title: Thermally induced interconversions of metal-pyrimidine-4,6-dicarboxylate polymers: a structural, spectroscopic, and magnetic study.
abstract: Continuing our work on the structural and magnetic aspects of the one-dimensional (1-D) coordination polymers of the [M(pmdc)(H(2)O)(2)] x H(2)O kind (M = Fe, Co, Ni, Cu, Zn; pmdc = pyrimidine-4,6-dicarboxylate), we have combined ab initio X-ray powder diffraction methods with in situ thermodiffractometry and thermal analyses to characterize the selective and reversible transformation of the [M(pmdc)(H(2)O)(2)] x H(2)O compounds (M = Fe, Co, Ni, Cu) into the bis-hydrated [M(pmdc)(H(2)O)(2)] counterparts by moderate heating, which is followed by an irreversible transformation into two-dimensional (2-D) anhydrous species. The structural features of the transient bis-hydrated species and of the completely dehydrated one are described for M = Cu. Remarkably, the first dehydration process does not alter the 1-D nature of the [M(pmdc)(H(2)O)(2)] chains; on the contrary, the second dehydration gives rise to the loss of the axially coordinated water molecules with a concomitant condensation of the 1-D chains into 2-D layers through ancillary carboxylate bridging groups. The magnetic properties of the anhydrous [M(pmdc)] species (M = Co, Ni, Cu) have been investigated, showing that these phases behave as 1-D antiferromagnets with interchain interactions. Notably, in the case of the [Ni(pmdc)] system, a weak ferromagnetic ordering, arising from a spin canting phenomenon with a blocking temperature of 13 K, is observed.
authors.affiliation: Dipartimento di Scienze Chimiche e Ambientali, Università dell'Insubria, via Valleggio 11, 22100 Como, Italy.
authors.forename: Norberto
authors.initials: N
authors.lastname: Masciocchi
authors.forename: Simona
authors.initials: S
authors.lastname: Galli
authors.forename: Giulia
authors.initials: G
authors.lastname: Tagliabue
authors.forename: Angelo
authors.initials: A
authors.lastname: Sironi
authors.forename: Oscar
authors.initials: O
authors.lastname: Castillo
authors.forename: Antonio
authors.initials: A
authors.lastname: Luque
authors.forename: Garikoitz
authors.initials: G
authors.lastname: Beobide
authors.forename: Wenguo
authors.initials: W
authors.lastname: Wang
authors.forename: M Angustias
authors.initials: MA
authors.lastname: Romero
authors.forename: Elisa
authors.initials: E
authors.lastname: Barea
authors.forename: Jorge A R
authors.initials: JA
authors.lastname: Navarro
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D008280:Magnetics; D019216:Metals, Heavy / Q000737:chemistry*; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D033362:Powder Diffraction; D011743:Pyrimidines / Q000737:chemistry*; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D002264:Carboxylic Acids; D019216:Metals, Heavy; D009942:Organometallic Compounds; D011743:Pyrimidines; C540719:pyrimidine-4,6-dicarboxylate