Homochiral transition-metal camphorate coordination architectures containing "piperazine-pyridine" ligands

[[abstract]]A total of five homochiral metal-organic coordination polymers (MOCPs) showing high thermal stability have been assembled from the reaction of divalent transition-metal ions (Co(2+), Zn(2+), and Cd(2+)), rigid enantiopure D-camphoric acid (D-H(2)Cam), and achiral neutral N,N'-bis(pyrid-4-yl) piperazine (bpypip) ligand under hydro(solvo)thermal conditions. Compound [Co(2)(D-Cam)(2)(bpypip)] (1) features a chiral-layered cobalt-camphorate coordination (4,4)-net, which is pillared by auxiliary linear N-tethering bpypip linkers to yield a homochiral three-dimensional coordination framework with Schlafli symbol of 4(4).6(10).8. Compounds [M(D-HCam)(2)(bpypip)] (2, M = Cd; 3, M = Zn) have nearly identical one-dimensional M-bpypip zigzag coordination-chain structures, in which each metal ion further attaches to two partially deprotonated monoanionic D-HCam terminals, which exhibit two types of partially deprotonating manner in 2 but only one type in 3. Through chain-to-chain C(= O)OH center dot center dot center dot O(carboxylate) hydrogen bonds, the zigzag coordination-chain becomes extended to a three-dimensional uninodal 6-connected supramolecular network, which can be considered as a result of a M-D-HCam-based 4-connected supramolecular 6(5).8-net intersected by M-bpypip-based zigzag coordination-chains. Of particular interest, the supramolecular assembly contains a couple of single-stranded right- (SRH) and left-handed (SLH) supramolecular helices and a couple of double-stranded right-(DRH) and left-handed (DLH) supramolecular helices, and therefore exists as a meso-net in topology, i.e., there is no spatial chirality. Compounds [M(2)(OH)(OAc)(D-Cam)(bpypip)] (4, M = Co; 5, M = Zn) have identically homochiral ladder-like chain structures having meso-M2 units and presenting three kinds of different anions, i.e., hydroxyl, acetate, and D-Cam. The obtained acetate anion may be generated from the hydrolyzation of dimethylacetamide (DMAc) under hydro(solvo) thermal conditions.[[note]]SC