Six Flexible and Rigid Co(II) Coordination Networks with Dicarboxylate and Nicotinamide-Like Ligands: Impact of Noncovalent Interactions in Retention of Dimethylformamide Solvent

Abstract

Six mixed-ligand Co­(II) coordination polymers, {[Co­(adi)­(iso-nia)2]·dmf} n (1), [Co­(adi)­(iso-nia)2] n (2), {[Co2(suc)­(ac)2(iso-nia)4]­[Co2(suc)­(sucH)2(iso-nia)4]­·2dmf} n (3), [Co­(adi)­(nia)2] n (4), {[Co­(bdc)­(nia)2]­·dmf} n (5), and {[Co­(mal)­(S-nia)­(H2O)]·dmf} n (6), were synthesized and characterized by single crystal X-ray analysis. They are based on four dicarboxylic acids, namely, malonic (H2mal), succinic (H2suc), adipic (H2adi), and 1,4-benzenedicarboxylic (H2bdc) acids, as well as three nicotinamide-like ligands, isonicotinamide (iso-nia), nicotinamide (nia) and thionicotinamide (S-nia). Compounds 1, 2, and 3 represent one-dimensional coordination polymers, whereas 4, 5, and 6 exhibit two-dimensional structures. The coordination arrays in 1–5 are built from the similar [Co2(COO)2] binuclear clusters, while framework 6 is based on mononuclear metal nodes. All crystal lattices are supported by hydrogen bonding with nicotinamide-like ligands acting as pillars or dangling terminal ligands. Four crystal lattices 1, 3, 5, and 6 host dmf solvent via NH···O hydrogen bonding and π–π stacking interactions with the coordination networks. Details of the reversible dmf release–uptake by 1 and 2, and contribution of hydrogen bonding in stabilization of the solvent-free structures 2 and 4 are discussed. All new solids were characterized by IR spectroscopy and thermogravimetric analysis, while magnetic measurements are reported for compounds 1, 5, and 6. The magnetic data show the typical behavior of Co­(II) ions originating from pronounced zero-field splitting within the ground state with contributing effects from weak antiferromagnetic exchange interactions.

Consequences of twisting of the flexible arms of imidazole-derived urea in zinc-dicarboxylate coordination polymers

“…In the thermogravimetry analysis, CP1 , having no guest molecules, did not show a weight loss until 200 °C; whereas CP2 , having two ethanol molecules per zinc ion, showed a weight loss around 100–200 °C due to the loss of two ethanol molecules and one water molecule. Amide-containing porous coordination polymers undergo single crystal to single crystal (SCSC) transformation upon desolvation; 34 however, CP2 did not undergo such a transformation.…”

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

“…Following the thermogravimetric analysis and previously reported SC−SC transitions by removal of solvent molecules from host frameworks, 49,51,60 the loss of lattice water and coordination water molecules can be achieved by heating 1 at different temperatures for different hours. Upon heating to 130 °C for 2 h, compound 1 experiences a SC−SC structural transformation to form neutral [Co(H 2 L)(H 2 O) 2 ]•0.5H 2 O (2) without apparent color change (Figure 6).…”

“…So far, SC−SC transformation induced by guest removal/inclusion without bond cleavage has been studied extensively. 49,50 In contrast, examples involving cleavage and formation of covalent or coordinative bonds, which results in a change of coordination number, 51 geometry, dimensionality, chirality, interpenetration, etc., are less common. 52−54 Experimentally, powder X-ray diffraction (PXRD), singlecrystal X-ray diffraction (SCXRD), and atomic force microscopy (AFM), as well as spectroscopic analytical tools such as nuclear magnetic resonance (NMR), and thermogravimerty (TG) have been applied to monitor solid-state structural transformations.…”

“…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. So far, SC–SC transformation induced by guest removal/inclusion without bond cleavage has been studied extensively. , In contrast, examples involving cleavage and formation of covalent or coordinative bonds, which results in a change of coordination number, geometry, dimensionality, chirality, interpenetration, etc., are less common. − …”

Exploring Reversible Thermochromic Behavior in a Rare Ni(II)-MOF System

“…The color produced by d–d electron transitions between energy levels of transition-metal ions in a coordination compound falls within the visible spectroscopy region. (ii) The absorption bands that resulted from d–d transitions are related strongly to the crystal field around the transition-metal ions in coordination complexes, which can be affected by external stimuli, such as pressure, irradiation, or temperature change. , However, the thermochromic behaviors of the majority of the reported MOFs are either irreversible , or reversible but need cumbersome and time-consuming regeneration processes. ,− In addition, in most cases, the measurable temperature range is limited, resulting from the limited color changes or the poor stability of the materials. − ,− Table S1 provides some information about the thermochromic materials discussed above. In the meantime, the poor cyclability of most thermochromic MOFs reported has been, so far, preventing the development and application of this kind of “smart” material (Table S1).…”