Sodium hydrogen nitrilo­tri­acetate dihydrate

In the title compound, Na⁺·C₆H₈NO₆^-·2H₂O, the sodium ion is coordinated in a distorted octahedral manner by two carboxyl­ate O atoms and two water O atoms. Each of these water mol­ecules bridges two adjacent Na ions, resulting in two four-membered rings of the type Na-O-Na-O.

S1. Comment

Recently, much attention has been paid to nitrilotriacetate acid (NTA), a multidentate complexing ligand with high specificity for various polyvalent metal ions. The trivalent NTA anion normally coordinates with alkali earth and transition metal ions as tetradentate ligands, binding with an N atom and three acetate O atoms to the metal (Barnett & Uchtman, 1979; Kaneyoshi et al., 1999). However, for a few complexes, NTA is hexadentate or heptadentate (Martin & Jacobson, 1972). The structure of trisodium nitrilotriacetate has been proposed as polymeric with seven O atoms and one N atom coordinated to three sodium ions (Dely, 1967).

The crystal structure of the title compound contains Na ions chelated by NTA molecules via two Na—O bonds [2.436 (2) and 2.345 (2) Å]. The observed Na—O bond distances are within the range 2.28–2.67 Å, reported by Dely (1976). The O—Na—O angle is 88.35 (5)°. Two water molecules are involved in each molecular unit and bridge two adjacent sodium ions, with one water O atom coordinated to Na and Naⁱ, and the other to Na and Naⁱⁱ [symmetry codes: (i) −x, 1 − y, −z; (ii) 1 − x, 1 − y, −z]. The four Na—OW bond distances are in the range 2.345 (2)–2.561 (2) Å and the two OW—Na—OW angles are 91.36 (6) and 88.04 (6)°. The geometry around the sodium ion can be described as slightly distorted octahedral. The infinite crystal network is formed via four-membered Na—OW—Na—OW rings between two layers and via hydrogen bonds between two adjacent molecular units in a given layer.

S2. Experimental

The title compound was obtained in the attempted preparation of an erbium–NTA complex, by mixing 0.50 M Er^III and 0.50 M Na₂NTA aqueous solutions in a 1:4 molar ratio. The pH of the solution was adjusted to 4.5. Colorless microcrystals of the title compound were obtained by slow evaporation.

S3. Refinement

Positional parameters of H atoms bonded to C atoms were calculated geometrically. The H atoms bonded to the N and O atoms were observed from difference syntheses and refined isotropically. The N—H and O—H bond lengths are 0.92 (2) Å and 0.81 (4)–0.90 (3) Å, respectively.

Computing details

Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: SHELXTL (Siemens, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); software used to prepare material for publication: SHELXTL.

Sodium α-hydronitrilotriacetate dihydrate

Crystal data

Na^+·C6H8NO6^−·2H2O	F(000) = 1040
Mr = 249.16	Dx = 1.696 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 42 reflections
a = 5.8620 (19) Å	θ = 6.8–12.6°
b = 12.3986 (16) Å	µ = 0.19 mm^−1
c = 26.854 (3) Å	T = 293 K
V = 1951.8 (7) Å^3	Needle, colourless
Z = 8	0.40 × 0.15 × 0.10 mm

Data collection

Bruker P4 diffractometer	1731 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.035
Graphite monochromator	θmax = 27.5°, θmin = 3.0°
2θ/ω scans	h = −7→7
Absorption correction: ψ scan (North et al., 1968)	k = −16→16
Tmin = 0.873, Tmax = 0.981	l = −34→34
4474 measured reflections	3 standard reflections every 97 reflections
2239 independent reflections	intensity decay: 3.0%

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.038	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.109	H atoms treated by a mixture of independent and constrained refinement
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0544P)^2 + 0.3629P] where P = (Fo^2 + 2Fc^2)/3
2239 reflections	(Δ/σ)max < 0.001
169 parameters	Δρmax = 0.26 e Å^−3
0 restraints	Δρmin = −0.31 e Å^−3

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
Na1	0.24682 (13)	0.53495 (6)	0.03123 (3)	0.0303 (2)
N1	0.1742 (3)	0.69269 (11)	0.15172 (5)	0.0175 (3)
OW1	0.0995 (3)	0.37426 (11)	−0.00484 (6)	0.0314 (3)
OW2	0.3847 (3)	0.56365 (15)	−0.05472 (6)	0.0400 (4)
O1	0.3778 (2)	0.70744 (12)	0.06396 (5)	0.0298 (3)
O2	0.7320 (2)	0.71312 (13)	0.09511 (5)	0.0324 (3)
O3	0.0453 (3)	0.50908 (10)	0.10571 (5)	0.0302 (3)
O4	−0.1266 (2)	0.44076 (11)	0.17261 (5)	0.0302 (3)
O5	0.1241 (2)	0.92952 (9)	0.23208 (5)	0.0236 (3)
O6	0.2442 (2)	0.76159 (9)	0.24822 (5)	0.0236 (3)
C1	0.4274 (3)	0.67261 (15)	0.15004 (6)	0.0228 (4)
H1A	0.4581	0.5973	0.1571	0.027*
H1B	0.5027	0.7159	0.1752	0.027*
C2	0.5209 (3)	0.70163 (14)	0.09849 (6)	0.0222 (4)
C3	0.0433 (3)	0.61089 (13)	0.18141 (6)	0.0201 (3)
H3A	−0.0959	0.6435	0.1938	0.024*
H3B	0.1339	0.5886	0.2098	0.024*
C4	−0.0164 (3)	0.51239 (13)	0.15009 (6)	0.0205 (3)
C5	0.1186 (3)	0.80642 (13)	0.16581 (6)	0.0202 (4)
H5A	−0.0419	0.8198	0.1596	0.024*
H5B	0.2063	0.8554	0.1451	0.024*
C6	0.1704 (3)	0.82886 (13)	0.21995 (6)	0.0188 (3)
HN1	0.126 (4)	0.6857 (18)	0.1193 (9)	0.031 (6)*
HO5	0.134 (5)	0.934 (3)	0.2696 (12)	0.079 (10)*
HW1	0.147 (4)	0.347 (2)	−0.0330 (10)	0.040 (7)*
HW2	0.088 (5)	0.324 (2)	0.0178 (11)	0.054 (8)*
HW3	0.264 (6)	0.542 (2)	−0.0727 (11)	0.056 (9)*
HW4	0.398 (7)	0.629 (4)	−0.0572 (15)	0.107 (15)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Na1	0.0331 (4)	0.0315 (4)	0.0262 (4)	−0.0034 (3)	0.0023 (3)	−0.0045 (3)
N1	0.0205 (7)	0.0159 (7)	0.0161 (7)	−0.0003 (5)	0.0001 (5)	−0.0003 (5)
OW1	0.0428 (8)	0.0254 (7)	0.0259 (7)	0.0019 (6)	0.0050 (6)	0.0001 (6)
OW2	0.0421 (10)	0.0408 (9)	0.0371 (9)	−0.0030 (8)	−0.0012 (7)	0.0031 (7)
O1	0.0317 (7)	0.0356 (7)	0.0222 (6)	−0.0068 (6)	−0.0024 (6)	0.0028 (5)
O2	0.0248 (7)	0.0421 (8)	0.0303 (7)	−0.0011 (6)	0.0063 (6)	−0.0038 (6)
O3	0.0453 (8)	0.0236 (6)	0.0216 (6)	−0.0048 (6)	0.0072 (6)	−0.0033 (5)
O4	0.0406 (8)	0.0232 (6)	0.0269 (7)	−0.0125 (6)	0.0036 (6)	0.0004 (5)
O5	0.0279 (7)	0.0163 (6)	0.0267 (6)	0.0007 (5)	0.0009 (5)	−0.0029 (5)
O6	0.0256 (6)	0.0211 (6)	0.0242 (6)	0.0014 (5)	−0.0053 (5)	0.0007 (5)
C1	0.0202 (9)	0.0250 (9)	0.0231 (9)	0.0035 (7)	0.0005 (7)	0.0001 (7)
C2	0.0250 (9)	0.0179 (8)	0.0235 (8)	−0.0006 (7)	0.0033 (7)	−0.0041 (6)
C3	0.0246 (8)	0.0154 (7)	0.0204 (8)	−0.0023 (7)	0.0038 (7)	0.0004 (6)
C4	0.0217 (8)	0.0166 (8)	0.0232 (8)	0.0010 (6)	0.0014 (7)	0.0002 (6)
C5	0.0242 (9)	0.0135 (7)	0.0230 (8)	0.0007 (6)	−0.0013 (7)	0.0011 (6)
C6	0.0159 (7)	0.0164 (7)	0.0241 (8)	−0.0029 (6)	0.0002 (6)	−0.0013 (6)

Geometric parameters (Å, º)

Na1—O3	2.3450 (15)	OW1—Na1^i	2.4271 (18)
Na1—OW1	2.3778 (16)	OW2—Na1^ii	2.561 (2)
Na1—OW1^i	2.4271 (18)	O1—C2	1.253 (2)
Na1—O1	2.4362 (16)	O2—C2	1.249 (2)
Na1—OW2	2.4712 (18)	O3—C4	1.246 (2)
Na1—OW2^ii	2.561 (2)	O4—C4	1.254 (2)
Na1—Na1^i	3.4552 (17)	O5—C6	1.318 (2)
Na1—Na1^ii	3.5179 (17)	O6—C6	1.208 (2)
N1—C5	1.496 (2)	C1—C2	1.532 (2)
N1—C3	1.501 (2)	C3—C4	1.524 (2)
N1—C1	1.505 (2)	C5—C6	1.511 (2)
O3—Na1—OW1	92.86 (6)	O1—Na1—Na1^ii	97.03 (5)
O3—Na1—OW1^i	83.74 (6)	OW2—Na1—Na1^ii	46.70 (4)
OW1—Na1—OW1^i	88.04 (6)	OW2^ii—Na1—Na1^ii	44.61 (4)
O3—Na1—O1	88.35 (5)	Na1^i—Na1—Na1^ii	114.42 (4)
OW1—Na1—O1	175.53 (6)	C5—N1—C3	113.02 (13)
OW1^i—Na1—O1	87.81 (6)	C5—N1—C1	112.22 (13)
O3—Na1—OW2	168.83 (7)	C3—N1—C1	114.09 (13)
OW1—Na1—OW2	81.89 (6)	Na1—OW1—Na1^i	91.96 (6)
OW1^i—Na1—OW2	86.22 (6)	Na1—OW2—Na1^ii	88.69 (6)
O1—Na1—OW2	96.17 (6)	C2—O1—Na1	115.32 (12)
O3—Na1—OW2^ii	98.61 (6)	C4—O3—Na1	163.21 (13)
OW1—Na1—OW2^ii	90.38 (6)	N1—C1—C2	109.94 (14)
OW1^i—Na1—OW2^ii	177.24 (6)	O2—C2—O1	127.10 (17)
O1—Na1—OW2^ii	93.69 (6)	O2—C2—C1	116.57 (16)
OW2—Na1—OW2^ii	91.31 (6)	O1—C2—C1	116.28 (16)
O3—Na1—Na1^i	87.58 (5)	N1—C3—C4	111.45 (13)
OW1—Na1—Na1^i	44.59 (4)	O3—C4—O4	125.98 (16)
OW1^i—Na1—Na1^i	43.45 (4)	O3—C4—C3	119.19 (15)
O1—Na1—Na1^i	131.24 (5)	O4—C4—C3	114.83 (14)
OW2—Na1—Na1^i	81.75 (5)	N1—C5—C6	111.92 (13)
OW2^ii—Na1—Na1^i	134.93 (6)	O6—C6—O5	124.90 (16)
O3—Na1—Na1^ii	142.95 (6)	O6—C6—C5	123.34 (15)
OW1—Na1—Na1^ii	84.59 (5)	O5—C6—C5	111.76 (14)
OW1^i—Na1—Na1^ii	132.91 (5)

Symmetry codes: (i) −x, −y+1, −z; (ii) −x+1, −y+1, −z.