saturated aqueous solution containing DL-valine and ZnCl2 in stoichiometric ratio.
The H atoms were placed at calculated positions and were allowed to ride on their respective parent atoms using SHELXL97 (Sheldrick, 1997) defaults.
Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: CAD-4 Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97.
Fig. 1. The structure of (I) with 50% probability displacement ellipsoids. | |
Fig. 2. Packing of the molecules of (I) viewed down the b axis. |
[ZnCl2(C5H11NO2)2] | F(000) = 768 |
Mr = 370.57 | Dx = 1.503 Mg m−3 Dm = 1.52 Mg m−3 Dm measured by flotation in a mixture of xylene and bromoform |
Monoclinic, C2/c | Cu Kα radiation, λ = 1.54180 Å |
a = 19.997 (2) Å | Cell parameters from 25 reflections |
b = 6.2259 (10) Å | θ = 15–27° |
c = 13.5028 (10) Å | µ = 5.19 mm−1 |
β = 103.02 (2)° | T = 293 K |
V = 1637.9 (3) Å3 | Plates, colorless |
Z = 4 | 0.24 × 0.18 × 0.10 mm |
Enraf-Nonius CAD-4 diffractometer | 1394 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.048 |
Graphite monochromator | θmax = 67.9°, θmin = 4.5° |
ω–2θ scans | h = −24→23 |
Absorption correction: ψ scan (North et al., 1968) | k = 0→7 |
Tmin = 0.40, Tmax = 0.60 | l = −15→16 |
1526 measured reflections | 2 standard reflections every 100 reflections |
1435 independent reflections | intensity decay: <2% |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.053 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.137 | H-atom parameters constrained |
S = 1.11 | w = 1/[σ2(Fo2) + (0.1048P)2 + 1.3333P] where P = (Fo2 + 2Fc2)/3 |
1435 reflections | (Δ/σ)max < 0.001 |
87 parameters | Δρmax = 1.06 e Å−3 |
0 restraints | Δρmin = −0.89 e Å−3 |
[ZnCl2(C5H11NO2)2] | V = 1637.9 (3) Å3 |
Mr = 370.57 | Z = 4 |
Monoclinic, C2/c | Cu Kα radiation |
a = 19.997 (2) Å | µ = 5.19 mm−1 |
b = 6.2259 (10) Å | T = 293 K |
c = 13.5028 (10) Å | 0.24 × 0.18 × 0.10 mm |
β = 103.02 (2)° |
Enraf-Nonius CAD-4 diffractometer | 1394 reflections with I > 2σ(I) |
Absorption correction: ψ scan (North et al., 1968) | Rint = 0.048 |
Tmin = 0.40, Tmax = 0.60 | 2 standard reflections every 100 reflections |
1526 measured reflections | intensity decay: <2% |
1435 independent reflections |
R[F2 > 2σ(F2)] = 0.053 | 0 restraints |
wR(F2) = 0.137 | H-atom parameters constrained |
S = 1.11 | Δρmax = 1.06 e Å−3 |
1435 reflections | Δρmin = −0.89 e Å−3 |
87 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
Zn1 | 0.0000 | 0.23870 (6) | 0.7500 | 0.0332 (3) | |
Cl1 | 0.08490 (3) | 0.03328 (12) | 0.83847 (5) | 0.0481 (3) | |
N1 | −0.06037 (12) | 0.8226 (3) | 0.89686 (18) | 0.0377 (5) | |
H1A | −0.0770 | 0.9442 | 0.9163 | 0.057* | |
H1B | −0.0694 | 0.8170 | 0.8293 | 0.057* | |
H1C | −0.0152 | 0.8178 | 0.9213 | 0.057* | |
O1 | −0.03602 (11) | 0.4567 (3) | 0.82769 (16) | 0.0458 (5) | |
O2 | −0.06796 (12) | 0.2625 (3) | 0.94793 (18) | 0.0442 (6) | |
C2 | −0.09324 (13) | 0.6360 (4) | 0.93640 (19) | 0.0323 (6) | |
H2 | −0.0814 | 0.6406 | 1.0109 | 0.039* | |
C3 | −0.17161 (15) | 0.6472 (5) | 0.9000 (3) | 0.0519 (8) | |
H3 | −0.1856 | 0.7939 | 0.9122 | 0.062* | |
C1 | −0.06352 (11) | 0.4305 (4) | 0.90147 (19) | 0.0304 (5) | |
C4 | −0.2063 (2) | 0.4966 (8) | 0.9619 (4) | 0.0842 (14) | |
H4A | −0.2552 | 0.5059 | 0.9379 | 0.126* | |
H4B | −0.1939 | 0.5372 | 1.0322 | 0.126* | |
H4C | −0.1916 | 0.3519 | 0.9544 | 0.126* | |
C5 | −0.19570 (19) | 0.6031 (6) | 0.7863 (3) | 0.0724 (11) | |
H5A | −0.1735 | 0.7011 | 0.7491 | 0.109* | |
H5B | −0.2445 | 0.6222 | 0.7662 | 0.109* | |
H5C | −0.1842 | 0.4583 | 0.7722 | 0.109* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Zn1 | 0.0409 (4) | 0.0207 (3) | 0.0424 (4) | 0.000 | 0.0188 (3) | 0.000 |
Cl1 | 0.0471 (4) | 0.0421 (5) | 0.0536 (5) | 0.0102 (3) | 0.0083 (3) | −0.0017 (3) |
N1 | 0.0418 (12) | 0.0209 (10) | 0.0499 (13) | −0.0003 (8) | 0.0090 (10) | −0.0016 (9) |
O1 | 0.0649 (13) | 0.0294 (10) | 0.0527 (12) | 0.0067 (8) | 0.0334 (10) | −0.0019 (8) |
O2 | 0.0555 (13) | 0.0218 (10) | 0.0590 (14) | 0.0052 (7) | 0.0211 (11) | 0.0057 (7) |
C2 | 0.0408 (13) | 0.0203 (11) | 0.0391 (13) | 0.0034 (9) | 0.0160 (11) | −0.0005 (9) |
C3 | 0.0369 (14) | 0.0358 (15) | 0.087 (2) | 0.0070 (11) | 0.0213 (14) | 0.0019 (14) |
C1 | 0.0302 (11) | 0.0209 (11) | 0.0407 (13) | 0.0031 (9) | 0.0092 (10) | −0.0019 (9) |
C4 | 0.058 (2) | 0.078 (3) | 0.134 (4) | −0.0003 (19) | 0.057 (2) | 0.011 (3) |
C5 | 0.0461 (17) | 0.065 (2) | 0.093 (3) | −0.0020 (16) | −0.0128 (17) | 0.007 (2) |
Zn1—O1 | 1.9500 (18) | C2—C3 | 1.535 (4) |
Zn1—O1i | 1.9500 (18) | C2—H2 | 0.9800 |
Zn1—Cl1i | 2.2430 (8) | C3—C4 | 1.522 (5) |
Zn1—Cl1 | 2.2430 (8) | C3—C5 | 1.526 (5) |
N1—C2 | 1.492 (3) | C3—H3 | 0.9800 |
N1—H1A | 0.8900 | C4—H4A | 0.9600 |
N1—H1B | 0.8900 | C4—H4B | 0.9600 |
N1—H1C | 0.8900 | C4—H4C | 0.9600 |
O1—C1 | 1.252 (3) | C5—H5A | 0.9600 |
O2—C1 | 1.233 (3) | C5—H5B | 0.9600 |
C2—C1 | 1.529 (3) | C5—H5C | 0.9600 |
O1—Zn1—O1i | 91.77 (12) | C4—C3—C2 | 110.7 (3) |
O1—Zn1—Cl1i | 110.88 (7) | C5—C3—C2 | 112.5 (3) |
O1i—Zn1—Cl1i | 115.94 (7) | C4—C3—H3 | 107.4 |
O1—Zn1—Cl1 | 115.94 (7) | C5—C3—H3 | 107.4 |
O1i—Zn1—Cl1 | 110.88 (7) | C2—C3—H3 | 107.4 |
Cl1i—Zn1—Cl1 | 110.47 (4) | O2—C1—O1 | 127.6 (2) |
C2—N1—H1A | 109.5 | O2—C1—C2 | 118.4 (2) |
C2—N1—H1B | 109.5 | O1—C1—C2 | 114.0 (2) |
H1A—N1—H1B | 109.5 | C3—C4—H4A | 109.5 |
C2—N1—H1C | 109.5 | C3—C4—H4B | 109.5 |
H1A—N1—H1C | 109.5 | H4A—C4—H4B | 109.5 |
H1B—N1—H1C | 109.5 | C3—C4—H4C | 109.5 |
C1—O1—Zn1 | 128.24 (17) | H4A—C4—H4C | 109.5 |
N1—C2—C1 | 107.9 (2) | H4B—C4—H4C | 109.5 |
N1—C2—C3 | 110.5 (2) | C3—C5—H5A | 109.5 |
C1—C2—C3 | 112.3 (2) | C3—C5—H5B | 109.5 |
N1—C2—H2 | 108.7 | H5A—C5—H5B | 109.5 |
C1—C2—H2 | 108.7 | C3—C5—H5C | 109.5 |
C3—C2—H2 | 108.7 | H5A—C5—H5C | 109.5 |
C4—C3—C5 | 111.2 (3) | H5B—C5—H5C | 109.5 |
O1i—Zn1—O1—C1 | −174.3 (3) | Zn1—O1—C1—O2 | 7.7 (4) |
Cl1i—Zn1—O1—C1 | 67.0 (2) | Zn1—O1—C1—C2 | −173.36 (17) |
Cl1—Zn1—O1—C1 | −60.0 (2) | N1—C2—C1—O2 | 159.6 (2) |
N1—C2—C3—C4 | −164.4 (3) | C3—C2—C1—O2 | −78.4 (3) |
C1—C2—C3—C4 | 75.0 (4) | N1—C2—C1—O1 | −19.4 (3) |
N1—C2—C3—C5 | 70.5 (3) | C3—C2—C1—O1 | 102.6 (3) |
C1—C2—C3—C5 | −50.1 (3) |
Symmetry code: (i) −x, y, −z+3/2. |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···O2ii | 0.89 | 2.03 | 2.837 (3) | 151 |
N1—H1B···Cl1iii | 0.89 | 2.59 | 3.370 (2) | 146 |
N1—H1C···O2iv | 0.89 | 2.19 | 2.972 (3) | 146 |
Symmetry codes: (ii) x, y+1, z; (iii) −x, y+1, −z+3/2; (iv) −x, −y+1, −z+2. |
Experimental details
Crystal data | |
Chemical formula | [ZnCl2(C5H11NO2)2] |
Mr | 370.57 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 293 |
a, b, c (Å) | 19.997 (2), 6.2259 (10), 13.5028 (10) |
β (°) | 103.02 (2) |
V (Å3) | 1637.9 (3) |
Z | 4 |
Radiation type | Cu Kα |
µ (mm−1) | 5.19 |
Crystal size (mm) | 0.24 × 0.18 × 0.10 |
Data collection | |
Diffractometer | Enraf-Nonius CAD-4 diffractometer |
Absorption correction | ψ scan (North et al., 1968) |
Tmin, Tmax | 0.40, 0.60 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 1526, 1435, 1394 |
Rint | 0.048 |
(sin θ/λ)max (Å−1) | 0.601 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.053, 0.137, 1.11 |
No. of reflections | 1435 |
No. of parameters | 87 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 1.06, −0.89 |
Computer programs: CAD-4 Software (Enraf-Nonius, 1989), CAD-4 Software, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 1999), SHELXL97.
Zn1—O1 | 1.9500 (18) | C2—C1 | 1.529 (3) |
Zn1—Cl1 | 2.2430 (8) | C2—C3 | 1.535 (4) |
N1—C2 | 1.492 (3) | C3—C4 | 1.522 (5) |
O1—C1 | 1.252 (3) | C3—C5 | 1.526 (5) |
O2—C1 | 1.233 (3) | ||
O1—Zn1—O1i | 91.77 (12) | C4—C3—C5 | 111.2 (3) |
O1—Zn1—Cl1i | 110.88 (7) | C4—C3—C2 | 110.7 (3) |
O1—Zn1—Cl1 | 115.94 (7) | C5—C3—C2 | 112.5 (3) |
N1—C2—C1 | 107.9 (2) | O2—C1—O1 | 127.6 (2) |
N1—C2—C3 | 110.5 (2) | O2—C1—C2 | 118.4 (2) |
C1—C2—C3 | 112.3 (2) | O1—C1—C2 | 114.0 (2) |
N1—C2—C3—C4 | −164.4 (3) | N1—C2—C1—O2 | 159.6 (2) |
C1—C2—C3—C4 | 75.0 (4) | C3—C2—C1—O2 | −78.4 (3) |
N1—C2—C3—C5 | 70.5 (3) | N1—C2—C1—O1 | −19.4 (3) |
C1—C2—C3—C5 | −50.1 (3) | C3—C2—C1—O1 | 102.6 (3) |
Symmetry code: (i) −x, y, −z+3/2. |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···O2ii | 0.89 | 2.03 | 2.837 (3) | 150.8 |
N1—H1B···Cl1iii | 0.89 | 2.59 | 3.370 (2) | 146.3 |
N1—H1C···O2iv | 0.89 | 2.19 | 2.972 (3) | 146.0 |
Symmetry codes: (ii) x, y+1, z; (iii) −x, y+1, −z+3/2; (iv) −x, −y+1, −z+2. |
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Valine, an essential amino acid, is often found in the interior of protein molecules due to its hydrophobic nature and thus plays a key role in determining their three-dimensional structure. Structural data on simple valine–inorganic salt complexes seem to be very limited. Apart from the present study which reports the crystal structure of (I), a complex of DL-valine with ZnCl2, namely dichlorobis(DL-valinato)zinc(II), the structure of DL-valine with CaCl2 (Glowiak & Ciunik, 1978) remains the only other complex that has been reported so far. Zinc, which competes successfully with cadmium for protein-binding sites, also plays an important biological role in the form of a structural motif called zinc fingers. Interestingly, zinc finger motifs are characteristic of certain proteins that have an affinity to bind to DNA. Recently, the crystal structures of trichloro(sarcosinio)zinc(II) monohydrate (Krishnakumar et al., 2001) and dichlorobis(sarcosinato)zinc(II) (Subha Nandhini et al., 2001) have been reported.
Fig. 1 shows the molecular structure and the atom-numbering scheme adopted. Zn atom lies on the two fold axis within the unit cell with two symmetrically related valine molecules coordinating to it as ligands. Valine exists as a zwitterion as expected with C1—O1 and C1—O2 bond distances of 1.252 (3) and 1.233 (3) Å, respectively. This observed asymmetry of the carboxylate group is most likely a result of the participation of only one of the carboxyl O atoms (O1) in the coordination environment. The carboxylate group is quite planar and the amino nitrogen deviates from this plane by 0.486 (4) Å, leading to the twisting of the C—N bond out of the plane of the carboxyl group by 19.9 (3)°. The conformation of the valine molecule determined by the internal rotational angles ψ2 [-19.4 (3)], χ11 [-164.4 (3)° and χ12 [70.5 (3)] agree well with the values observed for the monoclinic form of DL-valine (Mallikarjunan & Rao, 1969) and for the triclinic form of DL-valine (Dalhus & Gorbitz, 1996).
Zinc is known to have both tetrahedral and octahedral coordination in crystal structures (Cingi et al., 1972). In the present structure, zinc has a distorted tetrahedral environment with twofold related Cl atoms and two carboxyl O atoms, one each from the twofold-related valine molecules in the asymmetric unit. Similar metal–ligand coordination is observed in the crystal structures of glycine with ZnCl2 (Hariharan et al., 1989) and L-proline with ZnCl2 (Yukawa et al., 1985). However, in the complexes of ZnCl2 with L-histidine (Foster et al., 1993) and sarcosine (Krishnakumar et al., 2001), the Zn atom exhibits a different coordination environment with one of the carboxyl O and three Cl atoms participating in it. Interestingly, in both these structures, the amino acid exists in an unusual cationic form.
Fig. 2 shows the packing of the molecules of (I) viewed down the b axis. The valine molecules coordinating to Zn through O1 form a linear chain characterized by a head-to-tail hydrogen bond between the centrosymmetrically related valine molecules and an N—H···Cl hydrogen bond. The linear chain, on either side, is flanked by the hydrophobic side chains of valine leading to alternating polar and non-polar regions along the a axis. This chain forms an infinite two-dimensional layered network parallel to the bc plane through head-to-tail hydrogen bonds between translationally related valine molecules along the b axis. O1 of the carboxyl group does not participate in the hydrogen bonding network and the strengths of the two head-to-tail hydrogen bonds involving O2 are nearly equal. Though the metal–ligand coordination observed in (I) is similar to those observed in some amino acid–ZnCl2 complexes, the crystal structure itself does not bear any similarities with them.