In the series described in this work, the hydrothermal synthesis led to oxidation of the 5-methyl-pyrazinecarboxylate anion to the 2,5-pyrazinedicarboxylate dianion (2,5-pzdc) allowing the preparation of three-dimensional (3D) lanthanide(III) organic frameworks of formula {[Ln(2,5-pzdc)(HO)]·6HO} [Ln = Ce (1), Pr (2), Nd (3), and Eu (4)] and {[Er(2,5-pzdc)(HO)]·5HO} (5). Single-crystal X-ray diffraction on 1-5 reveals that they crystallize in the triclinic system, P1̅ space group with the series 1-4 being isostructural. The crystal structure of the five compounds are 3D with the lanthanide(III) ions linked through 2,5-pzdc dianions acting as two- and fourfold connectors, building a binodal 4,4-connected (4·68)(468)-mog network. The photophysical properties of the Nd(III) (3) and Eu(III) (4) complexes exhibit sensitized photoluminescence in the near-infrared and visible regions, respectively. The photoluminescence intensity and lifetime of 4 were very sensitive due to the luminescence quenching of the D level by O-H oscillators of four water molecules in the first coordination sphere leading to a quantum efficiency of 11%. Variable-temperature magnetic susceptibility measurements for 1-5 reveal behaviors as expected for the ground terms of the magnetically isolated rare-earth ions [F, H, I, F, and I for Ce(III), Pr(III), Nd(III), Eu(III), and Er(III), respectively] with M = 0 (2 and 4) and ±1/2 (1, 3, and 5). Q-band electron paramagnetic resonance measurements at low temperature corroborate these facts. Frequency-dependent alternating-current magnetic susceptibility signals under external direct-current fields in the range of 100-2500 G were observed for the Kramers ions of 1, 3, and 5, indicating slow magnetic relaxation (single-ion magnet) behavior. In these compounds, τ decreases with decreasing temperature at any magnetic field, but no Arrhenius law can simulate such a dependence in all the temperature range. This dependence can be reproduced by the contributions of direct and Raman processes, the Raman exponent (n) reaching the expected value (n = 9) for a Kramers system.
We have developed a new strategy for the design and synthesis of multifunctional molecular materials showing reversible magnetic and optical switching.
We herein present the synthesis and X-ray structures of five copper(II) complexes of formulae [Cu(bpca)(CF3SO3)(H2O)]·H2O (1), [Cu(bpca)(Phpr)(H2O)]·3/2H2O (2), {[Cu(bpca)]2[Cu(opba)(H2O)]}·H2O (3), {[Cu(bpca)]2(H2opba)}2·6H2O (4) and [Cu(bpca)(EtH2opba)]n (5), where bpca = bis(2-pyridylcarbonyl)amidate, Phpr = 3-phenylpropionate, CF3SO3(−) = triflate (anion of the trifluoromethanesulphonic acid), H4opba = N,N′-1,2-phenylenebis(oxamic acid), and EtH3opba = monoethyl ester derivative of the H4opba. 1 and 2 are mononuclear copper(II) complexes where the copper atom is five-coordinate in distorted square pyramidal surroundings with a tridentate bpca and a water molecule (1)/carboxylate oxygen (2) building the basal plane and a triflate oxygen (1)/water molecule (2) filling the apical position. 3 is a neutral tricopper(II) complex where the [Cu(opba)(H2O)]2− unit acts as a bis-bidentate ligand toward two peripheral [Cu(bpca)]+ fragments. The three crystallographically independent copper(II) ions in 3 are five-coordinate with two nitrogen and two oxygen atoms (inner copper atom)/three bpca-nitrogen and an oxamate oxygen (outer copper atom) building the basal plane plus a water molecule (inner copper)/an oxamate oxygen (outer copper) in the apical position (inner copper atom) of somewhat distorted square pyramidal surroundings. 4 is a centrosymmetric tetracopper(II) compound where four [Cu(bpca)]+ fragments are assembled by two H2opba2− groups adopting an unusual bidentate/bis-monodentate bridging mode. The two crystallographically independent copper(II) ions in 4 are also five-coordinate having the three bpca-nitrogens in basal positions, the other two sites of the distorted square pyramid being filled by two oxygens of either a bidentate oxamate (at one copper centre) or two bis-monodentate oxamates (at the other copper atom). 5 is a zigzag chain of [Cu(bpca)(H2O)]+ units which are connected through the EtH2opba− ligand adopting a bidentate/monodentate bridging mode across the monodeprotonated oxamate group. Each copper(II) ion in 5 is six-coordinate in an elongated octahedral CuN3O3 chromophore. The magnetic properties of 3–5 were investigated in the temperature range 1.9–300 K. 3 exhibits an intermediate intramolecular antiferromagnetic interaction [J = -65.8(2) cm(-1) with the Hamiltonian H = -J(S(Cu1)·S(Cu2) + S(Cu2)·S(Cu3))] which leads to a low-lying spin doublet at low temperatures. A weak antiferromagnetic coupling between the inner copper(II) ions occurs in 4 [J = -2.36(2) cm(-1), H = -JS1·S2)] and a very small intrachain antiferromagnetic interaction is observed in 5 [J = -0.17(1) cm(-1) with H = -J∑(i)S(i)·S(i+1)]. These values are analyzed by means of simple orbital symmetry considerations and compared with those previously reported for parent systems.
The knowledge of the one-synthon based supramolecular network of the propane-1,2,3-tricarboxylic acid (H 3 tca), commonly referred to as tricarballylic acid (1), induced us to look for new architectures of tricarballylate-containing lanthanide(III) cations having in mind that the structure of the complex [Ce(tca)(H 2 O) 2 ] n is the only reported example of this type of compounds. Three novel complexes of formulas [Gd(tca 4) have been synthesized, and their structures have been determined by X-ray diffraction on single crystals. 2 and 3 are isomorphous compounds. They exhibit a layered structure where the lanthanide atoms are nine-coordinated with three water molecules and six carboxylateoxygen atoms building a monocapped square antiprism surrounding and the tca ligands adopting a tris-bidentate coordination mode. 4 has a three-dimensional structure where two 10-coordinated, crystallographically independent lanthanum atoms [La(1) and La(2)] occur with three/two [La(1)/La(2)] water molecules and seven/eight [La(1)/La(2)] carboxylate-oxygens describing bicapped square antiprism surroundings. Two different tca groups are present in 4 both having in common the tris-bidentate coordination mode but acting in addition as monodentate and bis-monodentate ligands through one and two carboxylate groups, respectively. † In memoriam Prof. Xavier Solans. The authors have greatly benefited from numerous scientific discussions with Prof. Xavier Solans on X-ray diffraction, and they much enjoyed his enthusiasm, creativity, saVoir faire, and pedagogic virtues. Unfortunately, he passed away recently, but he will remain in our memory forever.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.