There are two symmetry-independent formula units of the title compound, C
6H
15N
4O
2+·F
−·HF, per cell. Both cations have a zwitterionic form, protonated at both the guanidyl and amino groups. The two symmetry-independent cations differ in their conformation. In one of them the C
γ atom is in a
gauche position to both the amino and carboxyl groups, while in the other this atom is
trans to the amino group. The two anions have very similar geometry. The F
− ions are strongly hydrogen bonded to an HF molecule [F—H
F 2.233 (2) and 2.248 (3) Å], thereby forming an asymmetric non-linear bifluoride anion. These F
F distances are the shortest reported for an asymmetric HF
2− anion.
Supporting information
CCDC reference: 140969
Crystals of (I) were prepared by reacting fluoric acid (40%, Merck) with a dilute aqueous solution of L-arginine (98% purity, Aldrich). Transparent, good quality single crystals grew from the solution by slow evaporation at room temperature over several weeks.
All H atoms could be located in a difference Fourier map at an intermediate stage of the refinement. The coordinates of the H atoms of the anion were refined freely with an isotropic displacement parameter U(H)eq = 1.5Ueq of the parent F atom. The other H atoms were placed at calculated positions and refined as riding using the SHELXL97 (Sheldrick, 1997a) defaults. Examination of the crystal structure with PLATON (Spek, 1995) showed that there are no solvent-accessible voids in the crystal lattice.
Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: HELENA (Spek, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997b); program(s) used to refine structure: SHELXL97; molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.
L-argininium fluoride hydrogen fluoride
top
Crystal data top
C6H15N4O2+·F−·HF | Z = 2 |
Mr = 214.23 | F(000) = 228 |
Triclinic, P1 | Dx = 1.454 Mg m−3 |
a = 5.1813 (11) Å | Mo Kα radiation, λ = 0.71073 Å |
b = 9.2173 (18) Å | Cell parameters from 25 reflections |
c = 10.6278 (17) Å | θ = 8.3–16.5° |
α = 87.878 (14)° | µ = 0.13 mm−1 |
β = 74.948 (16)° | T = 293 K |
γ = 86.653 (17)° | Irregular, colourless |
V = 489.18 (16) Å3 | 0.39 × 0.24 × 0.24 mm |
Data collection top
Enraf-Nonius CAD-4 diffractometer | Rint = 0.057 |
Radiation source: fine-focus sealed tube | θmax = 27.5°, θmin = 3.0° |
Graphite monochromator | h = −6→6 |
profile data from ω–2θ scans | k = −11→11 |
3023 measured reflections | l = −12→13 |
3004 independent reflections | 3 standard reflections every 180 min |
2635 reflections with I > 2σ(I) | intensity decay: 1% |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.034 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.094 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.09 | w = 1/[σ2(Fo2) + (0.0451P)2 + 0.1464P] where P = (Fo2 + 2Fc2)/3 |
3004 reflections | (Δ/σ)max < 0.001 |
261 parameters | Δρmax = 0.20 e Å−3 |
3 restraints | Δρmin = −0.19 e Å−3 |
Crystal data top
C6H15N4O2+·F−·HF | γ = 86.653 (17)° |
Mr = 214.23 | V = 489.18 (16) Å3 |
Triclinic, P1 | Z = 2 |
a = 5.1813 (11) Å | Mo Kα radiation |
b = 9.2173 (18) Å | µ = 0.13 mm−1 |
c = 10.6278 (17) Å | T = 293 K |
α = 87.878 (14)° | 0.39 × 0.24 × 0.24 mm |
β = 74.948 (16)° | |
Data collection top
Enraf-Nonius CAD-4 diffractometer | Rint = 0.057 |
3023 measured reflections | 3 standard reflections every 180 min |
3004 independent reflections | intensity decay: 1% |
2635 reflections with I > 2σ(I) | |
Refinement top
R[F2 > 2σ(F2)] = 0.034 | 3 restraints |
wR(F2) = 0.094 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.09 | Δρmax = 0.20 e Å−3 |
3004 reflections | Δρmin = −0.19 e Å−3 |
261 parameters | |
Special details top
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. The structure was solved by direct methods using SHELXS97. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
O1A | 0.7748 (3) | 0.7173 (2) | 0.51470 (17) | 0.0326 (4) | |
O2A | 0.3856 (3) | 0.65527 (19) | 0.48602 (17) | 0.0305 (4) | |
N1A | −0.0683 (5) | 0.7171 (3) | 1.2222 (2) | 0.0426 (6) | |
H1A1 | 0.0683 | 0.7663 | 1.1857 | 0.051* | |
H1A2 | −0.1227 | 0.7116 | 1.3058 | 0.051* | |
N2A | −0.3999 (5) | 0.5710 (3) | 1.2081 (2) | 0.0432 (6) | |
H2A1 | −0.4500 | 0.5638 | 1.2918 | 0.052* | |
H2A2 | −0.4832 | 0.5270 | 1.1617 | 0.052* | |
N3A | −0.1112 (5) | 0.6584 (3) | 1.0217 (2) | 0.0360 (5) | |
H3A | −0.1898 | 0.6092 | 0.9767 | 0.043* | |
N4A | 0.1506 (4) | 0.9178 (2) | 0.55354 (18) | 0.0262 (4) | |
H4A1 | 0.0595 | 0.9892 | 0.6029 | 0.039* | |
H4A2 | 0.0494 | 0.8415 | 0.5618 | 0.039* | |
H4A3 | 0.1955 | 0.9480 | 0.4706 | 0.039* | |
C1A | −0.1937 (5) | 0.6504 (3) | 1.1505 (2) | 0.0327 (5) | |
C2A | 0.1070 (5) | 0.7471 (3) | 0.9538 (2) | 0.0316 (5) | |
H2A3 | 0.2713 | 0.7098 | 0.9737 | 0..038* | |
H2A4 | 0.0709 | 0.8459 | 0.9845 | 0.038* | |
C3A | 0.1435 (5) | 0.7479 (3) | 0.8073 (2) | 0.0315 (5) | |
H3A1 | 0.2095 | 0.6526 | 0.7736 | 0.038* | |
H3A2 | −0.0269 | 0.7708 | 0.7874 | 0.038* | |
C4A | 0.3413 (5) | 0.8604 (3) | 0.7439 (2) | 0.0282 (5) | |
H4A4 | 0.5092 | 0.8361 | 0.7659 | 0.034* | |
H4A5 | 0.2744 | 0.9541 | 0.7810 | 0.034* | |
C5A | 0.3971 (4) | 0.8754 (2) | 0.5959 (2) | 0.0235 (4) | |
H5A | 0.5222 | 0.9530 | 0.5672 | 0.028* | |
C6A | 0.5280 (4) | 0.7366 (2) | 0.52628 (19) | 0.0234 (4) | |
O2B | 0.8257 (3) | 0.15423 (18) | 0.68154 (15) | 0.0280 (4) | |
O1B | 0.4325 (3) | 0.2384 (2) | 0.65343 (18) | 0.0364 (4) | |
N2B | 1.0601 (5) | 0.2258 (3) | −0.0692 (2) | 0.0401 (5) | |
H2B1 | 1.1565 | 0.2756 | −0.0337 | 0.048* | |
H2B2 | 1.0938 | 0.2228 | −0.1527 | 0.048* | |
N1B | 0.7157 (5) | 0.0756 (3) | −0.0507 (2) | 0.0412 (5) | |
H1B1 | 0.7518 | 0.0717 | −0.1343 | 0.049* | |
H1B2 | 0.5855 | 0.0287 | −0.0031 | 0.049* | |
N3B | 0.8073 (4) | 0.1580 (3) | 0.13288 (18) | 0.0342 (5) | |
H3B | 0.6741 | 0.1111 | 0.1780 | 0.041* | |
N4B | 1.0017 (4) | 0.4356 (2) | 0.62012 (18) | 0.0264 (4) | |
H4B1 | 1.0752 | 0.5119 | 0.5734 | 0.040* | |
H4B2 | 1.1297 | 0.3697 | 0.6276 | 0.040* | |
H4B3 | 0.9103 | 0.4642 | 0.6990 | 0.040* | |
C1B | 0.8606 (5) | 0.1541 (3) | 0.0044 (2) | 0.0312 (5) | |
C2B | 0.9606 (5) | 0.2370 (3) | 0.2026 (2) | 0.0329 (5) | |
H2B3 | 0.9859 | 0.3346 | 0.1658 | 0.039* | |
H2B4 | 1.1356 | 0.1884 | 0.1930 | 0.039* | |
C3B | 0.8149 (5) | 0.2443 (3) | 0.3456 (2) | 0.0321 (5) | |
H3B1 | 0.7846 | 0.1467 | 0.3817 | 0.039* | |
H3B2 | 0.6423 | 0.2957 | 0.3553 | 0.039* | |
C4B | 0.9801 (5) | 0.3228 (3) | 0.4194 (2) | 0.0299 (5) | |
H4B4 | 1.1293 | 0.2587 | 0.4290 | 0.036* | |
H4B5 | 1.0526 | 0.4076 | 0.3686 | 0.036* | |
C5B | 0.8170 (4) | 0.3704 (2) | 0.5536 (2) | 0.0233 (4) | |
H5B | 0.6805 | 0.4447 | 0.5431 | 0.028* | |
C6B | 0.6787 (4) | 0.2441 (2) | 0.63743 (19) | 0.0224 (4) | |
F1 | 0.4016 (4) | 0.4155 (2) | 1.0185 (2) | 0.0615 (5) | |
H1 | 0.508 (11) | 0.453 (6) | 0.931 (5) | 0.092* | |
F2 | 0.3956 (4) | 1.0056 (2) | 0.31635 (16) | 0.0576 (5) | |
H2 | 0.360 (10) | 0.944 (5) | 0.242 (5) | 0.086* | |
F3 | 0.6689 (4) | 0.5215 (2) | 0.84223 (17) | 0.0548 (5) | |
F4 | 0.3551 (5) | 0.9060 (3) | 0.13452 (18) | 0.0697 (7) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
O1A | 0.0207 (8) | 0.0343 (9) | 0.0412 (9) | −0.0009 (7) | −0.0045 (7) | −0.0040 (7) |
O2A | 0.0269 (9) | 0.0285 (9) | 0.0349 (8) | −0.0039 (7) | −0.0043 (7) | −0.0068 (6) |
N1A | 0.0429 (13) | 0.0567 (15) | 0.0238 (10) | −0.0128 (12) | 0.0016 (9) | −0.0015 (10) |
N2A | 0.0427 (14) | 0.0509 (14) | 0.0307 (10) | −0.0130 (11) | 0.0024 (9) | 0.0004 (10) |
N3A | 0.0358 (12) | 0.0455 (13) | 0.0254 (10) | −0.0097 (10) | −0.0036 (9) | −0.0035 (9) |
N4A | 0.0273 (10) | 0.0228 (9) | 0.0269 (9) | 0.0013 (7) | −0.0045 (7) | −0.0012 (7) |
C1A | 0.0337 (13) | 0.0347 (13) | 0.0261 (11) | 0.0026 (10) | −0.0021 (10) | −0.0012 (9) |
C2A | 0.0325 (13) | 0.0373 (14) | 0.0221 (10) | −0.0015 (10) | −0.0020 (9) | −0.0023 (9) |
C3A | 0.0314 (12) | 0.0405 (14) | 0.0216 (10) | −0.0078 (11) | −0.0039 (9) | −0.0004 (9) |
C4A | 0.0283 (12) | 0.0330 (13) | 0.0235 (10) | −0.0037 (10) | −0.0055 (9) | −0.0072 (9) |
C5A | 0.0211 (10) | 0.0226 (11) | 0.0255 (10) | −0.0032 (8) | −0.0028 (8) | −0.0015 (8) |
C6A | 0.0224 (11) | 0.0236 (11) | 0.0215 (9) | −0.0030 (8) | −0.0009 (8) | 0.0022 (8) |
O2B | 0.0276 (8) | 0.0270 (8) | 0.0277 (8) | 0.0006 (7) | −0.0046 (6) | 0.0031 (6) |
O1B | 0.0215 (9) | 0.0409 (10) | 0.0452 (9) | −0.0070 (7) | −0.0058 (7) | 0.0086 (8) |
N2B | 0.0475 (14) | 0.0487 (14) | 0.0206 (9) | −0.0110 (11) | −0.0008 (9) | 0.0010 (9) |
N1B | 0.0500 (15) | 0.0492 (14) | 0.0264 (10) | −0.0081 (11) | −0.0117 (10) | −0.0036 (9) |
N3B | 0.0354 (12) | 0.0459 (13) | 0.0210 (9) | −0.0129 (10) | −0.0046 (8) | −0.0004 (8) |
N4B | 0.0268 (10) | 0.0240 (9) | 0.0274 (9) | −0.0067 (8) | −0.0038 (8) | −0.0024 (7) |
C1B | 0.0357 (14) | 0.0327 (13) | 0.0236 (11) | 0.0029 (10) | −0.0056 (10) | −0.0023 (9) |
C2B | 0.0324 (13) | 0.0420 (14) | 0.0237 (11) | −0.0086 (11) | −0.0047 (9) | −0.0013 (10) |
C3B | 0.0324 (12) | 0.0426 (14) | 0.0218 (11) | −0.0126 (11) | −0.0055 (9) | −0.0022 (9) |
C4B | 0.0274 (11) | 0.0374 (13) | 0.0231 (10) | −0.0140 (10) | −0.0011 (9) | 0.0010 (9) |
C5B | 0.0221 (11) | 0.0230 (11) | 0.0249 (10) | −0.0034 (8) | −0.0059 (8) | 0.0009 (8) |
C6B | 0.0210 (11) | 0.0259 (11) | 0.0186 (9) | −0.0049 (8) | −0.0009 (8) | −0.0026 (8) |
F1 | 0.0600 (13) | 0.0680 (13) | 0.0501 (10) | −0.0285 (11) | 0.0023 (9) | 0.0019 (9) |
F2 | 0.0731 (14) | 0.0677 (12) | 0.0318 (8) | −0.0337 (10) | −0.0072 (8) | 0.0020 (8) |
F3 | 0.0528 (11) | 0.0612 (12) | 0.0410 (8) | −0.0156 (9) | 0.0092 (8) | −0.0115 (8) |
F4 | 0.0895 (17) | 0.0802 (15) | 0.0409 (9) | −0.0427 (13) | −0.0103 (10) | −0.0071 (9) |
Geometric parameters (Å, º) top
O1A—C6A | 1.255 (3) | N2B—C1B | 1.319 (4) |
O2A—C6A | 1.242 (3) | N2B—H2B1 | 0.8600 |
N1A—C1A | 1.311 (4) | N2B—H2B2 | 0.8600 |
N1A—H1A1 | 0.8600 | N1B—C1B | 1.324 (4) |
N1A—H1A2 | 0.8600 | N1B—H1B1 | 0.8600 |
N2A—C1A | 1.331 (4) | N1B—H1B2 | 0.8600 |
N2A—H2A1 | 0.8600 | N3B—C1B | 1.322 (3) |
N2A—H2A2 | 0.8600 | N3B—C2B | 1.457 (3) |
N3A—C1A | 1.325 (3) | N3B—H3B | 0.8600 |
N3A—C2A | 1.452 (3) | N4B—C5B | 1.492 (3) |
N3A—H3A | 0.8600 | N4B—H4B1 | 0.8900 |
N4A—C5A | 1.488 (3) | N4B—H4B2 | 0.8900 |
N4A—H4A1 | 0.8900 | N4B—H4B3 | 0.8900 |
N4A—H4A2 | 0.8900 | C2B—C3B | 1.513 (3) |
N4A—H4A3 | 0.8900 | C2B—H2B3 | 0.9700 |
C2A—C3A | 1.519 (3) | C2B—H2B4 | 0.9700 |
C2A—H2A3 | 0.9700 | C3B—C4B | 1.527 (3) |
C2A—H2A4 | 0.9700 | C3B—H3B1 | 0.9700 |
C3A—C4A | 1.515 (3) | C3B—H3B2 | 0.9700 |
C3A—H3A1 | 0.9700 | C4B—C5B | 1.523 (3) |
C3A—H3A2 | 0.9700 | C4B—H4B4 | 0.9700 |
C4A—C5A | 1.526 (3) | C4B—H4B5 | 0.9700 |
C4A—H4A4 | 0.9700 | C5B—C6B | 1.533 (3) |
C4A—H4A5 | 0.9700 | C5B—H5B | 0.9800 |
C5A—C6A | 1.533 (3) | F1—H1 | 1.01 (6) |
C5A—H5A | 0.9800 | F2—H2 | 1.04 (6) |
O2B—C6B | 1.252 (3) | F3—H1 | 1.26 (6) |
O1B—C6B | 1.246 (3) | F4—H2 | 1.22 (5) |
| | | |
C1A—N1A—H1A1 | 120.0 | C1B—N2B—H2B1 | 120.0 |
C1A—N1A—H1A2 | 120.0 | C1B—N2B—H2B2 | 120.0 |
H1A1—N1A—H1A2 | 120.0 | H2B1—N2B—H2B2 | 120.0 |
C1A—N2A—H2A1 | 120.0 | C1B—N1B—H1B1 | 120.0 |
C1A—N2A—H2A2 | 120.0 | C1B—N1B—H1B2 | 120.0 |
H2A1—N2A—H2A2 | 120.0 | H1B1—N1B—H1B2 | 120.0 |
C1A—N3A—C2A | 122.4 (2) | C1B—N3B—C2B | 123.9 (2) |
C1A—N3A—H3A | 118.8 | C1B—N3B—H3B | 118.1 |
C2A—N3A—H3A | 118.8 | C2B—N3B—H3B | 118.1 |
C5A—N4A—H4A1 | 109.5 | C5B—N4B—H4B1 | 109.5 |
C5A—N4A—H4A2 | 109.5 | C5B—N4B—H4B2 | 109.5 |
H4A1—N4A—H4A2 | 109.5 | H4B1—N4B—H4B2 | 109.5 |
C5A—N4A—H4A3 | 109.5 | C5B—N4B—H4B3 | 109.5 |
H4A1—N4A—H4A3 | 109.5 | H4B1—N4B—H4B3 | 109.5 |
H4A2—N4A—H4A3 | 109.5 | H4B2—N4B—H4B3 | 109.5 |
N1A—C1A—N3A | 120.4 (2) | N2B—C1B—N3B | 120.5 (2) |
N1A—C1A—N2A | 119.5 (2) | N2B—C1B—N1B | 119.7 (2) |
N3A—C1A—N2A | 120.1 (2) | N3B—C1B—N1B | 119.8 (3) |
N3A—C2A—C3A | 111.6 (2) | N3B—C2B—C3B | 110.09 (19) |
N3A—C2A—H2A3 | 109.3 | N3B—C2B—H2B3 | 109.6 |
C3A—C2A—H2A3 | 109.3 | C3B—C2B—H2B3 | 109.6 |
N3A—C2A—H2A4 | 109.3 | N3B—C2B—H2B4 | 109.6 |
C3A—C2A—H2A4 | 109.3 | C3B—C2B—H2B4 | 109.6 |
H2A3—C2A—H2A4 | 108.0 | H2B3—C2B—H2B4 | 108.2 |
C4A—C3A—C2A | 109.1 (2) | C2B—C3B—C4B | 110.06 (19) |
C4A—C3A—H3A1 | 109.9 | C2B—C3B—H3B1 | 109.6 |
C2A—C3A—H3A1 | 109.9 | C4B—C3B—H3B1 | 109.6 |
C4A—C3A—H3A2 | 109.9 | C2B—C3B—H3B2 | 109.6 |
C2A—C3A—H3A2 | 109.9 | C4B—C3B—H3B2 | 109.6 |
H3A1—C3A—H3A2 | 108.3 | H3B1—C3B—H3B2 | 108.2 |
C3A—C4A—C5A | 115.39 (18) | C5B—C4B—C3B | 112.65 (19) |
C3A—C4A—H4A4 | 108.4 | C5B—C4B—H4B4 | 109.1 |
C5A—C4A—H4A4 | 108.4 | C3B—C4B—H4B4 | 109.1 |
C3A—C4A—H4A5 | 108.4 | C5B—C4B—H4B5 | 109.1 |
C5A—C4A—H4A5 | 108.4 | C3B—C4B—H4B5 | 109.1 |
H4A4—C4A—H4A5 | 107.5 | H4B4—C4B—H4B5 | 107.8 |
N4A—C5A—C4A | 112.03 (18) | N4B—C5B—C4B | 107.97 (18) |
N4A—C5A—C6A | 109.07 (18) | N4B—C5B—C6B | 109.59 (17) |
C4A—C5A—C6A | 112.78 (19) | C4B—C5B—C6B | 112.56 (18) |
N4A—C5A—H5A | 107.6 | N4B—C5B—H5B | 108.9 |
C4A—C5A—H5A | 107.6 | C4B—C5B—H5B | 108.9 |
C6A—C5A—H5A | 107.6 | C6B—C5B—H5B | 108.9 |
O2A—C6A—O1A | 126.1 (2) | O1B—C6B—O2B | 125.9 (2) |
O2A—C6A—C5A | 118.5 (2) | O1B—C6B—C5B | 117.4 (2) |
O1A—C6A—C5A | 115.5 (2) | O2B—C6B—C5B | 116.63 (19) |
| | | |
C2A—N3A—C1A—N1A | −4.0 (4) | C2B—N3B—C1B—N2B | −1.0 (4) |
C2A—N3A—C1A—N2A | 177.9 (2) | C2B—N3B—C1B—N1B | 177.9 (2) |
C1A—N3A—C2A—C3A | −174.6 (3) | C1B—N3B—C2B—C3B | 168.6 (3) |
N3A—C2A—C3A—C4A | 170.8 (2) | N3B—C2B—C3B—C4B | 178.2 (2) |
C2A—C3A—C4A—C5A | −179.4 (2) | C2B—C3B—C4B—C5B | 164.4 (2) |
C3A—C4A—C5A—N4A | 60.1 (3) | C3B—C4B—C5B—N4B | 175.9 (2) |
C3A—C4A—C5A—C6A | −63.4 (3) | C3B—C4B—C5B—C6B | 54.9 (3) |
N4A—C5A—C6A—O2A | −23.9 (3) | N4B—C5B—C6B—O1B | 134.1 (2) |
C4A—C5A—C6A—O2A | 101.2 (2) | C4B—C5B—C6B—O1B | −105.7 (2) |
N4A—C5A—C6A—O1A | 155.50 (18) | N4B—C5B—C6B—O2B | −47.2 (2) |
C4A—C5A—C6A—O1A | −79.3 (2) | C4B—C5B—C6B—O2B | 72.9 (2) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
F1—H1···F3 | 1.01 (6) | 1.26 (6) | 2.248 (3) | 163 (5) |
F2—H2···F4 | 1.04 (6) | 1.22 (5) | 2.233 (2) | 161 (5) |
N1A—H1A1···F4i | 0.86 | 1.98 | 2.825 (3) | 168 |
N1A—H1A2···O1Aii | 0.86 | 2.15 | 3.002 (3) | 173 |
N2A—H2A1···O2Aii | 0.86 | 2.20 | 2.987 (3) | 153 |
N2A—H2A2···F1iii | 0.86 | 2.10 | 2.939 (3) | 167 |
N3A—H3A···F3iii | 0.86 | 1.98 | 2.829 (3) | 168 |
N4A—H4A1···O2Biv | 0.89 | 1.96 | 2.835 (3) | 168 |
N4A—H4A3···F2 | 0.89 | 1.78 | 2.632 (3) | 160 |
N4A—H4A2···O1Aiii | 0.89 | 2.05 | 2.876 (3) | 155 |
N2B—H2B1···F1v | 0.86 | 2.05 | 2.897 (3) | 169 |
N2B—H2B2···O1Bv | 0.86 | 2.34 | 3.078 (3) | 144 |
N2B—H2B2···O2Bvi | 0.86 | 2.62 | 3.290 (3) | 135 |
N1B—H1B1···O2Bvi | 0.86 | 2.02 | 2.828 (3) | 156 |
N1B—H1B2···F4vii | 0.86 | 1.99 | 2.831 (3) | 165 |
N3B—H3B···F2vii | 0.86 | 2.04 | 2.883 (3) | 168 |
N4B—H4B1···O2Aviii | 0.89 | 2.14 | 2.979 (3) | 157 |
N4B—H4B1···O1A | 0.89 | 2.54 | 3.080 (3) | 120 |
N4B—H4B3···F3 | 0.89 | 1.78 | 2.652 (3) | 168 |
N4B—H4B2···O1Bviii | 0.89 | 2.00 | 2.882 (3) | 174 |
Symmetry codes: (i) x, y, z+1; (ii) x−1, y, z+1; (iii) x−1, y, z; (iv) x−1, y+1, z; (v) x+1, y, z−1; (vi) x, y, z−1; (vii) x, y−1, z; (viii) x+1, y, z. |
Experimental details
Crystal data |
Chemical formula | C6H15N4O2+·F−·HF |
Mr | 214.23 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 293 |
a, b, c (Å) | 5.1813 (11), 9.2173 (18), 10.6278 (17) |
α, β, γ (°) | 87.878 (14), 74.948 (16), 86.653 (17) |
V (Å3) | 489.18 (16) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.13 |
Crystal size (mm) | 0.39 × 0.24 × 0.24 |
|
Data collection |
Diffractometer | Enraf-Nonius CAD-4 diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3023, 3004, 2635 |
Rint | 0.057 |
(sin θ/λ)max (Å−1) | 0.649 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.034, 0.094, 1.09 |
No. of reflections | 3004 |
No. of parameters | 261 |
No. of restraints | 3 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.20, −0.19 |
Selected geometric parameters (Å, º) topO1A—C6A | 1.255 (3) | O2B—C6B | 1.252 (3) |
O2A—C6A | 1.242 (3) | O1B—C6B | 1.246 (3) |
| | | |
O2A—C6A—O1A | 126.1 (2) | O1B—C6B—O2B | 125.9 (2) |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
F1—H1···F3 | 1.01 (6) | 1.26 (6) | 2.248 (3) | 163 (5) |
F2—H2···F4 | 1.04 (6) | 1.22 (5) | 2.233 (2) | 161 (5) |
N1A—H1A1···F4i | 0.86 | 1.98 | 2.825 (3) | 168 |
N1A—H1A2···O1Aii | 0.86 | 2.15 | 3.002 (3) | 173 |
N2A—H2A1···O2Aii | 0.86 | 2.20 | 2.987 (3) | 153 |
N2A—H2A2···F1iii | 0.86 | 2.10 | 2.939 (3) | 167 |
N3A—H3A···F3iii | 0.86 | 1.98 | 2.829 (3) | 168 |
N4A—H4A1···O2Biv | 0.89 | 1.96 | 2.835 (3) | 168 |
N4A—H4A3···F2 | 0.89 | 1.78 | 2.632 (3) | 160 |
N4A—H4A2···O1Aiii | 0.89 | 2.05 | 2.876 (3) | 155 |
N2B—H2B1···F1v | 0.86 | 2.05 | 2.897 (3) | 169 |
N2B—H2B2···O1Bv | 0.86 | 2.34 | 3.078 (3) | 144 |
N2B—H2B2···O2Bvi | 0.86 | 2.62 | 3.290 (3) | 135 |
N1B—H1B1···O2Bvi | 0.86 | 2.02 | 2.828 (3) | 156 |
N1B—H1B2···F4vii | 0.86 | 1.99 | 2.831 (3) | 165 |
N3B—H3B···F2vii | 0.86 | 2.04 | 2.883 (3) | 168 |
N4B—H4B1···O2Aviii | 0.89 | 2.14 | 2.979 (3) | 157 |
N4B—H4B1···O1A | 0.89 | 2.54 | 3.080 (3) | 120 |
N4B—H4B3···F3 | 0.89 | 1.78 | 2.652 (3) | 168 |
N4B—H4B2···O1Bviii | 0.89 | 2.00 | 2.882 (3) | 174 |
Symmetry codes: (i) x, y, z+1; (ii) x−1, y, z+1; (iii) x−1, y, z; (iv) x−1, y+1, z; (v) x+1, y, z−1; (vi) x, y, z−1; (vii) x, y−1, z; (viii) x+1, y, z. |
A number of arginine salts have interesting non-linear optical properties, of which L-arginine phosphate and L-arginine fluoride have the strongest second harmonic generation signal (Monaco et al., 1987), roughly six times that of quartz or four times that of potassium dihydrogen phosphate (KDP). The radiation threshold for these compounds is relatively large, which is important for applications such as harmonic generators for lasers used in fusion experiments. L-Arginine fluoride is optically biaxial and is non-critically phase-matched, which is a valuable property for applications that require blue-green light. It crystallizes in the space group P21, but its crystal structure has not yet been published (Monaco et al., 1987). In an effort to synthesize L-arginine fluoride we have obtained the title compound, (I), which includes an additional HF molecule strongly hydrogen bonded to F−.
The HF2− anion is of significant structural and theoretical interest. It is a classic example for semi-ionic three-centre four-electron bonding (Pimentel, 1951) and exhibits the strongest known hydrogen bond (Williams & Schneemeyer, 1973) which, depending on the symmetry of the surrounding crystal field, can be either symmetric or asymmetric (Lautie et al., 1984). Typical dissociation energies reported for the bifluoride anion exceed 24 kcal/mol.
Both symmetry-independent anions in the crystal of (I) deviate significantly from linearity and have the H atom in an off-centred position, as shown by the F—H···F angles and the F—H and H···F distances (Table 2). This geometry compares well with that established by other studies (Denne & Mackay, 1971; Whittlesey et al., 1997; Williams & Schneemeyer, 1973) but is different from the D∞h geometry of the isolated ion as given by good quality ab initio calculations using extended basis-sets (Heidrich et al., 1993). In a few salts in which the bifluoride anion is under the influence of a highly symmetrical crystal field, such as in tetramethylammonium bifluoride (Wilson et al., 1989) and alkali bifluorides (Rush et al., 1972), such a symmetric FHF− anion has been observed.
The F···F distances for the two bifluoride anions are 2.248 (3) and 2.233 (2) Å, for ions F1—H1···F3− and F2—H2···F4−, respectively. These values are considerably less than twice the van der Waals radius of fluorine (1.4 Å), as expected from a very strong hydrogen bond. These F···F distances are the shortest reported for asymmetric bifluoride anions and are only slightly larger than the absolute shortest value reported for the symmetric anion in tetramethyl ammonium bifluoride [2.213 (4) Å; Wilson et al., 1989]. The experimental value for the anionic F···F distance obtained in the gas phase from infrared diode laser spectroscopy is 2.27771 (7) Å (Kawaguchi & Hirota, 1986). There has also been much theoretical effort in ab initio calculations of the ground state geometry and vibrational properties of the bifluoride anion. For the isolated symmetric anion a range of values [2.256–2.298 Å] for the F···F distance has been reported. In a recent calculation (Heidrich et al., 1993) for the (HF)3 molecule, which may be partitioned into the two conceivable subunits FH2+ and F2H−, the bifluoride anion deviates 27.7° from the linear geometry and the F···F distance is 2.255 Å.
The two protonated arginine molecules exist as positively charged zwitterions, with both the guanidyl and amino groups protonated. Inspection of the C═O distances in the carboxyl groups (1.242–1.255 Å) show that these are deprotonated. The conformations of the amino acid cations in the two molecules A and B are best described by the torsion angles according to the rules of IUPAC-IUB (1970): ϕ1 = 155.50 (18) and 134.1 (2), ϕ2 = −23.9 (3) and −47.2 (2), χ1 = 60.1 (3) and 175.9 (2), χ2 = −179.4 (2) and 164.4 (2), χ3 = 170.8 (2) and 178.2 (2), χ4 = −174.6 (2) and −168.6 (3), χ51 = −4.0 (4) and −1.0 (4), and χ52 = 177.9 (2) and 177.9 (2)°, for molecules A and B, respectively. The two arginine molecules have different conformations, as can be seen from the internal rotation angles about the C4—C5 bond, resulting in different staggered positions of the C3 atom. In the molecule labelled A, atom C3A is found in a gauche position to both the amino and carboxyl groups, while in molecule B, atom C3B is in a trans position to the amino group.
The structure is held together by a complex three-dimensional hydrogen-bond network. Full capability for hydrogen bonding of the guanidyl and amino groups of the two argininium ions is achieved. Both F atoms of each bifluoride anion accept two protons each, besides the shared inner proton. The anions bridge the cations via hydrogen bonds involving the amino and guanidyl groups. Details of the hydrogen bonding are given in table 2.
It should be mentioned that because there is no significant anomalous dispersion by any atom in compound (I) at the Mo Kα wavelength, the enantiomorph was not determined from the X-ray data and the chirality assigned to the molecule is the well known chirality of L-arginine (the configuration of the chiral Cα atom is S). Measurements of the optical properties of this compound are under way.