Investigations on the phase behaviors and structural properties of mono-, di-and poly-valent metal carboxylates are reviewed with reference to developments in experimental and theoretical concepts surrounding their liquid crystalline properties. The main methods of structural investigation such as X-ray diffraction, infrared and 13 C-NMR spectroscopies are examined in detail on the basis of common synthetic routes leading to the isolation of pure compounds. A detailed review of the thermal behaviors of several metal carboxylates is presented along with proposed theories and molecular models for odd-even alternation, chain length effects, phase structures and mesophase formation. Theories explaining the effects of metal ion radii and chain unsaturation are also discussed. Proposed degradation mechanisms resulting in the formation of various products and kinetic studies are also considered. Though this review highlights a number of investigations on the structural and phase properties of the mostly widely studied carboxylates, the results presented here strongly indicate that there is room for further studies on some of these systems.

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Five isoreticular lanthanide (Ln) metal‐organic frameworks (MOFs) – Er(bdc)(HCOO) (1a), Dy(bdc)(HCOO) (1b), Tb(bpdc)(HCOO) (2a), Gd(bpdc)(HCOO) (2b) and Tb(bpydc)(HCOO) (3) (bdc = 1,4‐benzenedicarboxylate, bpdc = 4,4′‐biphenyldicarboxylate and bpydc = 2,2′‐bipyridine‐5,5′‐dicarboxylate) – were synthesized under solvothermal conditions. The complexes were characterized by powder X‐ray diffraction, elemental analyses, infrared spectroscopy and single‐crystal X‐ray crystallography. Each LnIII ion is eight‐coordinated and forms a binuclear pseudo‐paddlewheel secondary building unit (SBU), [Ln2(CO2)2(CO2)2]. The SBUs are interconnected into 2D Ln–carboxylate nets, which act as tertiary building units (TBUs) that are linked by the rigid organic linkers to form 3D pillared frameworks. Preliminary luminescence studies reveal that energy transfer from Tb3+ to Eu3+ trace impurities is active in crystals of 2a and 3 and contributes to interesting temperature‐dependent photoluminescence. At 298 K, under UV excitation, 2a is lilac and 3 glows bright red, whereas at 77 K both 2a and 3 emit green light. Together with the previously published Tb(bdc)(HCOO), Eu(bdc)(HCOO), Gd(bdc)(HCOO) and Ln(bpedc)(HCOO) (bpedc = biphenylethene‐4,4′‐dicarboxylate), these complexes form the first examples of isoreticular LnMOFs.

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