Betainohydroxamic acid chloride

The title compound, N-hydroxy-2-(tri­methyl­ammonio)­acet­amide chloride, C₅H₁₃N₂O₂⁺·Cl⁻, has been synthesized and structurally characterized. The structure consists of betaino­hydroxamic acid cations and Cl⁻ anions linked by N—H...Cl and O—H...Cl hydrogen bonds into chains along [001]. It was found that the positive inductive effect of the charged N atom in close proximity to the hydroxamate carbonyl O atom has a negligible effect on the hydroxamic C—N bond length.

S1. Comment

Hydroxamic acids are weak organic acids with a variety of applications in extractive metallurgy, in pharmaceuticals, as food additives, etc. (Kaczka et al., 1962; Matzanke et al., 1989; Hershko et al., 1992; Rogers, 1987; Ghio et al., 1992). Their importance and applications primarily originate from their ability to form stable metal-ion binding sites (Crumbliss, 1991).

It was recently found that the rotation about the hydroxamate C—N bond in desferrioxamine B and N-methylacetoxydroxamic acid is slow enough to be measured by dynamic NMR spectroscopy at room temperature (Biruš et al., 1995, 1999). The rotation-rate constant was found to be ca 3 s⁻¹ at 298 K. On the other hand, the rotation rate for acetohydroxamic acid was too fast to be measured by dynamic ¹H or ¹³C NMR spectroscopy. The C and N substituents of the hydroxamic functionality have a major influence on the rotation rate, since they may increase or decrease the partial double-bond character of the hydroxamate C—N bond through their electron-donating or -withdrawing character. This, in turn, may cause the corresponding shortening or lengthening of the C—N bond. It seemed worthwhile to examine whether the positive inductive effect exerted by the positively charged N atom in betainohydroxamic acid would exhibit any effect on the length of the C—N bond. If the positive charges in close proximity to the carbonyl O atom are able to stabilize the enolate ion which is formed by an electrondensity shift from the hydroxamato-N free electron pair into the C—N bond, the partial double-bond character of the C—N bond would increase and shortening of that bond could possibly be observed. In the light of this interest, we present here the synthesis and crystal structure of betainohydroxamic acid chloride, (I). \sch

The structure of (I) consists of cations of betainohydroxamic acid and Cl⁻ anions. The crystal structure parameters can be compared with the crystal data reported for some other monohydroxamic acids. It appears that, within experimental error, the length of the hydroxamate C—N bond does not change upon substitution of the methyl H atom in acetohydroxamic acid hemihydrate [1.333 (6) Å; Bracher & Small, 1970] with the charged N atom in (I) [N2—C5 1.327 (1) Å]. Some other bond distances in (I) can also be compared with the analogous bond distances in acetohydroxamic and salicylohydroxamic acid (Larsen, 1978). For instance, the C═O bond in the betainohydroxamic acid cation [1.225 (1) Å] is slightly shorter then the corresponding one in acetohydroxamic acid [1.245 (6) Å] and salicylohydroxamic acid [1.258 (4) Å], since this O atom is not involved in hydrogen bonding in (I), whereas in the other two structures it is an acceptor for two hydrogen bonds. The N—O distances in betaino-, salicylo- and acetohydroxamic acids all appear to be equal within the range of experimental error [1.395 (1), 1.390 (4) and 1.400 (5) Å, respectively].

It seems that the positive inductive effect of the charged N atom in close proximity to the hydroxamate carbonyl O atom has a small effect on the hydroxamic C—N bond length. Both hydrogen-bond donor atoms, O2 and N2, are involved in hydrogen bonding with the Cl⁻ anion, linking the ions into chains along [001].

S2. Experimental

Betainohydroxamic acid chloride was prepared according to the published procedure of Biruš et al. (1984). Its purity was confirmed by ¹H NMR spectroscopy and by titration with a standardized solution of NaOH. Single crystals of (I) were grown from a saturated solution of betainohydroxamic acid chloride in ethanol, by slow evaporation in a thermostatic oven at 310 K. The beaker containing the solution was covered with aluminium foil to reduce evaporation. Crystals of (I) of good quality were obtained after two weeks, and these were stable for months when exposed to the atmosphere.

S3. Refinement

H atoms were found in the difference Fourier map and were refined isotropically, giving C—H distances in the range 0.87 (1)–0.99 (1) Å.

Computing details

Data collection: STADI4 (Stoe & Cie, 1995); cell refinement: X-RED (Stoe & Cie, 1995); data reduction: X-RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON98 (Spek, 1990); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of (I) with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. The packing of the ions in the unit cell of (I). Hydrogen bonds are shown by dashed lines.

N-hydroxy-2-(trimethylammonio)acetamide chloride

Crystal data

C5H13N2O2^+·Cl^−	F(000) = 360
Mr = 168.62	Dx = 1.345 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 45 reflections
a = 9.1099 (9) Å	θ = 10.0–17.7°
b = 8.8472 (13) Å	µ = 0.41 mm^−1
c = 11.0093 (11) Å	T = 295 K
β = 110.182 (6)°	Block, colourless
V = 832.84 (17) Å^3	0.45 × 0.23 × 0.17 mm
Z = 4

Data collection

Philips PW1100 updated by Stoe diffractometer	Rint = 0.045
Radiation source: Sealed X-ray tube	θmax = 30.0°, θmin = 3.0°
Planar graphite monochromator	h = −12→12
θ/2θ scans	k = −12→12
4778 measured reflections	l = −15→15
2389 independent reflections	4 standard reflections every 90 min
1324 reflections with I > 2σ(I)	intensity decay: 2.3%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.029	All H-atom parameters refined
wR(F^2) = 0.082	w = 1/[σ^2(Fo^2) + (0.0457P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.00	(Δ/σ)max < 0.001
2389 reflections	Δρmax = 0.27 e Å^−3
144 parameters	Δρmin = −0.26 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.009 (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
Cl	0.14356 (3)	0.19178 (4)	0.09396 (3)	0.04674 (12)
O1	0.38070 (13)	0.55751 (11)	0.26493 (10)	0.0554 (3)
O2	0.36907 (11)	0.27592 (10)	0.35688 (9)	0.0446 (2)
N1	0.24969 (9)	0.81483 (10)	0.35289 (7)	0.02815 (17)
N2	0.30866 (13)	0.40359 (11)	0.39729 (10)	0.0414 (2)
C1	0.27648 (12)	0.66598 (11)	0.42240 (9)	0.0305 (2)
C2	0.12184 (13)	0.80137 (17)	0.22272 (10)	0.0412 (3)
C3	0.19764 (15)	0.92661 (14)	0.43328 (12)	0.0408 (2)
C4	0.39706 (14)	0.87474 (15)	0.33694 (13)	0.0421 (3)
C5	0.32716 (11)	0.53833 (11)	0.35168 (9)	0.0310 (2)
H1	0.313 (2)	0.259 (2)	0.2840 (17)	0.070 (5)*
H2	0.2654 (18)	0.386 (2)	0.4519 (16)	0.058 (4)*
H11	0.3551 (17)	0.6845 (17)	0.5031 (15)	0.052 (4)*
H12	0.1883 (15)	0.6432 (16)	0.4320 (12)	0.033 (3)*
H21	0.0285 (17)	0.7775 (16)	0.2375 (13)	0.046 (3)*
H22	0.1126 (18)	0.890 (2)	0.1809 (14)	0.055 (4)*
H23	0.1496 (16)	0.731 (2)	0.1681 (15)	0.052 (4)*
H31	0.1013 (17)	0.8871 (16)	0.4397 (12)	0.041 (3)*
H32	0.1769 (17)	1.018 (2)	0.3922 (14)	0.052 (4)*
H33	0.2745 (17)	0.9297 (16)	0.5224 (13)	0.042 (3)*
H41	0.474 (2)	0.887 (2)	0.4184 (17)	0.060 (4)*
H42	0.4230 (17)	0.8067 (16)	0.2786 (15)	0.048 (4)*
H43	0.3733 (17)	0.972 (2)	0.3012 (14)	0.051 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl	0.04080 (16)	0.0593 (2)	0.03885 (15)	0.00682 (12)	0.01214 (11)	−0.00955 (12)
O1	0.0816 (7)	0.0420 (5)	0.0654 (5)	0.0050 (4)	0.0547 (5)	0.0023 (4)
O2	0.0523 (5)	0.0337 (4)	0.0411 (4)	0.0071 (3)	0.0074 (4)	−0.0029 (3)
N1	0.0287 (3)	0.0295 (4)	0.0282 (3)	−0.0027 (3)	0.0124 (3)	−0.0006 (3)
N2	0.0561 (6)	0.0308 (5)	0.0434 (5)	−0.0017 (4)	0.0249 (4)	−0.0011 (4)
C1	0.0343 (4)	0.0322 (5)	0.0282 (4)	−0.0004 (4)	0.0148 (3)	0.0022 (3)
C2	0.0362 (5)	0.0535 (7)	0.0299 (4)	0.0027 (5)	0.0063 (4)	0.0027 (5)
C3	0.0500 (6)	0.0335 (6)	0.0462 (6)	−0.0026 (5)	0.0259 (5)	−0.0066 (4)
C4	0.0379 (5)	0.0406 (6)	0.0547 (6)	−0.0095 (5)	0.0248 (5)	0.0004 (5)
C5	0.0300 (4)	0.0317 (5)	0.0327 (4)	−0.0004 (4)	0.0126 (3)	−0.0006 (4)

Geometric parameters (Å, º)

O1—C5	1.2248 (12)	C1—H12	0.869 (13)
O2—N2	1.3949 (13)	C2—H21	0.943 (14)
O2—H1	0.803 (19)	C2—H22	0.902 (18)
N1—C1	1.5001 (13)	C2—H23	0.957 (16)
N1—C2	1.5076 (12)	C3—H31	0.970 (15)
N1—C3	1.5085 (13)	C3—H32	0.917 (18)
N1—C4	1.5090 (12)	C3—H33	0.990 (14)
N2—C5	1.3266 (14)	C4—H41	0.934 (18)
N2—H2	0.839 (17)	C4—H42	0.967 (15)
C1—C5	1.5306 (14)	C4—H43	0.942 (19)
C1—H11	0.943 (16)
N2—O2—H1	106.8 (15)	N1—C2—H23	111.3 (8)
C1—N1—C2	110.61 (8)	H21—C2—H23	114.4 (13)
C1—N1—C3	107.76 (8)	H22—C2—H23	104.1 (14)
C2—N1—C3	108.26 (9)	N1—C3—H31	106.4 (8)
C1—N1—C4	111.90 (8)	N1—C3—H32	110.2 (9)
C2—N1—C4	110.10 (8)	H31—C3—H32	108.5 (13)
C3—N1—C4	108.08 (9)	N1—C3—H33	110.0 (8)
C5—N2—O2	119.42 (9)	H31—C3—H33	106.6 (11)
C5—N2—H2	126.0 (13)	H32—C3—H33	114.7 (13)
O2—N2—H2	114.6 (13)	N1—C4—H41	109.3 (10)
N1—C1—C5	114.38 (8)	N1—C4—H42	106.8 (9)
N1—C1—H11	105.3 (9)	H41—C4—H42	115.6 (14)
C5—C1—H11	110.1 (9)	N1—C4—H43	106.5 (9)
N1—C1—H12	105.7 (9)	H41—C4—H43	106.7 (14)
C5—C1—H12	110.2 (9)	H42—C4—H43	111.5 (13)
H11—C1—H12	111.0 (12)	O1—C5—N2	123.81 (10)
N1—C2—H21	107.5 (8)	O1—C5—C1	124.44 (9)
N1—C2—H22	108.8 (10)	N2—C5—C1	111.75 (8)
H21—C2—H22	110.7 (13)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H1···Cl	0.803 (18)	2.210 (18)	3.0083 (11)	172.8 (19)
N2—H2···Cl^i	0.839 (17)	2.313 (17)	3.1479 (13)	173.2 (12)

Symmetry code: (i) x, −y+1/2, z+1/2.