Tri­chloro­(sarcosinio)­zinc(II) monohydrate

In the title compound, [ZnCl₃(C₃H₈NO₂)]·H₂O, the sarcosine ligand unexpectedly coordinates to the metal in the cationic form (CH₃–NH₂⁺–CH₂–COOH). The Zn atom is found to have tetrahedral coordination. A head-to-tail N—H...O hydrogen bond between the screw-related mol­ecules is present. The water mol­ecule does not participate in metal coordination, but co-operates in the packing as a donor and acceptor in hydrogen bonds to a carboxyl O atom and as a donor to a Cl atom.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.006 Å
• R factor = 0.017
• wR factor = 0.053
• Data-to-parameter ratio = 9.2

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



ABSTM_02  Alert C The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
          Tmin and Tmax reported:      0.812     0.993
          Tmin and Tmax expected:      0.400     0.675
          RR =      1.380
          Please check that your absorption correction is appropriate.

General Notes



ABSTM_02  When printed, the submitted absorption T values will be replaced
          by the scaled T values. Since the ratio of scaled T's is
          identical to the ratio of reported T values, the scaling does
          not imply a change to the absorption corrections used in the
          study.
          Ratio of Tmax expected/reported      0.679
          Tmax scaled      0.675 Tmin scaled      0.552

REFLT_03
         From the CIF: _diffrn_reflns_theta_max           24.97
         From the CIF: _reflns_number_total                933
         Count of symmetry unique reflns          933
         Completeness (_total/calc)            100.00%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured         0
         Fraction of Friedel pairs measured     0.000
         Are heavy atom types Z>Si present          yes
          WARNING: Large fraction of Friedel related reflns may
                   be needed to determine absolute structure


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

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S1. Comment

Sarcosine (N-methylglycine, CH₃NH₂⁺CH₂COO^-), an α-amino acid present in several biologically important compounds, forms a number of addition compounds with inorganic acids and salts besides forming metallic complexes. The crystal structure of sarcosine itself was determined earlier in our laboratory (Mostad & Natarajan, 1989). The present study reports the crystal structure of a complex of sarcosine with ZnCl₂, namely trichloro(sarcosinio)zinc(II) monohydrate, (I).

The sarcosine molecule exists in the cationic form with a positively charged amino group and a protonated carboxylic acid group. In the cases of complexes with metallic salts, the amino acid normally remains as a zwitterion. The formation of the zinc complex observed in the crystals may be justified by a complex series of hydrolytic equilibria involving the solvent water molecules, the Cl^- ions and the sarcosine zwitterion. In the three other crystal structures of amino acid complexes with ZnCl₂ known so far, amino acid molecules exist as zwitterions in glycine with ZnCl₂ (Hariharan et al., 1989) and L-proline with ZnCl₂ (Yukawa et al., 1985) and adopts a cationic form in L-histidine with ZnCl₂ (Foster et al., 1993).

In Fig. 1, the molecular structure and the atom-numbering scheme adopted is shown. The molecular main chain deviates from planarity, the C3—N1—C2—C1 torsion angle (Table 1) indicating that the C3—N1 bond is synclinal to C2—C1. Similar observations have been made in the structures of sarcosine cadmium chloride (Krishnakumar & Natarajan, 1996), sarcosine telluric acid adduct (Averbuch-pouchot, 1988) and sarcosinium tartrate (Krishnakumar et al., 2001). C3—N1 is antiperiplanar to C2—C1 in the crystal structure of sarcosine (Mostad & Natarajan, 1989), sarcosine barium chloride (Krishnakumar et al., 1995), sarcosine sucrose (Krishnakumar & Natarajan et al., 1995), sarcosine oxalic acid monohydrate (Krishnakumar et al., 1999) and diaquabis(sarcosinato)copper(II) (Krishnakumar et al., 1994). The value of the O1—C1—O2—H1 torsion angle is -85.6°. This unusual value observed may be justified by the fact that the position of the hydrogen (H1) is determined by the two hydrogen bonds O2—H1···O1Wⁱ (intermolecular) and N1—H1B···O2 (intramolecular), in which O2 is involved [symmetry code: (i) x + 1, y, z]. It is important to notice that both these hydrogen bonds justify the cationic status of the coordinating amino-acid ligand (see Table 2). It is interesting to notice also that the C1—O1 bond distance is remarkably longer than C1—O2 (Δ/σ = 10.25) (see Table 1), when usually in carboxylic acids, the contrary is observed [sp²═O = 1.214 (19) Å and Csp²—OH = 1.308 (19) Å; Allen et al., 1987] and is justified by the coordination of O1 to metal and the hydrogen bond O2 forms with the water molecule.

Zinc is known to have both tetrahedral and octahedral coordination in crystal structures (Cingi et al., 1972). Zinc in the present structure has a tetrahedral coordination with three chlorines and a carboxyl O atom of the amino acid taking part. The angles around the Zn atom range from 104.2 (1) to 115.4 (1)°. Fig. 2 shows the packing of the molecules viewed down the b axis. A head-to-tail N—H···O hydrogen bond between the screw-related molecules is present. One of the three chlorines participates in a C—H···Cl hydrogen bond (see Table 2). The N1—H1A···O1ⁱⁱ and N1—H1B···Clⁱⁱⁱ hydrogen bonds form a ring of R₄⁴(12) graph-set motif (Etter et al., 1990), while the O2—H1···O1Wⁱ and O1W—H2W···Cl3 interactions form a C₂²(8) chain running along [100] [symmetry codes: (ii) 2 - x, y - 1/2, -z; (iii) x, y - 1, z].

S2. Experimental

Colourless single crystals of the title complex were grown as transparent needles from a saturated aqueous solution containing sarcosine and zinc chloride in a stoichiometric ratio.

S3. Refinement

H atoms were placed at calculated positions and were allowed to ride on their respective parent atoms using SHELXL97 (Sheldrick, 1997) defaults. The positions of the water H atoms were calculated using HYDROGEN (Nardelli, 1999), with O—H = 0.85 Å, H—O—H = 107° and U(H)_eq= 1.2U_eq of the parent atoms, and were not included in the refinement.

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 molecular structure of (I) with the atom-numbering scheme and 50% probability displacement ellipsoids.
	Fig. 2. Packing diagram of the molecules of (I) in the unit cell viewed down the b axis.

'Trichloro(sarcosinium) zinc(II) monohydrate'

Crystal data

[ZnCl3(C3H8NO2)]·H2O	F(000) = 280
Mr = 279.84	Dx = 1.894 Mg m^−3 Dm = 1.90 (3) Mg m^−3 Dm measured by floatation in a mixture of carbon tetrachloride and bromoform
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
a = 6.6181 (12) Å	Cell parameters from 1017 reflections
b = 7.4989 (11) Å	θ = 6–15°
c = 9.900 (4) Å	µ = 3.28 mm^−1
β = 92.62 (2)°	T = 293 K
V = 490.8 (2) Å^3	Plates, colourless
Z = 2	0.38 × 0.24 × 0.12 mm

Data collection

Enraf-Nonius sealed tube diffractometer	913 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.008
Graphite monochromator	θmax = 25.0°, θmin = 2.1°
ω–2θ scans	h = 0→7
Absorption correction: ψ scan (North et al., 1968)	k = 0→8
Tmin = 0.812, Tmax = 0.993	l = −11→11
1017 measured reflections	2 standard reflections every 200 reflections
933 independent reflections	intensity decay: 0.1%

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.017	w = 1/[σ^2(Fo^2) + (0.0239P)^2 + 0.1562P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.053	(Δ/σ)max < 0.001
S = 1.28	Δρmax = 0.30 e Å^−3
933 reflections	Δρmin = −0.24 e Å^−3
101 parameters	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 0.051 (4)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack (1983)
Secondary atom site location: difference Fourier map	Absolute structure parameter: 0.010 (18)

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	0.67915 (6)	0.40483 (7)	0.26537 (4)	0.02369 (18)
Cl1	0.86420 (18)	0.66062 (16)	0.26939 (12)	0.0336 (3)
Cl2	0.37724 (17)	0.45863 (16)	0.15902 (13)	0.0368 (3)
Cl3	0.64383 (18)	0.30575 (18)	0.47779 (12)	0.0374 (3)
O1	0.8288 (5)	0.2418 (4)	0.1452 (3)	0.0281 (7)
O2	1.0144 (5)	0.1081 (5)	0.3096 (3)	0.0294 (7)
H1	1.1007	0.1815	0.3336	0.044*
N1	1.2102 (5)	−0.1049 (7)	0.1347 (4)	0.0318 (8)
H1A	1.2284	−0.1872	0.0703	0.038*
H1B	1.1574	−0.1611	0.2053	0.038*
C1	0.9639 (6)	0.1327 (6)	0.1911 (4)	0.0213 (9)
C2	1.0611 (7)	0.0262 (7)	0.0814 (5)	0.0318 (11)
H2A	0.9562	−0.0360	0.0284	0.038*
H2B	1.1275	0.1076	0.0216	0.038*
C3	1.4107 (7)	−0.0335 (7)	0.1794 (6)	0.0383 (12)
H3A	1.4655	0.0341	0.1072	0.057*
H3B	1.5001	−0.1304	0.2032	0.057*
H3C	1.3966	0.0423	0.2565	0.057*
O1W	0.1661 (4)	0.4117 (6)	0.4685 (3)	0.0297 (6)
H1W	0.0981	0.3789	0.5349	0.036*
H2W	0.2062	0.5186	0.4851	0.036*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0218 (3)	0.0221 (3)	0.0272 (3)	0.0014 (2)	0.00139 (16)	0.0002 (2)
Cl1	0.0324 (6)	0.0266 (6)	0.0423 (6)	−0.0071 (5)	0.0061 (5)	−0.0030 (5)
Cl2	0.0278 (6)	0.0390 (8)	0.0426 (6)	0.0047 (4)	−0.0079 (5)	0.0031 (5)
Cl3	0.0374 (6)	0.0450 (8)	0.0305 (6)	0.0116 (6)	0.0085 (5)	0.0086 (5)
O1	0.0320 (17)	0.0245 (16)	0.0280 (16)	0.0076 (14)	0.0032 (13)	0.0010 (14)
O2	0.0337 (18)	0.0299 (17)	0.0250 (17)	0.0040 (14)	0.0031 (13)	−0.0014 (14)
N1	0.0332 (19)	0.0196 (18)	0.043 (2)	0.003 (2)	0.0091 (15)	−0.002 (2)
C1	0.022 (2)	0.018 (2)	0.025 (2)	−0.0030 (17)	0.0043 (16)	−0.0023 (17)
C2	0.035 (2)	0.032 (3)	0.028 (2)	0.010 (2)	0.0010 (19)	−0.007 (2)
C3	0.028 (2)	0.041 (3)	0.046 (3)	0.002 (2)	0.005 (2)	−0.002 (2)
O1W	0.0319 (15)	0.0305 (15)	0.0268 (14)	−0.0015 (18)	0.0032 (11)	−0.0016 (18)

Geometric parameters (Å, º)

Zn1—O1	1.999 (3)	N1—H1B	0.9000
Zn1—Cl2	2.2519 (13)	C1—C2	1.515 (6)
Zn1—Cl3	2.2525 (14)	C2—H2A	0.9700
Zn1—Cl1	2.2751 (13)	C2—H2B	0.9700
O1—C1	1.280 (5)	C3—H3A	0.9600
O2—C1	1.219 (5)	C3—H3B	0.9600
O2—H1	0.8200	C3—H3C	0.9600
N1—C2	1.473 (6)	O1W—H1W	0.850 (3)
N1—C3	1.480 (6)	O1W—H2W	0.857 (4)
N1—H1A	0.9000
O1—Zn1—Cl2	106.53 (10)	O2—C1—C2	120.2 (4)
O1—Zn1—Cl3	115.41 (10)	O1—C1—C2	113.3 (4)
Cl2—Zn1—Cl3	111.58 (5)	N1—C2—C1	113.2 (4)
O1—Zn1—Cl1	104.18 (10)	N1—C2—H2A	108.9
Cl2—Zn1—Cl1	108.82 (5)	C1—C2—H2A	108.9
Cl3—Zn1—Cl1	109.91 (5)	N1—C2—H2B	108.9
C1—O1—Zn1	122.5 (3)	C1—C2—H2B	108.9
C1—O2—H1	109.5	H2A—C2—H2B	107.7
C2—N1—C3	116.3 (4)	N1—C3—H3A	109.5
C2—N1—H1A	108.2	N1—C3—H3B	109.5
C3—N1—H1A	108.2	H3A—C3—H3B	109.5
C2—N1—H1B	108.2	N1—C3—H3C	109.5
C3—N1—H1B	108.2	H3A—C3—H3C	109.5
H1A—N1—H1B	107.4	H3B—C3—H3C	109.5
O2—C1—O1	126.5 (4)	H1W—O1W—H2W	107.0 (3)
Cl2—Zn1—O1—C1	−152.6 (3)	Zn1—O1—C1—C2	−178.5 (3)
Cl3—Zn1—O1—C1	−28.2 (3)	C3—N1—C2—C1	−77.7 (5)
Cl1—Zn1—O1—C1	92.4 (3)	O2—C1—C2—N1	1.4 (6)
Zn1—O1—C1—O2	2.7 (6)	O1—C1—C2—N1	−177.5 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H1···O1W^i	0.82	2.21	2.919 (5)	144
N1—H1A···O1^ii	0.90	2.21	3.001 (5)	146
N1—H1B···O2	0.90	2.48	2.726 (5)	96
N1—H1B···Cl1^iii	0.90	2.46	3.224 (4)	142
O1W—H1W···O2^iv	0.85	2.45	2.943 (5)	118
O1W—H1W···Cl1^v	0.85	2.54	3.220 (4)	138
O1W—H2W···Cl3^iv	0.86	2.39	3.246 (4)	173
C2—H2A···Cl2^vi	0.97	2.82	3.702 (5)	152

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