Two new zinc(II) coordination complexes with helix characteristics showing both interpenetration and self-catenation features: a platform for the synthesis of chiral and catenated structures assembled by length-modulated dicarboxylates.

Two new zinc coordination complexes, namely [Zn-2(tib)(4/3)(L-1)(2)].DMA (1) and [Zn-2(tib)(4/3)(L-2)(2)].H2O (2) (tib = 1,3,5-tris(1-imidazolyl)benzene, H2L1 = biphenyl-4,4'-dicarboxylic acid, H2L2 = 4,4'-(2,2'-oxybis(ethane-2,1-diyl)bis(oxy))dibenzoic acid and DMA = N,N-dimethylacetamide), are obtained using achiral mixed ligands and characterized using elemental analysis, IR and X-ray crystallography. Compounds 1 and 2 both display intriguing structural features of both interpenetration and self-catenation. By careful inspection of the two structures, we found that the Zn(II) cations, the tib ligands, and the dicarboxylic anions show the same coordination modes or analogous configurations. Compound 1 is chiral, which was confirmed by measuring the optical rotation of the bulk samples using solid-state circular dichroism (CD). It is comprised of two crystallographically independent interpenetrated 3D motifs, each containing interlaced triple-stranded right- and left-handed Zn-L-1-Zn helical chains and chiral 2D [Zn(tib)(2/3)] layers. Both motifs display binodal (3,4)-coordinated 3D self-catenated networks with the point symbol (10(3))(2)(10(6))(3) and the vertex symbols [10(13).10(13).10(13)] and [10(7).10(7).10(8).10(10).10(11).10(11)]. However, the two types of helical chains are not racemic due to the differences between the two kinds of L1 anions, and the two types of chiral 2D [Zn(tib)(2/3)](2+) layers are not enantiomeric either due to the different configurations of the tib ligands. Therefore, the two motifs are not enantiomers. Compound 2 is achiral, containing Zn-L-2-Zn zigzag chains that span into three directions and chiral 2D [Zn(tib)(2/3)] layers. The overall 3D network is a new binodal (3,4)-coordinated self-catenated network with the point symbol (10(3))(2)(10(6))(3) and the vertex symbols [10(7).10(7).10(7)] and [10(2).10(4).10(5).10(3).10(5).10(5)]. Two of these networks interpenetrate. Their chiral and achiral structures are mainly modulated by the length of the dicarboxylates. As expected, compounds 1 and 2 show photoluminescence behaviors and compound 1 shows a ferroelectric behavior. Thermogravimetric studies of 1 and 2 have also been performed. We examined all 48 known structures containing the tib ligand and drew the conclusion that the metal + tib combination, modulated by the prolonged L ligands, can be a good basis for new chiral and catenated structures.