Di­chloro­bis­(sarcosinato)­zinc(II)

In the title compound, [ZnCl₂(CH₃NH₂⁺CH₂COO⁻)₂], the sarcosine ligand coordinates to the metal in the zwitterionic form. The Zn atom has a distorted tetrahedral coordination with two Cl atoms and two O atoms, one each from the two crystallographically independent sarcosine mol­ecules in the asymmetric unit. Head-to-tail hydrogen bonds between the amino acid mol­ecules, in addition to N—H...Cl, C—H...O and C—H...Cl hydrogen bonds, stabilize the packing of the mol­ecules.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.028
• wR factor = 0.075
• Data-to-parameter ratio = 15.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

Sarcosine (N-methylglycine, CH₃NH₂⁺CH₂COO^-), an intermediate in the metabolism of choline, occurs naturally in large amounts in starfish and sea urchins. The crystal structure of sarcosine itself was previously determined in our laboratory (Mostad & Natarajan, 1989). Zinc–amino acid complexes are interesting as zinc is known to compete successfully with cadmium for protein binding sites. Zinc also plays an important biological role in the formation of a structural motif called zinc fingers which are characteristic of certain proteins that bind to DNA. Recently, the crystal structure of a complex of sarcosine with zinc chloride, namely trichloro(sarcosinio)zinc(II) monohydrate (Krishnakumar et al., 2001), in which the amino acid exhibits an unusual cationic form, was reported. The present work reports the crystal structure of a complex, (I), of sarcosine with zinc chloride where the amino acid adopts the usually expected zwitterionic form. The crystal structures of complexes of ZnCl₂ with glycine (Hariharan et al., 1989), L-proline (Yukawa et al., 1985) and L-histidine (Foster et al., 1993) have already been reported.

In Fig. 1, the molecular structure and atom-numbering scheme adopted by (I) are shown. Both the sarcosine molecules in the asymmetric unit exist as zwitterions each with a positively charged amino group and a negatively charged carboxylate group. However, the C1—O1 and C1—O2 bond lengths in molecule A [1.276 (3) and 1.223 (3) Å, respectively] and molecule B [1.261 (3) and 1.213 (3) Å, respectively] show significant deviations from those usually exhibited by a zwitterion. The larger value observed in the C1—O1 bond lengths may be due to the fact that both the O1 atoms of molecule A and B participate in the coordination environment around the metal. The angle between the planes formed by the atoms of the two sarcosine molecules coordinating to Zn is 81.5 (1)°.

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 two Cl atoms and two carboxyl O atoms, one each from the two crystallographically independent sarcosine molecules in the asymmetric unit. The angles around the Zn atom range from 101.36 (5) to 115.74 (3)°. The coordination environment around Zn in trichloro(sarcosinio)zinc(II) monohydrate, however, is different since it involves three chlorines and one of the carboxyl O atoms.

Head-to-tail hydrogen bonds between the amino acid molecules, in addition to N—H···Cl, C—H···O and C—H···Cl hydrogen bonds, stabilize the three-dimensional network of the molecules. The crystal structure of (I) does not bear any relation either to that of trichloro(sarcosinio)zinc(II) monohydrate or to those of sarcosine cadmium chloride (Krishnakumar et al., 1996) and sarcosine barium chloride tetrahydrate (Krishnakumar & Natarajan, 1995). However, the unit-cell parameters of (I) and those of sarcosine barium chloride tetrahydrate bear an interesting relationship as b and c axes in them are very nearly equal and the cell length a in (I) is twice that of the other.

S2. Experimental

Colourless single crystals of (I) were grown as transparent needles from a saturated water–acetone mixture containing sarcosine and zinc chloride in stoichiometric ratio.

S3. Refinement

The H atoms were placed in calculated positions and were allowed to ride on their respective parent atoms using SHELXL97 (Sheldrick, 1997) defaults.

Computing details

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.

Figures

Fig. 1. The structure of (I) with 50% probability displacement ellipsoids.

Dichlorobis(sarcosinato)zinc(II)

Crystal data

[ZnCl2(C6H14N2O4)]	Dx = 1.736 Mg m^−3 Dm = 1.74 Mg m^−3 Dm measured by floatation in a mixture of carbon tetrachloride and bromoform
Mr = 314.46	Cu Kα radiation, λ = 1.54180 Å
Orthorhombic, Pbca	Cell parameters from 25 reflections
a = 14.191 (2) Å	θ = 15–27°
b = 10.655 (1) Å	µ = 6.94 mm^−1
c = 15.917 (2) Å	T = 293 K
V = 2406.5 (4) Å^3	Needle, colorless
Z = 8	0.16 × 0.12 × 0.10 mm
F(000) = 1280

Data collection

Enraf-Nonius CAD-4 diffractometer	2004 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.000
Graphite monochromator	θmax = 67.9°, θmin = 5.6°
ω–2θ scans	h = 0→16
Absorption correction: ψ scan (North et al., 1968)	k = 0→12
Tmin = 0.400, Tmax = 0.503	l = 0→19
2182 measured reflections	2 standard reflections every 200 reflections
2182 independent reflections	intensity decay: 0.1%

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)] = 0.028	H-atom parameters constrained
wR(F^2) = 0.075	w = 1/[σ^2(Fo^2) + (0.0299P)^2 + 2.1069P] where P = (Fo^2 + 2Fc^2)/3
S = 1.18	(Δ/σ)max = 0.001
2182 reflections	Δρmax = 0.28 e Å^−3
137 parameters	Δρmin = −0.43 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: 0.00071 (4)

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
Zn1	0.91616 (2)	0.26684 (3)	0.374714 (18)	0.02767 (13)
Cl1	0.82235 (4)	0.23686 (7)	0.26065 (4)	0.04149 (18)
Cl2	0.85109 (5)	0.21851 (6)	0.50017 (4)	0.04106 (18)
O1A	0.96149 (12)	0.43918 (17)	0.36814 (12)	0.0407 (5)
O1B	1.02354 (12)	0.15641 (18)	0.34808 (11)	0.0386 (4)
O2A	0.81985 (13)	0.51561 (19)	0.40136 (14)	0.0474 (5)
O2B	1.10244 (14)	0.1897 (2)	0.46595 (12)	0.0502 (5)
N1A	0.86855 (15)	0.75410 (19)	0.36977 (12)	0.0324 (5)
H1A1	0.8531	0.7594	0.4245	0.039*
H1A2	0.8165	0.7310	0.3414	0.039*
N1B	1.24257 (13)	0.0311 (2)	0.42703 (13)	0.0322 (5)
H1B1	1.2600	0.1064	0.4473	0.039*
H1B2	1.2212	−0.0151	0.4704	0.039*
C1A	0.90174 (17)	0.5272 (2)	0.37881 (14)	0.0303 (5)
C1B	1.09122 (16)	0.1399 (2)	0.39819 (14)	0.0277 (5)
C2A	0.94081 (17)	0.6563 (2)	0.35948 (16)	0.0323 (5)
H2A1	0.9933	0.6737	0.3967	0.039*
H2A2	0.9642	0.6578	0.3022	0.039*
C2B	1.16529 (17)	0.0490 (3)	0.36588 (15)	0.0322 (5)
H2B1	1.1359	−0.0314	0.3543	0.039*
H2B2	1.1911	0.0807	0.3136	0.039*
C3A	0.8985 (2)	0.8799 (3)	0.3400 (2)	0.0554 (8)
H3A1	0.8482	0.9389	0.3486	0.083*
H3A2	0.9135	0.8758	0.2813	0.083*
H3A3	0.9530	0.9065	0.3709	0.083*
C3B	1.32584 (18)	−0.0316 (3)	0.39022 (18)	0.0448 (7)
H3B1	1.3737	−0.0405	0.4324	0.067*
H3B2	1.3498	0.0180	0.3446	0.067*
H3B3	1.3081	−0.1130	0.3697	0.067*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.01822 (19)	0.0360 (2)	0.0288 (2)	0.00084 (12)	0.00124 (11)	−0.00157 (13)
Cl1	0.0290 (3)	0.0618 (4)	0.0337 (3)	0.0001 (3)	−0.0053 (2)	−0.0061 (3)
Cl2	0.0417 (3)	0.0462 (4)	0.0353 (3)	−0.0046 (3)	0.0121 (3)	0.0024 (3)
O1A	0.0235 (9)	0.0372 (10)	0.0614 (12)	−0.0007 (8)	0.0015 (8)	−0.0009 (9)
O1B	0.0285 (9)	0.0559 (11)	0.0314 (9)	0.0152 (9)	−0.0047 (7)	−0.0046 (8)
O2A	0.0295 (9)	0.0469 (11)	0.0658 (13)	−0.0015 (8)	0.0147 (9)	0.0044 (10)
O2B	0.0392 (10)	0.0691 (14)	0.0423 (11)	0.0155 (10)	−0.0106 (9)	−0.0204 (10)
N1A	0.0285 (11)	0.0370 (11)	0.0318 (11)	−0.0016 (9)	−0.0017 (8)	−0.0007 (9)
N1B	0.0213 (9)	0.0401 (11)	0.0352 (11)	0.0056 (9)	0.0004 (8)	0.0007 (9)
C1A	0.0257 (12)	0.0403 (14)	0.0249 (12)	−0.0039 (10)	−0.0008 (9)	−0.0016 (10)
C1B	0.0213 (11)	0.0359 (12)	0.0259 (11)	−0.0018 (10)	0.0014 (9)	0.0021 (10)
C2A	0.0254 (12)	0.0374 (13)	0.0340 (12)	−0.0033 (11)	0.0011 (10)	−0.0012 (11)
C2B	0.0242 (12)	0.0431 (14)	0.0294 (12)	0.0057 (11)	−0.0012 (9)	−0.0012 (10)
C3A	0.0547 (18)	0.0411 (16)	0.070 (2)	−0.0005 (14)	0.0015 (17)	0.0141 (15)
C3B	0.0243 (13)	0.0592 (18)	0.0509 (16)	0.0142 (12)	0.0065 (12)	0.0070 (14)

Geometric parameters (Å, º)

Zn1—O1A	1.9484 (19)	N1B—H1B1	0.90
Zn1—O1B	1.9713 (17)	N1B—H1B2	0.90
Zn1—Cl2	2.2595 (7)	C1A—C2A	1.514 (3)
Zn1—Cl1	2.2739 (7)	C1B—C2B	1.519 (3)
O1A—C1A	1.276 (3)	C2A—H2A1	0.97
O1B—C1B	1.261 (3)	C2A—H2A2	0.97
O2A—C1A	1.223 (3)	C2B—H2B1	0.97
O2B—C1B	1.213 (3)	C2B—H2B2	0.97
N1A—C2A	1.471 (3)	C3A—H3A1	0.96
N1A—C3A	1.484 (3)	C3A—H3A2	0.96
N1A—H1A1	0.90	C3A—H3A3	0.96
N1A—H1A2	0.90	C3B—H3B1	0.96
N1B—C3B	1.478 (3)	C3B—H3B2	0.96
N1B—C2B	1.479 (3)	C3B—H3B3	0.96
O1A—Zn1—O1B	107.20 (8)	O1B—C1B—C2B	113.7 (2)
O1A—Zn1—Cl2	113.40 (6)	N1A—C2A—C1A	111.4 (2)
O1B—Zn1—Cl2	111.71 (6)	N1A—C2A—H2A1	109.3
O1A—Zn1—Cl1	106.43 (6)	C1A—C2A—H2A1	109.3
O1B—Zn1—Cl1	101.36 (5)	N1A—C2A—H2A2	109.3
Cl2—Zn1—Cl1	115.74 (3)	C1A—C2A—H2A2	109.3
C1A—O1A—Zn1	117.80 (16)	H2A1—C2A—H2A2	108.0
C1B—O1B—Zn1	122.43 (16)	N1B—C2B—C1B	111.88 (19)
C2A—N1A—C3A	113.9 (2)	N1B—C2B—H2B1	109.2
C2A—N1A—H1A1	108.8	C1B—C2B—H2B1	109.2
C3A—N1A—H1A1	108.8	N1B—C2B—H2B2	109.2
C2A—N1A—H1A2	108.8	C1B—C2B—H2B2	109.2
C3A—N1A—H1A2	108.8	H2B1—C2B—H2B2	107.9
H1A1—N1A—H1A2	107.7	N1A—C3A—H3A1	109.5
C3B—N1B—C2B	112.97 (19)	N1A—C3A—H3A2	109.5
C3B—N1B—H1B1	109.0	H3A1—C3A—H3A2	109.5
C2B—N1B—H1B1	109.0	N1A—C3A—H3A3	109.5
C3B—N1B—H1B2	109.0	H3A1—C3A—H3A3	109.5
C2B—N1B—H1B2	109.0	H3A2—C3A—H3A3	109.5
H1B1—N1B—H1B2	107.8	N1B—C3B—H3B1	109.5
O2A—C1A—O1A	126.6 (2)	N1B—C3B—H3B2	109.5
O2A—C1A—C2A	120.0 (2)	H3B1—C3B—H3B2	109.5
O1A—C1A—C2A	113.4 (2)	N1B—C3B—H3B3	109.5
O2B—C1B—O1B	127.0 (2)	H3B1—C3B—H3B3	109.5
O2B—C1B—C2B	119.3 (2)	H3B2—C3B—H3B3	109.5
O1B—Zn1—O1A—C1A	176.31 (17)	Zn1—O1B—C1B—O2B	−2.6 (4)
Cl2—Zn1—O1A—C1A	−59.92 (18)	Zn1—O1B—C1B—C2B	178.76 (16)
Cl1—Zn1—O1A—C1A	68.47 (18)	C3A—N1A—C2A—C1A	−171.6 (2)
O1A—Zn1—O1B—C1B	72.3 (2)	O2A—C1A—C2A—N1A	−1.3 (3)
Cl2—Zn1—O1B—C1B	−52.5 (2)	O1A—C1A—C2A—N1A	178.0 (2)
Cl1—Zn1—O1B—C1B	−176.30 (18)	C3B—N1B—C2B—C1B	−166.3 (2)
Zn1—O1A—C1A—O2A	8.0 (3)	O2B—C1B—C2B—N1B	2.1 (3)
Zn1—O1A—C1A—C2A	−171.24 (15)	O1B—C1B—C2B—N1B	−179.2 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1A—H1A1···O2B^i	0.90	1.93	2.714 (3)	144
N1A—H1A2···Cl1^ii	0.90	2.35	3.223 (2)	163
N1B—H1B1···Cl2^iii	0.90	2.42	3.291 (2)	164
N1B—H1B2···Cl2^iv	0.90	2.44	3.191 (2)	141
N1B—H1B2···O2A^iii	0.90	2.48	2.985 (3)	116
C2A—H2A2···O1B^v	0.97	2.40	3.342 (3)	164
C2B—H2B2···Cl1^vi	0.97	2.76	3.610 (3)	146
C3A—H3A1···O2A^ii	0.96	2.66	3.555 (4)	156

Symmetry codes: (i) −x+2, −y+1, −z+1; (ii) −x+3/2, y+1/2, z; (iii) x+1/2, −y+1/2, −z+1; (iv) −x+2, −y, −z+1; (v) −x+2, y+1/2, −z+1/2; (vi) x+1/2, y, −z+1/2.