Homochiral zinc benzene-1,3,5-tricarboxylate coordination networks with a chiral nitrogen ligand or template: Spontaneous resolution of a twofold interpenetrated 2D sql (4,4) network and formation of enantiopure 3D sra (SrAl2) networks

Abstract

A pair of homochiral enantiomorphic two-fold interpenetrated, mixed-ligand coordination polymers (CPs), 2D-{[Zn(μ-Hbtc)(μ-R-btrip)]·H2O}n1 and 2D-{[Zn(μ-Hbtc)(μ-S-btrip)]·H2O}n2, were found in a racemic conglomerate in space group P212121 with enantiomorphous crystals by spontaneous resolution (H3btc=benzene-1,3,5-tricarboxylic acid, trimesic acid). The racemic ligand 1,2-bis(1,2,4-triazol-4-yl)propane (rac- or R,S-btrip) spontaneously resolves upon coordination to Zn(II) and crystallization from Zn(NO3)2·6H2O for 1 or ZnBr2 for 2, in presence of the trimesic acid (H3btc) under hydrothermal conditions. Single-crystal analysis of 1 and 2 revealed a chiral two-dimensional sql (4,4) network based on the interconnection of {Zn(Hbtc)} and {Zn(btrip)} chains at the Zn atom. Each 2D sql network is 2-fold interpenetrated by a symmetry related net. The interpenetration appears controlled by triazole–C–H⋯N hydrogen bonds. When the enantiopure Schiff base 2-((E)-(1-(4-methoxyphenyl)ethylamino)methyl)phenol (N-(1-(4-methoxyphenyl)ethyl)salicylaldimine) was reacted with ZnSO4 and H3btc in water/methanol the imine CN bond hydrolyzed retro-synthetically to the aldehyde and the amine which was protonated to the ammonium cation. The in-situ formed enantiopure (R) or (S)-1-(4-methoxyphenyl)ethylammonium cation was incorporated as a template in the crystallization of the anionic 3D-network {bis(benzene-1,3,5-tricarboxylato-κ4O:O′:O″:O‴′)dizinc(II)}, {[Zn2(μ4-btc)2]2−}n in the chiral compounds {[(R)- or (S)-4-CH3OC6H4CH(CH3)NH3]2[Zn2(μ4-btc)2]·2H2O}n (3 or 4, respectively). The 3D-network exhibited sra (SrAl2, zeolite ABW) topology. The ammonium cations are positioned by charge-assisted N–H(+)⋯(−)O (carboxylato) H-bonds and charge-assisted π-stacking in the anionic framework.