2,4,6-Triamino-1,3,5-triazine–1H-isoindole-1,3(2H)-dione (1/3)

The asymmetric unit of the title compound, C₃H₆N₆·3C₈H₅NO₂, contains a melamine and a phthalimide [1H-isoindole-1,3(2H)-dione] mol­ecule, both residing on a mirror plane, and a second phthalimide mol­ecule residing on a general position. The two components are linked by almost linear N—H...O and N—H...N hydrogen bonds, forming an essentially planar superstructure. These aggregates, related by a twofold screw axis, inter­act through weak C—H...O contacts, forming chains parallel to the b axis, while those related by translation along the c axis inter­act via π–π inter­actions between the π clouds of the aromatic triazine and phthalimide rings to form a stacked structure.

S1. Comment

The present study is a continuation of our investigations into the characterization of hydrogen-bonding networks formed by triazine derivatives in the solid state (Perpétuo & Janczak, 2005; Janczak & Kubiak, 2005). Triazine and its derivatives, especially 2,4,6-triamino-1,3,5-triazine, i.e. melamine, and its organic and inorganic complexes or salts, can develop well defined noncovalent supramolecular architectures because of their ability to form multiple hydrogen bonds since they contain components of complementary arrays of hydrogen-bonding sites (Desiraju, 1990; MacDonald & Whitesides, 1994; Row, 1999; Krische & Lehn, 2000; Sherrington & Taskinen, 2001). Our interest in these materials arises from the possibility of their displaying nonlinear optical properties (Janczak & Perpétuo, 2002; Marchewka et al., 2003; Perpétuo & Janczak, 2006). We present here the 2,4,6-triamino-1,3,5-triazine–tris(phthalimide) cocrystal, (I), which contains multiple N—H···N and N—H···O hydrogen-bonding interactions.

The asymmetric unit of (I) comprises a half melamine and one and a half phthalimide molecules (Fig. 1). These units through a crystallographic mirror plane form an almost planar C₃H₆N₆·3C₈H₅NO₂ aggregate. The triazine ring in melamine is essentially planar [the deviation of the N and C atoms from the mean plane is less than 0.037 (2) Å], but exhibits significant distortion from the ideal hexagonal form (D_3h symmetry). The internal C—N—C angles are smaller than 120°, while the internal N—C—N angles are greater than 120°. This distortion results from the steric effect of the lone-pair electrons, predicted by the valence-shell electron-pair repulsion theory (Gillespie, 1963, 1992). The ab-initio gas-phase geometry calculated for an isolated melamine molecule shows similar correlation between the internal C—N—C and N—C—N angles within the ring (Drozd & Marchewka, 2005). Thus the ring distortions result mainly from the steric effect of the lone pairs of electrons on the ring N atoms and, to a lesser degree, from the hydrogen-bonding arrangement, which diminishes the steric effect of these electron lone pairs by about 2° compared with the ab-initio results (Drozd & Marchewka, 2005). The phthalimide molecule has a similar geometry to that found in the pure phthalimide crystal (Matzat, 1972; Ng, 1992; Zakaria et al., 2002).

An extensive set of almost linear hydrogen bonds (Table 1) link the components of (I) into essentially planar C₃H₆N₆·3C₈H₅NO₂ aggregates with pseudo-threefold symmetry. These aggregates related by a twofold symmetry screw axis interact via C—H···O contacts, forming chains parallel to the b axis, while the plane defined by the atoms of the C₃H₆N₆·3C₈H₅NO₂ aggregates of the chain is inclined by 27.6° to the (001) plane. Each melamine molecule is involved in a maximum of nine hydrogen bonds; in six of these it acts as a donor and in the remaining three as an acceptor (Table 1). The chains related by a translation along the c axis interact via π–π interactions between the π clouds of the aromatic triazine and the phthalimide rings forming a stacked structure. Within the stack the triazine rings are separated by ~3.27 Å and the phthalimide molecules are separated by ~3.40 Å. These values indicate relatively strong π–π interactions within the stack, since they are comparable to the value of 3.4 Å for the interacting π aromatic ring system (Pauling, 1960).

Related literature

For related literature, see: Desiraju (1990); Drozd & Marchewka (2005); Gillespie (1963, 1992); Janczak & Kubiak (2005); Janczak & Perpétuo (2002); Krische & Lehn (2000); MacDonald & Whitesides (1994); Marchewka et al. (2003); Matzat (1972); Ng (1992); Pauling (1960); Perpétuo & Janczak (2005, 2006); Row (1999); Sherrington & Taskinen (2001); Zakaria et al. (2002).

S2. Experimental

A mixture of 2,4,6-triamino-1,3,5-triazine (quality ca 98%) and phthalimide (quality > 99%) in the molar proportion of 1:3 was heated under vaccum in a sealed glass ampoule in a temperature gradient (hot zone 473 K, cold zone 373 K). After several hours, colourless crystals formed in the cold zone, which proved to be suitable for single-crystal X-ray diffraction analysis.

S3. Refinement

The H atoms were placed in their geometrically defined positions with U_iso(H) values of 1.2U_eq of the N or C atoms directly attached to the H atoms.

Computing details

Data collection: KM-4 CCD Software (Kuma, 2004); cell refinement: KM-4 CCD Software; data reduction: KM-4 CCD Softwere; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1990); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of (I) showing displacement ellipsoids at the 50% probability level and H atoms as spheres of arbitrary radii. Hydrogen bonds are drawn as dashed lines. [Symmetry code: (i) x, -y + 1/2, z.]
	Fig. 2. A view of the crystal packing in (I), showing the hydrogen bonded C3H6N6·3C8H5NO2 aggregates interacting via C—H···O hydrogen bonds to form chains along the b axis.

2,4,6-Triamino-1,3,5-triazine–1H-isoindole-1,3(2H)-dione (1/3)

Crystal data

C3H6N6·3C8H5NO2	F(000) = 1176
Mr = 567.53	Dx = 1.443 Mg m^−3 Dm = 1.44 Mg m^−3 Dm measured by floatation
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 1265 reflections
a = 26.709 (5) Å	θ = 2.0–25.7°
b = 25.884 (5) Å	µ = 0.11 mm^−1
c = 3.779 (1) Å	T = 295 K
V = 2612.6 (10) Å^3	Paralellepiped, colourless
Z = 4	0.30 × 0.28 × 0.22 mm

Data collection

Kuma KM-4 CCD diffractometer	2555 independent reflections
Radiation source: fine-focus sealed tube	1789 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.021
Detector resolution: 1024x1024 with blocks 2x2 pixels mm^-1	θmax = 25.7°, θmin = 1.5°
ω scans	h = −32→32
Absorption correction: analytical face-indexed (SHELXTL; Sheldrick, 1990)	k = −31→31
Tmin = 0.962, Tmax = 0.972	l = −4→4
5001 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.034	H-atom parameters constrained
wR(F^2) = 0.092	w = 1/[σ^2(Fo^2) + (0.0395P)^2 + 0.3044P] where P = (Fo^2 + 2Fc^2)/3
S = 1.00	(Δ/σ)max = 0.001
2555 reflections	Δρmax = 0.16 e Å^−3
211 parameters	Δρmin = −0.13 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0073 (6)

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
C1	0.43052 (6)	0.43747 (6)	−0.0560 (5)	0.0530 (4)
C2	0.39567 (5)	0.47711 (6)	−0.1928 (4)	0.0507 (4)
C3	0.39960 (7)	0.53019 (6)	−0.2037 (5)	0.0637 (5)
H3	0.4281	0.5471	−0.1221	0.076*
C4	0.35911 (7)	0.55739 (7)	−0.3421 (5)	0.0716 (5)
H4	0.3606	0.5932	−0.3551	0.086*
C5	0.31700 (7)	0.53216 (7)	−0.4599 (5)	0.0709 (5)
H5	0.2905	0.5514	−0.5498	0.085*
C6	0.31305 (6)	0.47915 (7)	−0.4485 (4)	0.0620 (4)
H6	0.2845	0.4623	−0.5294	0.074*
C7	0.35313 (5)	0.45198 (6)	−0.3120 (4)	0.0505 (4)
C8	0.36066 (6)	0.39562 (6)	−0.2544 (4)	0.0549 (4)
N1	0.40708 (5)	0.39059 (5)	−0.1050 (4)	0.0576 (4)
H1	0.4202	0.3614	−0.0481	0.069*
O1	0.47194 (4)	0.44196 (5)	0.0825 (4)	0.0771 (4)
O8	0.33250 (5)	0.36014 (5)	−0.3216 (4)	0.0754 (4)
N11	0.51352 (6)	0.2500	0.4111 (5)	0.0480 (4)
C12	0.49062 (5)	0.29380 (6)	0.3116 (4)	0.0469 (3)
N13	0.44696 (4)	0.29605 (4)	0.1344 (3)	0.0477 (3)
C14	0.42707 (7)	0.2500	0.0534 (5)	0.0451 (5)
N15	0.51282 (5)	0.33841 (5)	0.3937 (4)	0.0591 (4)
H151	0.5408	0.3384	0.5064	0.071*
H152	0.4992	0.3672	0.3338	0.071*
N16	0.38334 (6)	0.2500	−0.1209 (5)	0.0545 (5)
H161	0.3693	0.2788	−0.1761	0.065*
N21	0.60560 (6)	0.2500	0.7669 (5)	0.0527 (5)
H21	0.5762	0.2500	0.6749	0.063*
C22	0.63169 (6)	0.29402 (6)	0.8484 (4)	0.0515 (4)
C23	0.68010 (5)	0.27671 (6)	0.9981 (4)	0.0476 (3)
C24	0.72093 (6)	0.30425 (6)	1.1162 (5)	0.0596 (4)
H24	0.7210	0.3402	1.1152	0.071*
C25	0.76186 (6)	0.27663 (7)	1.2364 (5)	0.0637 (5)
H25	0.7899	0.2943	1.3187	0.076*
O22	0.61646 (5)	0.33767 (4)	0.7962 (4)	0.0736 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0433 (8)	0.0552 (9)	0.0606 (9)	−0.0045 (7)	−0.0040 (7)	0.0014 (8)
C2	0.0479 (8)	0.0561 (9)	0.0480 (9)	−0.0035 (7)	0.0004 (7)	0.0029 (7)
C3	0.0661 (11)	0.0570 (10)	0.0681 (12)	−0.0078 (8)	0.0038 (9)	0.0030 (8)
C4	0.0862 (14)	0.0553 (9)	0.0734 (12)	0.0089 (9)	0.0081 (11)	0.0128 (9)
C5	0.0741 (12)	0.0772 (12)	0.0613 (11)	0.0201 (10)	0.0000 (10)	0.0139 (9)
C6	0.0528 (9)	0.0822 (12)	0.0510 (9)	0.0053 (9)	−0.0036 (8)	0.0050 (9)
C7	0.0462 (8)	0.0607 (9)	0.0445 (8)	−0.0031 (7)	0.0009 (7)	0.0037 (7)
C8	0.0520 (9)	0.0602 (9)	0.0525 (9)	−0.0109 (7)	−0.0036 (8)	0.0008 (8)
N1	0.0533 (8)	0.0493 (7)	0.0701 (9)	−0.0042 (6)	−0.0122 (7)	0.0052 (7)
O1	0.0565 (7)	0.0729 (8)	0.1020 (10)	−0.0042 (6)	−0.0204 (7)	0.0006 (7)
O8	0.0715 (8)	0.0689 (7)	0.0857 (9)	−0.0244 (6)	−0.0169 (7)	0.0016 (7)
N11	0.0431 (9)	0.0493 (9)	0.0515 (10)	0.000	−0.0024 (8)	0.000
C12	0.0432 (8)	0.0527 (8)	0.0449 (8)	−0.0026 (7)	0.0029 (6)	0.0024 (7)
N13	0.0422 (6)	0.0500 (7)	0.0510 (7)	−0.0014 (5)	0.0001 (6)	0.0034 (6)
C14	0.0395 (11)	0.0521 (11)	0.0437 (11)	0.000	0.0060 (9)	0.000
N15	0.0529 (8)	0.0502 (7)	0.0742 (10)	−0.0065 (6)	−0.0124 (7)	0.0054 (7)
N16	0.0432 (9)	0.0548 (10)	0.0656 (12)	0.000	−0.0060 (9)	0.000
N21	0.0434 (9)	0.0554 (10)	0.0593 (11)	0.000	−0.0062 (9)	0.000
C22	0.0520 (8)	0.0516 (8)	0.0510 (9)	−0.0009 (7)	−0.0005 (7)	0.0027 (7)
C23	0.0454 (8)	0.0556 (8)	0.0418 (8)	−0.0010 (7)	0.0024 (6)	0.0017 (6)
C24	0.0547 (9)	0.0607 (9)	0.0634 (10)	−0.0089 (8)	−0.0048 (8)	0.0011 (8)
C25	0.0465 (8)	0.0884 (11)	0.0562 (10)	−0.0086 (8)	−0.0045 (8)	0.0003 (9)
O22	0.0714 (8)	0.0531 (6)	0.0964 (10)	0.0033 (6)	−0.0185 (7)	0.0087 (7)

Geometric parameters (Å, º)

C1—O1	1.229 (2)	C12—N15	1.334 (2)
C1—N1	1.378 (2)	C12—N13	1.346 (2)
C1—C2	1.479 (2)	N13—C14	1.341 (2)
C2—C3	1.379 (2)	C14—N13^i	1.341 (2)
C2—C7	1.385 (2)	C14—N16	1.341 (3)
C3—C4	1.393 (2)	N15—H151	0.8600
C3—H3	0.9300	N15—H152	0.8600
C4—C5	1.375 (3)	N16—H161	0.8600
C4—H4	0.9300	N21—C22	1.371 (2)
C5—C6	1.377 (3)	N21—C22^i	1.371 (2)
C5—H5	0.9300	N21—H21	0.8600
C6—C7	1.381 (2)	C22—O22	1.217 (2)
C6—H6	0.9300	C22—C23	1.481 (2)
C7—C8	1.489 (2)	C23—C24	1.377 (2)
C8—O8	1.214 (2)	C23—C23^i	1.383 (3)
C8—N1	1.369 (2)	C24—C25	1.383 (2)
N1—H1	0.8600	C24—H24	0.9300
N11—C12^i	1.342 (2)	C25—C25^i	1.379 (3)
N11—C12	1.342 (2)	C25—H25	0.9300
O1—C1—N1	123.32 (14)	C12^i—N11—C12	115.32 (18)
O1—C1—C2	130.53 (15)	N15—C12—N11	117.61 (13)
N1—C1—C2	106.14 (13)	N15—C12—N13	117.58 (13)
C3—C2—C7	121.40 (15)	N11—C12—N13	124.80 (14)
C3—C2—C1	130.84 (15)	C14—N13—C12	114.74 (13)
C7—C2—C1	107.73 (14)	N13—C14—N13^i	125.55 (19)
C2—C3—C4	117.12 (17)	N13—C14—N16	117.22 (9)
C2—C3—H3	121.4	N13^i—C14—N16	117.22 (9)
C4—C3—H3	121.4	C12—N15—H151	120.0
C5—C4—C3	121.13 (17)	C12—N15—H152	120.0
C5—C4—H4	119.4	H151—N15—H152	120.0
C3—C4—H4	119.4	C14—N16—H161	120.0
C4—C5—C6	121.74 (17)	C22—N21—C22^i	112.47 (18)
C4—C5—H5	119.1	C22—N21—H21	123.8
C6—C5—H5	119.1	C22^i—N21—H21	123.8
C7—C6—C5	117.38 (17)	O22—C22—N21	124.44 (15)
C7—C6—H6	121.3	O22—C22—C23	129.39 (14)
C5—C6—H6	121.3	N21—C22—C23	106.16 (13)
C6—C7—C2	121.23 (16)	C24—C23—C23^i	121.17 (9)
C6—C7—C8	131.18 (15)	C24—C23—C22	131.20 (14)
C2—C7—C8	107.57 (13)	C23^i—C23—C22	107.61 (8)
O8—C8—N1	125.15 (16)	C23—C24—C25	117.70 (16)
O8—C8—C7	128.84 (15)	C23—C24—H24	121.2
N1—C8—C7	106.01 (13)	C25—C24—H24	121.2
C8—N1—C1	112.54 (13)	C25^i—C25—C24	121.13 (10)
C8—N1—H1	123.7	C25^i—C25—H25	119.4
C1—N1—H1	123.7	C24—C25—H25	119.4

Symmetry code: (i) x, −y+1/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···N13	0.86	1.96	2.818 (2)	174
N15—H151···O22	0.86	2.30	3.159 (2)	179
N15—H152···O1	0.86	2.27	3.124 (2)	169
N16—H161···O8	0.86	2.39	3.248 (2)	178
N21—H21···N11	0.86	1.95	2.803 (2)	173
C4—H4···O22^ii	0.93	2.51	3.278 (2)	139

Symmetry code: (ii) −x+1, −y+1, −z.