Synthesis, Structure and Photoluminescence Properties of Cd and Cd-Ln Pentafluorobenzoates with 2,2′:6′,2′-Terpyridine Derivatives

Six new complexes [Cd(tpy)(pfb)2] (1, tpy = 2,2′:6′,2″-terpyridine), [Ln2Cd2(tpy)2(pfb)10] (Ln = Eu (2Eu), Tb (2Tb)), [Ln2Cd2(tbtpy)2(pfb)10]·2MeCN (Ln = Eu (3Eu), Tb (3Tb), tbtpy = 4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine), [Eu2Cd2(tppz)(pfb)10]n (4, tppz = 2,3,5,6-tetra-(pyridin-2-yl)pyrazine) based on pentafluorobenzoic acid (Hpfb) have been prepared and investigated. The effect of tridentate ligands on geometry heterometallic scaffolds synthesized complexes is discussed. The supramolecular crystal structures of the new compounds are stabilized by π-π, C-F···π, C-H···O, C-H...F, F….F interactions. Non-covalent interactions have been studied using Hirschfeld surface analysis. The obtained compounds were characterized by single-crystal and powder X-ray diffraction, luminescence spectroscopy, IR spectroscopy, CHN analysis. Complexes 2Ln and 3Ln exhibit metal-centered photoluminescence, but the presence of ligand luminescence bands indicates incomplete energy transfer from the d-block to the lanthanide ion.

Cadmium-Inspired Self-Polymerization of {LnIIICd2} Units: Structure, Magnetic and Photoluminescent Properties of Novel Trimethylacetate 1D-Polymers (Ln = Sm, Eu, Tb, Dy, Ho, Er, Yb)

A series of heterometallic carboxylate 1D polymers of the general formula [Ln^IIICd₂(piv)₇(H₂O)₂]_n·nMeCN (Ln^III = Sm (1), Eu (2), Tb (3), Dy (4), Ho (5), Er (6), Yb (7); piv = anion of trimethylacetic acid) was synthesized and structurally characterized. The use of Cd^II instead of Zn^II under similar synthetic conditions resulted in the formation of 1D polymers, in contrast to molecular trinuclear complexes with Ln^IIIZn₂ cores. All complexes 1–7 are isostructural. The luminescent emission and excitation spectra for 2–4 have been studied, the luminescence decay kinetics for 2 and 3 was measured. Magnetic properties of the complexes 3–5 and 7 have been studied; 4 and 7 exhibited the properties of field-induced single-molecule magnets in an applied external magnetic field. Magnetic properties of 4 and 7 were modelled using results of SA-CASSCF/SO-RASSI calculations and SINGLE_ANISO procedure. Based on the analysis of the magnetization relaxation and the results of ab initio calculations, it was found that relaxation in 4 predominantly occurred by the sum of the Raman and QTM mechanisms, and by the sum of the direct and Raman mechanisms in the case of 7.

Molecular and Polymer Ln2M2 (Ln = Eu, Gd, Tb, Dy; M = Zn, Cd) Complexes with Pentafluorobenzoate Anions: The Role of Temperature and Stacking Effects in the Structure; Magnetic and Luminescent Properties

Varying the temperature of the reaction of [{Cd(pfb)(H2O)4}+n·n(pfb)-], [Ln2(pfb)6(H2O)8]·H2O (Hpfb = pentafluorobenzoic acid), and 1,10-phenanthroline (phen) in MeCN followed by crystallization resulted in the isolation of two type of products: 1D-polymers [LnCd(pfb)5(phen)]n·1.5nMeCN (Ln = Eu (I), Gd (II), Tb (III), Dy (IV)) which were isolated at 25 °C, and molecular compounds [Tb2Cd2(pfb)10(phen)2] (V) formed at 75 °C. The transition from a molecular to a polymer structure becomes possible because of intra- and intermolecular interactions between the aromatic cycles of phen and pfb from neighboring tetranuclear Ln2Cd2 fragments. Replacement of cadmium with zinc in the reaction resulted in molecular compounds Ln2Zn2 [Ln2Zn2(pfb)10(phen)2]·4MeCN (Ln = Eu (VI), Tb (VIII), Dy (IX)) and [Gd2Zn2(pfb)10(H2O)2(phen)2]·4MeCN (VII). A new molecular EuCd complex [Eu2Cd2(pfb)10(phen)4]·4MeCN (X)] was isolated from a mixture of cadmium, zinc, and europium pentafluorobenzoates (Cd:Zn:Ln = 1:1:2). Complexes II-IV, VII and IX exhibit magnetic relaxation at liquid helium temperatures in nonzero magnetic fields. Luminescent studies revealed a bright luminescence of complexes with europium(III) and terbium(III) ions.

Some aspects of the formation and structural features of low nuclearity heterometallic carboxylates

Heterometallic carboxylate complexes are of paramount interest in pure and applied coordination chemistry. Despite that plurality of such type compounds have been published to date, synthetic aspects of their chemistry often remain in the shadow of intriguing physical properties manifesting by these species. Present review summarizes reliable data on direct synthesis of low nuclearity molecular compounds as well as coordination polymers on their base with carboxylate-bridged {M2Mg} (M = Co2+, Ni2+, Cd2+), {M2Li2} (M = Co2+, Ni2+, Zn2+, VO2+), {M2Ln2} and {M2Ln} (M = Cu2+, Zn2+, Co2+) metal cores. Structural features and stabilization factors are considered and principal outcomes are confirmed by quantum-chemical calculations. Particular attention is paid to consideration of ligand-exchange reactions that allow controllable modification of heterometallic metal core under mild conditions giving diverse molecular complexes with modified ligand environment or Metal-Organic Frameworks with permanent porosity.