Synthesis and crystal structure of ammonium (picrate) (dibenzo-18-crown-6)

Abstract

NH4(Pic)(DB18C6) (Pic=picrate and DB18C6=dibenzo-18-crown-6), (C26H30N4O13) FW 606.56, arthorhombic,Pmn21,a=26.045(5),b=12.055(3),c=8.982(3) A,V=2820(1) A3,Z=4,D c =1.429 g/cm3, CuKα, λ=1.54184 A, μ(CuKα)=9.5 cm−1,F(000)=1272,T=298 K. The structure has been refined toR=0.0475 for 2617 unique observed reflections. In the lattice the 1:1 complex exists as a 2:2 dimer in which the crown are coupled through the Pic anions and NH4 + cations. The asymmetric unit consists of two independent half crown ethers of which two opposite O atoms are on the mirror plane, two half ammonium cations of which the N and two H atoms are also on the mirror plane while the Pic anion is in a general position. Relative to each other, the corwn ethers are shifted by about 7.3 A alongb and 1 A alongc. The 1:1 sandwich of NH4 with DB18C6 and Pic on dimerisation becomes a ‘club pseudo-sandwich’ with three phenyl rings on either side of the mirror plane, thus forming a nearly parallel stack with a 3.6 A inter-ring distance. The NH4 ions hold the structure; two H atoms on the mirror plane are hydrogen-bonded to the opposite oxygens of the crown located on the purely aliphatic part of the ring (2.10(1), 2.06(3) and 2.26(3), 2.05(1) A) for the two independent crowns, respectively, while the other two H atoms form mirror-related bifurcated hydrogen bonds with the phenoxide oxygen (1.99(1) and 2.01(1) A) and theo-nitrogen oxygen (2.44(2) and 2.34(1) A) of the picrates.