Temperature-dependent polymorphism and magnetic properties of three-dimensional copper pyromellitate coordination polymers containing 4,4′-dipyridylamine

• Copper pyromellitate (pyro) coordination polymers with 4,4′-dipyridylamine (dpa).
• Higher-temperature phase 1 has 3-D anionic trinodal network with H2dpa cations.
• Lower-temperature phase 2 has rare 3-D frl network.
• Dimers and chains in 1 show antiferromagnetism, trimers in 2 show ferromagnetism.

A pair of three-dimensional divalent copper pyromellitate (1,2,4,5-benzene-tetracarboxylate, pyro) coordination polymers containing 4,4′-dipyridylamine (dpa) was hydrothermally prepared and structurally characterized by single-crystal X-ray diffraction. The higher-temperature phase {[H2dpa][Cu3(pyro)2(H2O)3]·2.5H2O}n (1) displays an acentric 3-D 4,4,6-connected anionic network with (445.6)(5482)(44546374) topology, featuring {Cu2(OCO)4} paddlewheel dimers and isolated copper ions. Charge-balancing H2dpa cations are embedded in incipient voids. Prepared at lower temperature, {[Cu3(pyro)2(dpa)2(dpaH)2]·3H2O}n (2) manifests a 3-D 4,4,4-connected neutral network with uncommon (4264)4(6482) frl topology based on {Cu3(OCO)2} linear trimers. Antiferromagnetic coupling (J=–82(5) cm–1) was observed within the {Cu2(OCO)4} dimeric units in 1, while weak ferromagnetic coupling (J=1.0(4) cm–1) was evident for the {Cu3(OCO)2} linear trimers in 2. Thermal degradation behavior of these new materials is also presented.

Two copper pyromellitate coordination polymers containing 4,4′-dipyridylamine were prepared. The higher-temperature phase {[H2dpa][Cu3(pyro)2(H2O)3]∙2.5H2O}n displays an acentric 3-D trinodal anionic network with (445.6)(5482)(44546374) topology, featuring antiferromagnetically coupled {Cu2(OCO)4} paddlewheel dimers and isolated copper ions.Figure optionsDownload as PowerPoint slide