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 [Zn2(tib)4/3(L(1))2]·DMA (1) and [Zn2(tib)4/3(L(2))2]·H2O (2) (tib = 1,3,5-tris(1-imidazolyl)benzene, H2L(1) = biphenyl-4,4'-dicarboxylic acid, H2L(2) = 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 L(1) 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(5)·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.