Reparación integral a la víctima

Figure 2.3. A view of the molecular structure of AFZT, showing the atom-labeling scheme. The inversion centre in the middle of the molecule makes half of the molecule independent. Displacement ellipsoids are drawn at the 50% probability level and hydrogen atoms are shown as small spheres of a arbitrary radii. [Symmetry code: (i) -x, -y, -z.]

AFZT crystallizes in the monoclinic space group P21/n with 2 formula units per unit cell (Figure 2.3); AGZTH crystallizes in the monoclinic space group C 2/c with four formula units per unit cell (Figure 2.4). The bonding parameters of the 5,5’-azotetrazolate anion are in accordance with reported values of other 5,5’-azotetrazolate salts, and therefore a detailed discussion is abstained. Selected bond lengths and angles for the cations are presented in Table 2.1.32c The azidoformamidinium cation of AFZT is a member of the series of (poly)azido derivatives of the guanidinium cation, in which the amino groups are successively replaced by N3-groups finally leading to the triazidocarbonium cation.24 As mentioned above, the aminoguanidinium cation can easily be transformed to the corresponding azide. As only few structures of this kind have been reported, a more detailed discussion is presented.35 The C–N bond lengths and angles of both cations are found to be shorter (1.308(4) – 1.388(4) Å) than the bond length of a C–N single bond (1.47 Å, Table 2.1), indicating the stabilization of the cations by the formation of a delocalized π system with a weak participation of the N3-group in the case of the azidoformamidinium cation. The bond angles around the planar C atom (sum of angles 360°) in both cations are different, and for the aminoguanidinium cation they are slightly distorted. Here N6–C2–N6 is significantly larger and N6–C2–N8 and N7–C2–N8 significantly smaller than 120°. The distortion may be caused by the C2–N8 bond, which is significantly longer than the C2–N6 and C2–N7 bonds. Analysis of 177 reports on the dimension of the (NH2)2–C–NH– fragment in the Cambridge Structural Database36 reveals a mean dC–N = 1.323(1) Å for the equivalent of the present C2–N6 and C2–N7 bonds and a mean dC–N = 1.335(1) Å for the equivalent of the C2–N8 bond. The latter is in good agreement with the bond lengths given in Table 2.1, but the C2–N6 and C2–N7 bond length in the table are shorter than

the mean values from the database. This may be explained by the intramolecular interactions of H6B with N9 (N6–H6B····N9, 2.665(5) Å) and the α-effect of the N9H2 amino group, which is also consistent with a shorter C2–N7 (1.312(2) Å) bond length compared to the longer C2–N6 (1.328(3) Å) bond length.

Figure 2.4. A view of the molecular structure of AGZTH, showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level and hydrogen atoms are shown as small spheres of a arbitrary radii. [Symmetry code: (iv) 1-x, -y, 1-z; (viii) 0.5-x, 1.5-y, 1-z; (ix) –x, y, 0.5-z]

Table 2.1. Selected bond length and angles of the cations in AFZT and AGZT

AFZT AGZTH Å C2–N6 1.308(4) 1.328(3) C2–N7 1.303(4) 1.312(2) C2–N8 1.388(4) 1.341(3) N8–N9 1.255(4) 1.414(2) N9–N10 1.112(4) - ° N6–C2–N7 123.1(3) 122.2(2) N6–C2–N8 123.9(3) 118.5(2) N7–C2–N8 113.5(2) 119.3(2) C2–N8–N9 116.2(2) 118.9(2) N8–N9–N10 169.8(3) -

For the azidoformamidinium cation in AFZT, the situation is different and can be explained by the electron withdrawing effect of the azide group and the absence of intramolecular hydrogen bonds. The two almost identical C2–N6 and C2–N7 bonds lengths (1.308(4) Å and 1.303(4) Å, respectively) show that the delocalization of the π system over the molecule is restricted to the formamidinium part of the cation and indicate a weak π-interaction with the N3-group. The bond angles N6–C2–N7 and N6–C2–N8 are very similar (~ 123°) and greater than the N7–C2–N8 angle (~ 113°). The azido group is rotated out of the molecular plane by approximately 6° (C2–N6–N7–N8). The N–N bond lengths are in agreement with those found in other azides which are covalently bound to carbon.37

Table 2.2. Hydrogen bond geometry (Å, °) of AFZT and AGZTH. D–H····A D–H H····A D····A D–H····A

AFZT N6–H6A····N3 0.86 2.1706(5) 2.9976(5) 161.230(9) N6–H6B····N5i 0.86 2.1358(5) 2.9633(6) 161.313(8) N7–H7A····N4 0.86 2.0600(4) 2.9037(5) 166.69(1) N7–H7B····N2ii 0.86 2.0688(4) 2.9120(6) 166.511(8) AGZTH O1–H1····N3 0.97(3) 1.88(3) 2.842(2) 172(3) N8–H8····O1iii 0.89(2) 2.07(2) 2.884(2) 152(2) N6–H6B····N9a 0.90(2) 2.29(2) 2.665(3) 105(2) N6–H6A····N1 0.82(3) 2.40(3) 3.201(2) 165(3) N6–H6B····N9iv _{0.90(2) 2.43(2) 3.247(3) 151(3)} N7–H7A····N5 0.87(3) 2.07(3) 2.933(3) 170(2) N7–H7B····N4v 0.89(2) 2.05(2) 2.944(2) 179(3) N9–H9A····N8vi 0.90(3) 2.49(3) 3.288(2) 148(2) N9–H9B····N2vii 0.90(3) 2.29(2) 3.156(3) 162(2) a _{intramolecular hydrogen bond;}

Symmetry codes for AFZT: (i) 0.5+x, -0.5-y, 0.5+z; (ii) -0.5+x, -0.5-y, 0.5+z; AGZTH: (iii) 0.5-x, 1.5+y, 0.5-z; (iv) 1-x, -y, 1-z; (v) 0.5-x, -0.5+y, 0.5-z; (vi) 1-x, 1-y, 1-z ; (vii) -0.5+x, 0.5+y, z.

The analysis of the crystal packing in AFZT and AGZTH shows the existence of numerous N–H····N hydrogen bonds, which are well within the sum of the van der Waals radii of two nitrogen atom (rA(N) + rD(N) = 3.10 Å).38 The N–H–N bond angles indicate a strongly directional rather than a purely electrostatic interaction (Table 2.2). In AFZT, the hydrogen atoms H7A on N7 and H7B on N6 form two intermolecular N6–H6A····N3and N7–H7A····N4 hydrogen bonds with the external nitrogen atoms (N3, N4) of the 5,5’-azotetrazolate anion,

formalism of graph-set analysis of hydrogen-bond patterns39 of the cation/anion pairs is characterized as 2(7)

2

R graph set. The center of the molecular unit contains the inversion centre. Together with two further hydrogen bonds, N6–H6B····N5i and N7–H7B····N2ii, a three- dimensional supramolecular network is formed [symmetry code: (i) 0.5+x, -0.5-y, 0.5+z; (ii) - 0.5+x, -0.5-y, 0.5+z]. The hydrogen bond network of AGZTH is more complicated. The two main graph sets are characterized as 2(10)

2

R and )2(9 2

R (Figure 2.4), forming strands which are connected to a three-dimensional network by the water molecule and the amino group (N9H2).