Enoxacin hydro­iodide

The title compound, C₁₅H₁₈FN₄O₃⁺·I⁻, forms ionic crystals consisting of protonated enoxacin cations, C₁₅H₁₈FN₄O₃⁺, and I⁻ anions. The naphthyridine system of the cation is essentially planar, whereas the piperazine ring has a chair conformation; the enoxacin is protonated at the unsubstituted N atom of the piperazine ring. The carboxyl OH group forms an intramolecular hydrogen bond with the carbonyl O atom of the naphthyridine system, thus forming a six-membered pseudo-ring. The crystal packing is stabilized by π–π stacking of the naphthyridine rings and intermolecular hydrogen bonding involving the piperazine N—H group, the carboxyl group of the cation and the I⁻ anion, linking the residues of the structure into infinite chains running along the diagonal of the ac plane.

Key indicators

• Single-crystal X-ray study
• T = 193 K
• Mean [sigma](C-C) = 0.005 Å
• R factor = 0.042
• wR factor = 0.078
• Data-to-parameter ratio = 16.5

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Computing details

Data collection: CrsytalClear (Rigaku, 1999); cell refinement: CrystalClear; data reduction: CrystalStructure (Rigaku and Rigaku/MSC, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Siemens, 1994); software used to prepare material for publication: SHELXTL.

(I)

Crystal data

C15H18FN4O3^+·I^−	Z = 2
Mr = 448.23	F(000) = 444
Triclinic, P1	Dx = 1.789 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71070 Å
a = 6.9831 (17) Å	Cell parameters from 3760 reflections
b = 10.235 (3) Å	θ = 3.2–27.5°
c = 11.931 (3) Å	µ = 1.96 mm^−1
α = 82.783 (11)°	T = 193 K
β = 79.961 (11)°	Irregular, light yellow
γ = 85.934 (12)°	0.20 × 0.11 × 0.07 mm
V = 832.0 (4) Å^3

Data collection

Rigaku Mercury CCD diffractometer	3753 independent reflections
Radiation source: fine-focus sealed tube	3401 reflections with I > 2σ(I)'
Graphite monochromator	Rint = 0.037
Detector resolution: 7.31 pixels mm^-1	θmax = 27.5°, θmin = 3.2°
ω scans	h = −7→9
Absorption correction: multi-scan (Jacobson, 1998)	k = −13→13
Tmin = 0.696, Tmax = 0.875	l = −15→14
9442 measured reflections

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)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.078	H atoms treated by a mixture of independent and constrained refinement
S = 1.18	w = 1/[σ^2(Fo^2) + (0.0167P)^2 + 1.7702P] where P = (Fo^2 + 2Fc^2)/3
3753 reflections	(Δ/σ)max < 0.001
227 parameters	Δρmax = 0.55 e Å^−3
0 restraints	Δρmin = −0.64 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
I1	0.70806 (4)	0.55328 (3)	0.77263 (2)	0.02814 (9)
F1	0.6576 (3)	0.9896 (3)	0.77860 (19)	0.0351 (6)
O1	0.9380 (4)	0.9109 (3)	0.3722 (2)	0.0274 (6)
O2	0.9727 (4)	0.8435 (3)	0.1801 (2)	0.0333 (7)
H2	0.9938	0.8720	0.2396	0.050*
O3	0.7482 (5)	0.7337 (4)	0.1287 (3)	0.0478 (9)
N1	0.4069 (4)	0.7437 (3)	0.4558 (3)	0.0187 (6)
N2	0.3579 (4)	0.8095 (3)	0.6379 (2)	0.0181 (6)
N3	0.2833 (5)	0.8713 (3)	0.8195 (3)	0.0263 (7)
N4	0.1901 (6)	0.6841 (4)	1.0144 (3)	0.0296 (8)
C2	0.5152 (5)	0.7386 (4)	0.3518 (3)	0.0212 (8)
H1	0.4663	0.6948	0.2979	0.025*
C3	0.6934 (5)	0.7937 (4)	0.3192 (3)	0.0202 (8)
C4	0.7735 (5)	0.8584 (3)	0.3988 (3)	0.0195 (7)
C9	0.6575 (5)	0.8610 (3)	0.5101 (3)	0.0184 (7)
C8	0.4758 (5)	0.8058 (3)	0.5377 (3)	0.0176 (7)
C5	0.7180 (5)	0.9236 (4)	0.5959 (3)	0.0215 (8)
H6	0.8401	0.9633	0.5825	0.026*
C6	0.5979 (6)	0.9257 (4)	0.6976 (3)	0.0226 (8)
C7	0.4142 (5)	0.8677 (3)	0.7204 (3)	0.0192 (7)
C1	0.8033 (6)	0.7866 (4)	0.2020 (3)	0.0300 (9)
C10	0.2179 (5)	0.6787 (4)	0.4870 (3)	0.0225 (8)
H10A	0.1672	0.6687	0.4163	0.027*
H10B	0.1226	0.7356	0.5330	0.027*
C11	0.2374 (6)	0.5451 (4)	0.5547 (3)	0.0261 (9)
H11A	0.3096	0.4831	0.5045	0.039*
H11B	0.1076	0.5131	0.5857	0.039*
H11C	0.3076	0.5522	0.6178	0.039*
C12	0.1057 (6)	0.7981 (4)	0.8363 (4)	0.0311 (10)
H12A	0.0722	0.7867	0.7609	0.037*
H12B	−0.0038	0.8484	0.8787	0.037*
C13	0.1354 (6)	0.6649 (4)	0.9025 (3)	0.0296 (9)
H13A	0.0140	0.6167	0.9156	0.036*
H13B	0.2398	0.6123	0.8583	0.036*
C14	0.3639 (6)	0.7647 (4)	1.0016 (4)	0.0322 (10)
H14A	0.4805	0.7163	0.9640	0.039*
H14B	0.3870	0.7810	1.0781	0.039*
C15	0.3303 (7)	0.8943 (4)	0.9304 (3)	0.0324 (10)
H15A	0.2218	0.9463	0.9718	0.039*
H15B	0.4487	0.9455	0.9178	0.039*
H4A	0.091 (9)	0.725 (6)	1.060 (5)	0.067 (18)*
H4B	0.212 (7)	0.614 (5)	1.056 (4)	0.038 (14)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.03270 (15)	0.02672 (14)	0.02515 (14)	0.00166 (10)	−0.00684 (10)	−0.00252 (10)
F1	0.0350 (14)	0.0513 (16)	0.0232 (12)	−0.0159 (12)	−0.0041 (10)	−0.0146 (11)
O1	0.0217 (14)	0.0316 (15)	0.0257 (14)	−0.0063 (11)	0.0033 (11)	0.0014 (12)
O2	0.0341 (17)	0.0388 (18)	0.0227 (15)	−0.0037 (13)	0.0083 (13)	−0.0048 (13)
O3	0.050 (2)	0.072 (3)	0.0233 (16)	−0.0148 (18)	0.0045 (15)	−0.0189 (16)
N1	0.0200 (16)	0.0184 (15)	0.0179 (15)	−0.0019 (12)	−0.0022 (12)	−0.0032 (12)
N2	0.0195 (15)	0.0184 (15)	0.0153 (15)	−0.0020 (12)	−0.0006 (12)	−0.0002 (12)
N3	0.0263 (18)	0.0333 (19)	0.0187 (16)	−0.0029 (14)	0.0001 (14)	−0.0046 (14)
N4	0.033 (2)	0.030 (2)	0.0210 (18)	0.0032 (16)	−0.0001 (16)	0.0056 (16)
C2	0.028 (2)	0.0204 (18)	0.0150 (17)	0.0034 (15)	−0.0034 (15)	−0.0019 (15)
C3	0.0229 (19)	0.0189 (18)	0.0172 (18)	0.0000 (15)	−0.0004 (15)	−0.0003 (15)
C4	0.0179 (18)	0.0167 (17)	0.0210 (18)	0.0017 (14)	0.0003 (15)	0.0020 (15)
C9	0.0202 (18)	0.0155 (17)	0.0174 (17)	0.0002 (14)	−0.0008 (14)	0.0020 (14)
C8	0.0215 (18)	0.0128 (16)	0.0176 (17)	0.0011 (14)	−0.0047 (15)	0.0026 (14)
C5	0.0219 (19)	0.0200 (18)	0.0214 (19)	−0.0041 (15)	−0.0027 (15)	0.0026 (15)
C6	0.027 (2)	0.0215 (19)	0.0200 (18)	−0.0028 (15)	−0.0041 (16)	−0.0024 (15)
C7	0.0226 (19)	0.0153 (17)	0.0182 (18)	0.0006 (14)	−0.0030 (15)	0.0023 (14)
C1	0.033 (2)	0.031 (2)	0.022 (2)	0.0030 (18)	0.0012 (18)	−0.0001 (18)
C10	0.0171 (18)	0.028 (2)	0.0231 (19)	−0.0049 (15)	−0.0014 (15)	−0.0062 (16)
C11	0.026 (2)	0.026 (2)	0.025 (2)	−0.0079 (16)	0.0001 (17)	−0.0011 (17)
C12	0.020 (2)	0.048 (3)	0.023 (2)	−0.0005 (18)	0.0017 (16)	0.0004 (19)
C13	0.025 (2)	0.039 (2)	0.025 (2)	−0.0061 (18)	−0.0011 (17)	−0.0042 (18)
C14	0.032 (2)	0.044 (3)	0.021 (2)	−0.0043 (19)	−0.0025 (17)	−0.0049 (19)
C15	0.039 (2)	0.041 (3)	0.0182 (19)	−0.011 (2)	0.0024 (18)	−0.0115 (18)

Geometric parameters (Å, º)

C1—C3	1.480 (5)	N3—C12	1.466 (5)
C2—C3	1.376 (5)	N3—C15	1.467 (5)
C3—C4	1.432 (5)	N4—C13	1.490 (5)
C4—C9	1.432 (5)	N4—C14	1.491 (6)
C5—C6	1.351 (5)	N4—H4A	0.91 (6)
C5—C9	1.411 (5)	N4—H4B	0.84 (5)
C6—C7	1.420 (5)	C2—H1	0.9500
C8—C9	1.395 (5)	C5—H6	0.9500
C10—C11	1.509 (5)	C10—H10A	0.9900
C12—C13	1.507 (6)	C10—H10B	0.9900
C14—C15	1.510 (6)	C11—H11A	0.9800
F1—C6	1.369 (4)	C11—H11B	0.9800
O1—C4	1.275 (4)	C11—H11C	0.9800
O2—C1	1.326 (5)	C12—H12A	0.9900
O2—H2	0.8400	C12—H12B	0.9900
O3—C1	1.214 (5)	C13—H13A	0.9900
N1—C2	1.340 (5)	C13—H13B	0.9900
N1—C8	1.398 (5)	C14—H14A	0.9900
N1—C10	1.488 (5)	C14—H14B	0.9900
N2—C8	1.331 (5)	C15—H15A	0.9900
N2—C7	1.339 (5)	C15—H15B	0.9900
N3—C7	1.365 (5)
C1—O2—H2	109.5	O3—C1—C3	124.6 (4)
C2—N1—C8	119.8 (3)	O2—C1—C3	115.1 (4)
C2—N1—C10	120.8 (3)	N1—C10—C11	112.1 (3)
C8—N1—C10	119.4 (3)	N1—C10—H10A	109.2
C8—N2—C7	119.4 (3)	C11—C10—H10A	109.2
C7—N3—C12	119.7 (3)	N1—C10—H10B	109.2
C7—N3—C15	125.3 (3)	C11—C10—H10B	109.2
C12—N3—C15	110.4 (3)	H10A—C10—H10B	107.9
C13—N4—C14	113.0 (3)	C10—C11—H11A	109.5
C13—N4—H4A	112 (4)	C10—C11—H11B	109.5
C14—N4—H4A	107 (4)	H11A—C11—H11B	109.5
C13—N4—H4B	115 (3)	C10—C11—H11C	109.5
C14—N4—H4B	107 (3)	H11A—C11—H11C	109.5
H4A—N4—H4B	103 (5)	H11B—C11—H11C	109.5
N1—C2—C3	123.4 (3)	N3—C12—C13	110.1 (3)
N1—C2—H1	118.3	N3—C12—H12A	109.6
C3—C2—H1	118.3	C13—C12—H12A	109.6
C2—C3—C4	119.9 (3)	N3—C12—H12B	109.6
C2—C3—C1	120.4 (3)	C13—C12—H12B	109.6
C4—C3—C1	119.7 (3)	H12A—C12—H12B	108.2
O1—C4—C3	122.0 (3)	N4—C13—C12	108.8 (3)
O1—C4—C9	122.0 (3)	N4—C13—H13A	109.9
C3—C4—C9	116.0 (3)	C12—C13—H13A	109.9
C8—C9—C5	116.7 (3)	N4—C13—H13B	109.9
C8—C9—C4	121.6 (3)	C12—C13—H13B	109.9
C5—C9—C4	121.7 (3)	H13A—C13—H13B	108.3
N2—C8—C9	124.5 (3)	N4—C14—C15	109.5 (3)
N2—C8—N1	116.2 (3)	N4—C14—H14A	109.8
C9—C8—N1	119.3 (3)	C15—C14—H14A	109.8
C6—C5—C9	118.3 (3)	N4—C14—H14B	109.8
C6—C5—H6	120.9	C15—C14—H14B	109.8
C9—C5—H6	120.9	H14A—C14—H14B	108.2
C5—C6—F1	117.3 (3)	N3—C15—C14	110.3 (3)
C5—C6—C7	122.3 (3)	N3—C15—H15A	109.6
F1—C6—C7	120.4 (3)	C14—C15—H15A	109.6
N2—C7—N3	116.2 (3)	N3—C15—H15B	109.6
N2—C7—C6	118.8 (3)	C14—C15—H15B	109.6
N3—C7—C6	125.0 (3)	H15A—C15—H15B	108.1
O3—C1—O2	120.3 (4)
C8—N1—C2—C3	−1.0 (5)	C9—C5—C6—C7	−0.2 (6)
C10—N1—C2—C3	−178.2 (3)	C8—N2—C7—N3	178.1 (3)
N1—C2—C3—C4	1.2 (5)	C8—N2—C7—C6	1.0 (5)
N1—C2—C3—C1	−178.8 (3)	C12—N3—C7—N2	8.2 (5)
C2—C3—C4—O1	−179.9 (3)	C15—N3—C7—N2	161.6 (4)
C1—C3—C4—O1	0.1 (5)	C12—N3—C7—C6	−174.9 (3)
C2—C3—C4—C9	−0.1 (5)	C15—N3—C7—C6	−21.5 (6)
C1—C3—C4—C9	179.9 (3)	C5—C6—C7—N2	−0.4 (5)
O1—C4—C9—C8	178.6 (3)	F1—C6—C7—N2	178.0 (3)
C3—C4—C9—C8	−1.3 (5)	C5—C6—C7—N3	−177.2 (4)
O1—C4—C9—C5	1.0 (5)	F1—C6—C7—N3	1.2 (6)
C3—C4—C9—C5	−178.9 (3)	C2—C3—C1—O3	−0.3 (6)
C7—N2—C8—C9	−1.1 (5)	C4—C3—C1—O3	179.8 (4)
C7—N2—C8—N1	−179.9 (3)	C2—C3—C1—O2	179.7 (3)
C5—C9—C8—N2	0.5 (5)	C4—C3—C1—O2	−0.3 (5)
C4—C9—C8—N2	−177.2 (3)	C2—N1—C10—C11	98.1 (4)
C5—C9—C8—N1	179.3 (3)	C8—N1—C10—C11	−79.1 (4)
C4—C9—C8—N1	1.5 (5)	C7—N3—C12—C13	95.2 (4)
C2—N1—C8—N2	178.4 (3)	C15—N3—C12—C13	−61.9 (4)
C10—N1—C8—N2	−4.3 (5)	C14—N4—C13—C12	−55.4 (5)
C2—N1—C8—C9	−0.4 (5)	N3—C12—C13—N4	58.0 (4)
C10—N1—C8—C9	176.9 (3)	C13—N4—C14—C15	54.5 (5)
C8—C9—C5—C6	0.1 (5)	C7—N3—C15—C14	−94.9 (5)
C4—C9—C5—C6	177.8 (3)	C12—N3—C15—C14	60.6 (4)
C9—C5—C6—F1	−178.6 (3)	N4—C14—C15—N3	−55.8 (5)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O1	0.84	1.65	2.442 (4)	156
N4—H4B···I1^i	0.84 (5)	2.61 (5)	3.421 (4)	163 (4)
N4—H4A···O2^ii	0.91 (6)	2.02 (6)	2.880 (5)	156 (5)
N4—H4A···O3^ii	0.91 (6)	2.39 (6)	3.182 (5)	145 (5)

Symmetry codes: (i) −x+1, −y+1, −z+2; (ii) x−1, y, z+1.