Chiral and Noncentrosymmetric Metal–Organic Frameworks Featuring a 2D → 3D Parallel/Parallel Inclined Subpolycatenation

Five chiral and noncentrosymmetric
metal–organic frameworks,
namely, {[Co­(TIPA)­(trans-chdc)­(H2O)]·H2O}n (1), {[Ni­(TIPA)­(trans-chdc)­(H2O)]·H2O}n (2), {[Co­(TIPA)­(seb)1/2]­(NO3)·H2O}n (3), {[Ni­(TIPA)­(seb)1/27]­(NO3)·H2O}n (4), and {[Zn2(TIPA)­(btc)­(μ2-OH)]·4H2O}n (5), have been synthesized
based on the N-center tripodal TIPA ligand, where TIPA is tris­[4-(1H-imidazol-1-yl)-phenyl]­amine, H3btc is 1,3,5-benzenetricarboxylic
acid, trans-H2chdc is trans-1,4-cyclohexanedicarboxylic acid, and H2seb is sebacic
acid. Complexes 1 and 2 are isostructural,
crystallize in the chiral orthorhombic space group P212121, and contain a 2D →
3D parallel/parallel inclined subpolycatenation based on (6,3) layers.
The two sets of layers of subpolycatenation are interconnected by
right-handed Co­(trans-chdc) helical chain, forming
a self-catenated framework. Complexes 3 and 4 are also isostructural and crystallize in the chiral monoclinic
space group C2. They also contain a 2D → 3D
parallel/parallel inclined subpolycatenation based on (6,3) layers.
Complex 5 crystallizes in the noncentrosymmetric space
group Pna21. Similarly to complexes 1–4, it also contains a 2D → 3D
parallel/parallel inclined subpolycatenation based on (6,3) dinuclear
Zn-TIPA layers. Meanwhile, the btc3– ligand with
a trimonodentate coordination mode connects the dinuclear Zn unit
to form a 2D (6,3) Zn-btc layer. The combination of the two types
of interconnected 2D nets results in a self-catenated framework. SHG
measurements on complexes 1–5 reveal
that complexes 1 and 2 display modest SHG
responses that are approximately 3 and 4 times that of KH2PO4 (KDP). The SHG responses of 3 and 4 are about the same as those of 1 and 2, respectively. Complex 5 has a strong SHG response,
and its SHG efficiency is approximately 10 times that of KDP. In addition,
the photoluminescent properties and thermal stabilities of these complexes
were studied in the solid state.