From (3,6)-Connected kgd, chiral anh to (3,8)-connected tfz-d Nets in Low Nuclear Metal Cluster-Based Networks with Triangular Pyridinedicarboxylate Ligand

Abstract

Four novel coordination polymers based on asymmetric triangular 5-(4′-carboxylphenyl) nicotinic acid (H2cpna), namely, Ni(cpna)(H2O)2 (1), M2(cpna)2(H2O)3·0.5H2O·DMF [M = Ni for (2), Co for (3)] and Ni3(Hcpna)2(cpna)2(H2O)4·2H2O (4), have been synthesized under solvothermal conditions. All of the four compounds contain low nuclear metal clusters as secondary building units (SBUs). Complex 1 exhibits two-dimensional (3,6)-connected (43)2(46.66.83)-kgd topology, in which cpna ligands and edge-shared dinuclear SBUs act as 3-connected and 6-connected nodes, respectively. Compounds 2 and 3 are constructed by corner-shared dinuclear SBUs and show an unprecedented (3,6)-connected chiral (42.6)2(44.62.88.10)-anh (flu-3, P6222) topology. In 4, linear trimers are ligated by six cpna ligands to form a planar (43)2(46.66.83)-kgd layer, and adjacent layers are further linked by Hcpna– ligands through Ni–O and Ni–N bonds to form three-dimensional (3,8)-connected (43)2(46.618.84)-tfz-d net. Both 1 and 4 crystallize in the triclinic crystal system with symmetric space group P̅1, which result in an equal ratio of (R)- and (S)-cpna isomers. Isostructural 2 and 3 crystallize in a trigonal crystal system with the chiral space group P3221, and a single crystal contains a sole optical isomer of cpna, although bulk crystals are a racemic mixture. Variable-temperature magnetic susceptibility measurements reveal ferromagnetic coupling of edge-shared dimers in 1, antiferromagnetic coupling of corner-shared dimers in 2 and 3, and ferrimagnetic coupling of linear trimers in 4.

Tunable Emission and Selective Luminescence Sensing in a Series of Lanthanide Metal–Organic Frameworks with Uncoordinated Lewis Basic Triazolyl Sites

“…Thus, 1-Tb possesses a binodal (3,8)-connected net with the point symbol of (4 3 ) 2 (4 6 ·6 18 ·8 4 ) calculated by TOPOS (Figure d) . Comparing with the reported (3,8)-connected nets, the topology of 1-Tb belongs to tfz-d type net. − …”

Six Co(II) Coordination Polymers Based on Two Isomeric Semirigid Ether-Linked Aromatic Tetracarboxylate Acid: Syntheses, Structural Comparison, and Magnetic Properties

“…For complex 1 , as shown in Figure , the χ M T value is 18.08 cm 3 K mol –1 at 300 K, almost twice higher than the expected value of 9.375 cm 3 K mol –1 for five Co­(II) ions independent ( g = 2.0, S = 3/2), or the value for the reported ones with the similar Co­(II) cluster. , This indicates the importance of orbital contribution generated from the high-spin octahedral Co­(II) ions. , As the sample was cooling down, the χ M T value decreased gradually and reached the value of 1.66 cm 3 K mol –1 at 2 K. While, the χ M value increased smoothly along with the decrease of temperature. These results clearly manifest that the presence of dominant antiferromagnetic coupling interactions between the Co­(II) ions and the structure of the carboxylate and hydroxyl groups in the [Co 5 (μ 3 -O) 2 N 4 (COO) 8 ] 2– pentanuclear cluster may be responsible for this phenomenon. − To further estimate the intramolecular exchange constant, the χ M –1 – T was plotted and it well obeys the Curie–Weiss law above 15 K, with C = 20.37 cm 3 K mol –1 and θ = −44.40 K; this also reveals the dominant antiferromagnetic interactions between the Co­(II) ions and the presence of spin–orbit coupling . To our disappointment, we could not find an exact magnetic solution to fit the magnetic value for such a complicated pentanuclear cluster.…”

“…44−46 To further estimate the intra-molecular exchange constant, the χ M −1 −T was plotted and it well obeys the Curie−Weiss law above 15 K, with C = 20.37 cm 3 K mol −1 and θ = −44.40 K; this also reveals the dominant antiferromagnetic interactions between the Co(II) ions and the presence of spin−orbit coupling. 47 To our disappointment, we could not find an exact magnetic solution to fit the magnetic value for such a complicated pentanuclear cluster.…”

Tunability in Metal Coordination Sphere, Ligand Coordination Mode, Network Topology, and Magnetism via Stepwise Dehydration Induced Single-Crystal to Single-Crystal Transformation

“…Metal–organic frameworks (MOFs) or coordination polymers (CPs) have received considerable attention in the past few decades owing to their potential applications in the fields of gas separation, − catalysis, sensing, , chirality, magnetism, optics, etc. − Since the first reported single-crystal to single-crystal (SC–SC) transformation for MOFs/CPs in 2002, − an arising interest in these crystalline materials is the stimuli-responsive SC–SC transformation between solid phases, which maintains the integrity before and after the transformation. This provides opportunities to understand solid-state transformations and to prepare new functional materials under exogenous stimuli such as thermal, − light, humidity, redox, solvent molecules, − mechanical forces, , and anions or cations. − These dynamic SC–SC transformations involving solid-state reactivity and structural transformation are rarely observed because the molecules are rigidly and steadily fixed within the crystal lattices. ,− That is to say, SC–SC transformations mostly occur through the minor movement of atoms as large changes of atoms or groups within lattice often destroy single crystals and yield polycrystalline powder.…”