Step-stool conformation of a cyclic Schiff base derived from ethyl­enedi­amine and heptane-2,4,6-trione: evidence for partial hydrolysis in metal coordination

A Schiff base derived from ethyl­enedi­amine and heptane-2,4,6-trione, namely, 5,9,14,18-tetra­methyl-1,4,10,13-tetra­aza­cyclo­octa­deca-5,8,14,17-tetra­ene-7,16-dione (C₁₈H₂₈N₄O₂), abbreviated H₄daaden, was prepared and characterized for the first time by single-crystal X-ray diffraction. The atoms of the Schiff base occupy two different planes and thus the mol­ecule is essentially nonplanar. An axis running through the C—C atoms of the ethyl­enedi­amine groups separate the two planes and these two planes are connected by bridging ethyl­ene groups showing an angle of 117.34 (8)°. As a result, the side view of the mol­ecule shows a `step-stool' conformation. The nonplanar nature of the Schiff base plays an important role in metal coordination, which leads to partial hydrolysis of the ring structure.

Computing details

Data collection: APEX2 (Bruker, 2015); cell refinement: APEX2 (Bruker, 2015); data reduction: APEX2 (Bruker, 2015); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b).

5,9,14,18-Tetramethyl-1,4,10,13-tetraazacyclooctadeca-5,8,14,17-tetraene-7,16-dione

Crystal data

C18H28N4O2	Dx = 1.276 Mg m^−3
Mr = 332.44	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 1245 reflections
a = 6.9163 (4) Å	θ = 2.0–28.5°
b = 12.5609 (8) Å	µ = 0.09 mm^−1
c = 19.9264 (12) Å	T = 100 K
V = 1731.11 (18) Å^3	Prism frag, colorless
Z = 4	0.24 × 0.19 × 0.13 mm
F(000) = 720

Data collection

Bruker APEXII diffractometer	1833 reflections with I > 2σ(I)
profile data from θ/2θ scans	Rint = 0.027
Absorption correction: multi-scan (SADABS; Bruker, 2015)	θmax = 28.5°, θmin = 2.0°
Tmin = 0.980, Tmax = 0.989	h = −9→9processed/
19156 measured reflections	k = −16→16
2101 independent reflections	l = −26→26

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F^2 > 2σ(F^2)] = 0.035	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.094	w = 1/[σ^2(Fo^2) + (0.0463P)^2 + 0.4795P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max < 0.001
2101 reflections	Δρmax = 0.27 e Å^−3
118 parameters	Δρmin = −0.21 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. The single crystal X-ray diffraction data were recorded on a Bruker Smart 1000 diffractometer equipped with a CCD detector, using molybdenum K_α radiation (λ = 0.71073 Å). All data were collected at 100 K. The structures were solved and refined using the APEX4 v2021 4-0 software package.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.05303 (10)	−0.04672 (6)	0.42962 (3)	0.02367 (18)
N2	0.28758 (12)	0.14375 (7)	0.56538 (4)	0.0221 (2)
N1	0.34399 (13)	0.08857 (7)	0.42794 (4)	0.0235 (2)
H1	0.265 (2)	0.0384 (11)	0.4484 (7)	0.034 (2)*
C1	0.39987 (14)	0.19559 (8)	0.32716 (5)	0.0234 (2)
H1A	0.403490	0.262820	0.352087	0.035*
H1B	0.339886	0.207382	0.283228	0.035*
H1C	0.531908	0.169042	0.320961	0.035*
C2	0.28368 (14)	0.11502 (7)	0.36587 (5)	0.0193 (2)
C3	0.12097 (14)	0.06916 (7)	0.33860 (5)	0.0194 (2)
H3	0.084963	0.089348	0.294385	0.023*
C4	0.00123 (14)	−0.00794 (7)	0.37310 (5)	0.0189 (2)
C5	−0.17790 (13)	−0.03998 (7)	0.34211 (5)	0.0196 (2)
H5	−0.203869	−0.015000	0.298023	0.024*
C6	−0.31405 (13)	−0.10443 (7)	0.37216 (5)	0.0192 (2)
C7	0.42669 (14)	0.20225 (8)	0.52470 (5)	0.0222 (2)
H7A	0.537048	0.224022	0.553212	0.027*
H7B	0.364746	0.267604	0.507130	0.027*
C8	0.50186 (14)	0.13546 (8)	0.46575 (5)	0.0213 (2)
H8A	0.579942	0.181151	0.435670	0.026*
H8B	0.586648	0.078196	0.483041	0.026*
C9	−0.49507 (14)	−0.13417 (8)	0.33512 (5)	0.0237 (2)
H9A	−0.502898	−0.211818	0.331168	0.036*
H9B	−0.492636	−0.102365	0.290217	0.036*
H9C	−0.607884	−0.107746	0.359776	0.036*
H2	0.176 (2)	0.1212 (10)	0.5469 (7)	0.034 (2)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0246 (4)	0.0276 (4)	0.0188 (3)	−0.0052 (3)	−0.0036 (3)	0.0049 (3)
N2	0.0203 (4)	0.0263 (4)	0.0198 (4)	−0.0056 (3)	−0.0011 (3)	0.0019 (3)
N1	0.0251 (4)	0.0268 (4)	0.0187 (4)	−0.0082 (4)	−0.0021 (3)	0.0024 (3)
C1	0.0236 (5)	0.0237 (5)	0.0229 (5)	−0.0015 (4)	0.0032 (4)	0.0029 (4)
C2	0.0218 (5)	0.0176 (4)	0.0186 (4)	0.0025 (4)	0.0033 (3)	−0.0007 (3)
C3	0.0216 (5)	0.0204 (4)	0.0162 (4)	0.0019 (4)	0.0010 (3)	0.0015 (3)
C4	0.0208 (5)	0.0186 (4)	0.0173 (4)	0.0018 (4)	0.0014 (3)	−0.0013 (3)
C5	0.0217 (5)	0.0203 (4)	0.0168 (4)	0.0021 (4)	−0.0013 (3)	−0.0002 (3)
C6	0.0199 (4)	0.0178 (4)	0.0199 (4)	0.0032 (3)	−0.0004 (3)	−0.0031 (3)
C7	0.0215 (5)	0.0226 (5)	0.0225 (5)	−0.0041 (4)	0.0011 (4)	0.0002 (4)
C8	0.0193 (5)	0.0232 (5)	0.0214 (5)	−0.0029 (4)	−0.0012 (4)	0.0004 (4)
C9	0.0213 (5)	0.0241 (5)	0.0258 (5)	−0.0007 (4)	−0.0035 (4)	−0.0017 (4)

Geometric parameters (Å, º)

O1—C4	1.2783 (11)	C3—H3	0.9500
N2—C6^i	1.3514 (12)	C4—C5	1.4415 (13)
N2—C7	1.4569 (12)	C5—C6	1.3787 (13)
N2—H2	0.898 (14)	C5—H5	0.9500
N1—C2	1.3470 (12)	C6—C9	1.5006 (13)
N1—C8	1.4514 (12)	C7—C8	1.5343 (13)
N1—H1	0.928 (14)	C7—H7A	0.9900
C1—C2	1.5049 (13)	C7—H7B	0.9900
C1—H1A	0.9800	C8—H8A	0.9900
C1—H1B	0.9800	C8—H8B	0.9900
C1—H1C	0.9800	C9—H9A	0.9800
C2—C3	1.3760 (13)	C9—H9B	0.9800
C3—C4	1.4480 (13)	C9—H9C	0.9800
C6^i—N2—C7	127.39 (8)	C4—C5—H5	117.8
C6^i—N2—H2	112.3 (8)	N2^i—C6—C5	121.47 (9)
C7—N2—H2	119.7 (8)	N2^i—C6—C9	118.36 (9)
C2—N1—C8	127.55 (9)	C5—C6—C9	120.15 (9)
C2—N1—H1	112.8 (8)	N2—C7—C8	111.96 (8)
C8—N1—H1	119.4 (8)	N2—C7—H7A	109.2
C2—C1—H1A	109.5	C8—C7—H7A	109.2
C2—C1—H1B	109.5	N2—C7—H7B	109.2
H1A—C1—H1B	109.5	C8—C7—H7B	109.2
C2—C1—H1C	109.5	H7A—C7—H7B	107.9
H1A—C1—H1C	109.5	N1—C8—C7	111.37 (8)
H1B—C1—H1C	109.5	N1—C8—H8A	109.4
N1—C2—C3	120.84 (9)	C7—C8—H8A	109.4
N1—C2—C1	118.11 (9)	N1—C8—H8B	109.4
C3—C2—C1	121.06 (8)	C7—C8—H8B	109.4
C2—C3—C4	124.08 (9)	H8A—C8—H8B	108.0
C2—C3—H3	118.0	C6—C9—H9A	109.5
C4—C3—H3	118.0	C6—C9—H9B	109.5
O1—C4—C5	120.79 (9)	H9A—C9—H9B	109.5
O1—C4—C3	120.86 (9)	C6—C9—H9C	109.5
C5—C4—C3	118.35 (8)	H9A—C9—H9C	109.5
C6—C5—C4	124.39 (9)	H9B—C9—H9C	109.5
C6—C5—H5	117.8
C8—N1—C2—C3	−174.55 (9)	C3—C4—C5—C6	−173.43 (9)
C8—N1—C2—C1	5.77 (15)	C4—C5—C6—N2^i	−0.38 (15)
N1—C2—C3—C4	0.99 (15)	C4—C5—C6—C9	−179.26 (8)
C1—C2—C3—C4	−179.34 (8)	C6^i—N2—C7—C8	108.38 (11)
C2—C3—C4—O1	−7.49 (14)	C2—N1—C8—C7	109.08 (11)
C2—C3—C4—C5	172.54 (8)	N2—C7—C8—N1	50.53 (11)
O1—C4—C5—C6	6.60 (14)

Symmetry code: (i) −x, −y, −z+1.