5,10,10,15,20,20-Hexamethylcalix[4]pyrrole 5,15-diethyl diester

In the title compound, C32H40N4O4, the pyrrole rings and ester groups adopt a 1,3-alternate conformation in which the alternating pyrrole and ester units are in opposite directions. The structure displays N—H⋯O hydrogen bonding and exhibits disorder [site occupancies of 0.81(2) and 0.71(2)] in the peripheral ethyl groups.

In the title compound, C 32 H 40 N 4 O 4 , the pyrrole rings and ester groups adopt a 1,3-alternate conformation in which the alternating pyrrole and ester units are in opposite directions. The structure displays N-HÁ Á ÁO hydrogen bonding and exhibits disorder [site occupancies of 0.81(2) and 0.71(2)] in the peripheral ethyl groups.
In this context, calix[4]pyrroles have emerged as molecules of particular interest because of their simple preparations in one-step and easy modification of their core structures.
The title compound is shown in Fig. 1. It exhibits a strong intermolecular H-bonding interaction as depicted in Fig. 2.
As it can be seen in Fig. 3, pyrrole units of title compound adopt 1,3-alternate conformation which is the nitrogen atoms of neighboring pyrroles oriented in opposite directions. It is also observed that the ester groups are in opposite directions according to calixpyrrole plane and meso-carbon atoms containing ester groups are connected to different pyrrole rings.

S2. Experimental
Synthesis of the title compound was carried out according to a previously reported procedure (Akar & Aydogan, 2005).
The sample grew as very large, yellow prisms by slow evaporation from methylene chloride/diethylether. The data crystal was cut from a large specimen.

S3. Refinement
The hydrogen atoms on carbon were calculated in ideal positions with isotropic displacement parameters set to 1.2 x Ueq of the attached atom (1.5 x Ueq for methyl hydrogen atoms). The hydrogen atoms on the pyrrole nitrogen atoms were observed in a difference Fourier map and refined with isotropic displacement parameters. Both methyl groups on the ester moieties were disordered about two orientations. The disorder was modeled in the same way for both groups. The site occupancy for one carbon atom orientation was assigned a variable x. The site occupancy factor for the other conformer was assigned the variable (1 -x). The variable x was refined while refining the two atoms with a single isotropic displacement parameter. At the same time, the geometry of the methyl carbon atoms were restrained to be equivalent. In this way, the site occupancy factor for C36 refined to 81 (2)% and that for C28 refined to 77 (2)%. The lower occupancy carbon atoms, C28A and C36A, were refined isotropically.      H atoms treated by a mixture of independent and constrained refinement where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.035 Δρ max = 0.26 e Å −3 Δρ min = −0.30 e Å −3 Extinction correction: SHELXTL/PC (Sheldrick, 1998), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0023 (5) 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 F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger. Both methyl groups on the ester moieties were disordered about two orientations. The disorder was modeled in the same way for both groups. The site occupancy for one carbon atom orientation was assigned a variable x. The site occupancy factor for the other conformer was assigned the variable (1 -x). The variable x was refined while refining the two atoms with a single isotropic displacement parameter. At the same time, the geometry of the methyl carbon atoms were restrained to be equivalent. In this way, the site occupancy factor for C36 refined to 81 (2)% and that for C28 refined to 77 (2)%. The lower occupancy carbon atoms, C28A and C36A, were refined isotropically.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ.