No abstract

A novel series of copper(II) coordination polymers [Cu2(O2CC8H9)4(pyz)]n (1), [Cu2(O2CC8H9)4(dps)]n (2), {[Cu(O2CC8H9)2(dps)(H2O)]·H2O}n (3), {[NaCu(O2CC8H9)2(bpm)(NO3)]·H2O}n (4), and [Cu4(O2CC8H9)6(OH)2(bpp)2]n (5) [O2CC8H9− = 3-phenylpropionate anion, pyz = pyrazine, dps = di(4-pyridyl)sulfide, bpm = 2,2′-bipyrimidine, and bpp = 1,3-bis(4-pyridyl)propane] have been synthesized and magneto-structurally investigated. Compounds 1 and 2 belong to a large group of copper(II) carboxylates where bis-monodentate pyz (1) and dps (2) ligands connect the paddle-wheel [CuII2(μ-O2CC8H9)4] units leading to alternating copper(II) chains. The structure of 3 consists of uniform chains of trans-[CuII(O2CC8H9)2] units linked by the bis-monodentate dps ligand. Compound 4 consists of heterobimetallic chains where [NaI2CuII2(μ-O2CC8H9)4(NO3)2] units are doubly bridged by bis-bidentate bpm ligands. Compound 5 is also a chain compound whose structure is made up by tetranuclear [CuII4(μ3-OH)2(μ-O2CC8H9)4(O2CC8H9)2] units which are doubly bridged by bis-monodentate bpp ligands. The magnetic properties were investigated in the temperature range 1.8–300 K. Strong antiferromagnetic interactions across the quadruple syn–syn carboxylate are observed in 1 and 2 [J = −378 (1) and −348 cm−1 (2)] whereas a weak ferromagnetic coupling through the double out-of-plane oxo(carboxylate) bridge occurs in 4 [J = +2.66 cm−1], the spin Hamiltonian being defined as H = −JS1·S2 with S1 = S2 = SCu = 1/2. A quasi Curie law is observed for 3 (θ = −0.36 cm−1), the bis-monodentate dps ligand being a very poor mediator of magnetic interactions. The analysis of the magnetic properties of 5 is quite complex because of the presence of two crystallographically independent tetracopper(II) units with single-μ-hydroxo, di-μ-hydroxo, μ3-hydroxo and single-μ-hydroxo plus double syn,syn carboxylate bridges in each one. The nature and values of the magnetic couplings for 5 obtained by fitting (intermediate, strong and weak antiferromagnetic interactions for the three former exchange pathways respectively, and intermediate ferromagnetic interactions for the latter one) were substantiated by DFT type calculations.

Alternating anionic and cationic slices (1) and supramolecular layers (2) resulted from the assembly between [Cu(bpca)]+ and polypyridine ligands.

The preparation, general characterization, and experimental and theoretical photoluminescence investigations of a new europiumIII metal–organic framework [EuHbtec] n 1 supported by 1,2,4,5-benzenetetracarboxylic acid, H4btec (pyromellitic acid), are discussed in this work. The crystal structure was obtained from X-ray powder diffraction (XRPD), with the data collected at the MCX beamline of ELETTRA synchrotron. In this structure, the monoprotonated Hbtec3– ligands act in three different coordination modes to EuIII centers: μ2-η1:η2 chelating/bridging, η2 chelating, and η1 monodentate modes. The three-dimensional (3D) network is constructed by secondary building units (SBU) chains, connected through carboxylate groups of the Hbtec3– ligands. Using the Sparkle/RM1 model, the ground-state geometry of [EuHbtec] n 1 was calculated in the solid phase and then used to obtain the several investigative spectroscopic parameters. This study demonstrates that intense luminescence occurs through ligand sensitization. The exceptional thermal stability is proven by thermogravimetric analysis, with the network collapsing at 489 °C, the largest among the congener compounds. Thus, by combining its intense emission and high thermal stability, [EuHbtec] n 1 was utilized for marking of gunshot residues (GSRs), with its preliminary tests showing very promising results for applications in forensic contexts and public safety.

In this work we describe the preparation, spectroscopic, thermal and structural characterization, and cryomagnetic investigation of four new polymorphic derivatives of the [M2(H2mpba)3]2– mesocate of formulas {[K2(dmf)2(H2O)2]­[M2(H2mpba)3]·2H2O} n (M = Co (1), Ni (2)) and [M­(tppz)2]­[M2(H2mpba)3]·9H2O (M = Co (3), Ni (4)) (H4mpba = 1,3-phenylenebis­(oxamic) acid), tppz = 2,3,5,6-tetrakis­(2-pyridyl)­pyrazine). Pairs 1/2 and 3/4 are isomorphous compounds exhibiting a triple-stranded dinuclear motif, [M2(H2mpba)3]2–. 1 and 2 exhibit a three-dimensional network with [M2(H2mpba)3]2– mesocates interlinked by potassium­(I) ions. 3 and 4 present a brick and mortar network, where the “brick” is [M2(H2mpba)3]2– + [M­(tppz)2]2+ and the “mortar” refers to water molecules, where the electroneutrality of the motif is achieved by the [M­(tppz)2]2+ cationic complex. The dc magnetic data for 1–4 in the temperature range 1.9–300 K reveal the occurrence of magnetically isolated high-spin cobalt­(II) of the mesocate units in 1 and 3 plus a thermally induced spin crossover behavior of the [Co­(tppz)2]2+ unit in 3, whereas 2 and 4 exhibit Curie law behavior. Out-of-phase ac signals are observed for 1 and 3 at temperatures below 14 K under zero and nonzero applied dc fields, which are characteristic of the occurrence of slow magnetic relaxation in these systems, thus being new examples of single-molecule magnets (SMMs).