Pentanuclear 3d–4f Heterometal Complexes of MII3LnIII2 (M = Ni, Cu, Zn and Ln = Nd, Gd, Tb) Combinations: Syntheses, Structures, Magnetism, and Photoluminescence Properties

Modulation of the magnetic and photophysical properties in 3d-4f and 4f-4f' heterobimetallic complexes involving a tetrathiafulvalene-based ligand

The reaction between the 2-(1-(2,6-di(pyrazol-1-yl)-4-methylpyridyl)-4,5-(4,5-bis(propylthio)-tetrathiafulvalenyl)-1H-benzimidazol-2-yl)-pyridine ligand (L), 1 equivalent of Ln(hfac)3·2H2O/Dy(tta)3·2H2O (hfac- = 1,1,1,5,5,5-hexafluoroacetylacetonate, tta- = 2-thenoyltrifluoroacetonate) and M(hfac)2·2H2O leads to the formation of heteroleptic 3d-4f dinuclear complexes of formula [MLn(hfac)5(L)]n (M(II) = Cd, Zn, Co, Mn, Ni and Ln(III) = Dy, Yb, Nd) and [ZnDy(tta)2(hfac)3(L)]·(CH2Cl2). Their X-ray structures reveal that the two coordination sites are occupied by one Ln(III) ion and one M(II) transition metal respectively. The M(II) ions are coordinated to the benzoimidazolylpyridine (bzip) moiety in a N2O4 coordination sphere, while the Ln(III) ions are coordinated to the 2,6-di(pyrazol-1-yl)-4-pyridine (dpp) moiety in a N3O6 surrounding. When Dy(III) ion is used a field-induced Single-Molecule Magnet (SMM) behavior is detected with a magnetic relaxation time slightly dependent to the nature of the vicinal divalent transition metal. On the other hand, when the Yb(III) is used, intense, moderated or quenched 2F5/2 → 2F7/2 NIR luminescence is observed when the Yb(III) ion is respectively associated with the Zn(II), Mn(II) and Ni(II)/Co(II) ion. The emission intensity can be modulated in function of the metal-to-ligand charge transfer and d-d transition intensities. The replacement of the divalent transition metal by a trivalent lanthanide leads to the formation of heteroleptic 4f-4f' dinuclear complexes of formula [Ln2-xLn'x(hfac)6(L)]·a(CH2Cl2)·b(C6H14) and [Dy1.11Nd0.89(tta)3(hfac)3(L)]. The coordination selectivity is based on the radius. Among the 4f-4f' series, the Dy(III) derivatives displayed such ion in N2O6 eight-coordinated sphere allowing the observation of SMM behavior. The three compounds [Dy1.21Nd0.79(hfac)6(L)]·2(CH2Cl2)·(C6H14), [Yb1.04Nd0.96(hfac)6(L)] and [YbPr(hfac)6(L)] displayed respectively Nd(III), modarated Yb(III) and intense Yb(III) NIR emissions.

Synergistic Experimental and Theoretical Studies of Luminescent-Magnetic Ln2Zn6 Clusters

The present work is part of our ongoing quest for developing functional inorganic complexes using unorthodox pyridyl-pyrazolyl-based ligands. Accordingly, we report herein the synthesis, characterization, and luminescence and magnetic properties of four 3d-4f mixed-metal complexes with a general core of Ln₂Zn₆ (Ln = Dy, Gd, Tb, and Eu). In stark contrast to the popular wisdom of using a compartmental ligand with separate islands of hard and soft coordinating sites for selective coordination, we have vindicated our approach of using a ligand with overcrowded N-coordinating sites that show equal efficiency with both 4f and 3d metals toward multinuclear cage-cluster formation. The encouraging red and green photolumiscent features of noncytotoxic Eu₂Zn₆ and Tb₂Zn₆ complexes along with their existence in nanoscale dimension have been exploited with live-cell confocal microscopy imaging of human breast adenocarcinoma (MCF7) cells. The magnetic features of the Dy₂Zn₆ complex confirm the single-molecule-magnet behavior with befitting frequency- and temperature-dependent out-of-phase signals along with an U_eff value of ∼5 K and a relaxation time of 8.52 × 10^-6 s. The Gd₂Zn₆ complex, on the other hand, shows cryogenic magnetic refrigeration with an entropy change of 11.25 J kg^-1 K^-1 at a magnetic field of 7 T and at 2 K. Another important aspect of this work reflects the excellent agreement between the experimental results and theoretical calculations. The theoretical studies carried out using the broken-symmetry density functional theory, ORCA suite of programs, and MOLCAS calculations using the complete-active-space self-consistent-field method show an excellent synergism with the experimentally measured magnetic and spectroscopic data.

Crystal structure of a TbIII-CuII glycine-hydroxamate 15-metallacrown-5 sulfate complex

The core of the title complex, bis-[hexa-aqua-hemi-aqua-penta-kis-(μ3-glycine-hydroxamato)sulfato-penta-copper(II)terbium(III)] sulfate hexa-hydrate, [TbCu5(SO4)(GlyHA)5(H2O)6.5]2(SO4)·6H2O (1), which belongs to the 15-metalla-crown-5 family, consists of five glycine-hydroxamate dianions (GlyHA2-; C2H4N2O2) and five copper(II) ions linked together forming a metallamacrocyclic moiety. The terbium(III) ion is connected to the centre of the metallamacrocycle through five hydroxamate oxygen atoms. The coordination environment of the Tb3+ ion is completed to an octa-coordination level by oxygen atoms of a bidentate sulfate and an apically coordinated water mol-ecule, while the copper(II) atoms are square-planar, penta- or hexa-coordinate due to the apical coordination of water mol-ecules. Continuous shape calculations indicate that the coordination polyhedron of the Tb3+ ion in 1 is best described as square anti-prismatic. The positive charge of each pair of [TbCu5(GlyHA)5(H2O)6.5(SO4)]2 2+ fragments is compensated by a non-coordinated sulfate anion, which is located on an inversion center with 1:1 disordered oxygen atoms. Complex 1 is isomorphous with the previously reported compounds [LnCu5(GlyHA)5(SO4)(H2O)6.5]2(SO4), where Ln III = Pr, Nd, Sm, Eu, Gd, Dy and Ho.

Hetero-bimetallic Lanthanide-Coinage Metal Compounds Featuring Possible Metal-Metal Interactions in the Excited State

Heterometallic complexes, combining metals of the outer rims of the d-block, for example lanthanides(III) (Ln) and coinage metals(I) (M) are scarcely reported, synthetically challenging and highly interesting in terms of their interactions. In this context, we synthesized hetero-bimetallic Ln-M compounds ligated by the phosphine functionalized amidinate system (N,N'-bis[(2-diphenylphosphino)phenyl]formamidinate, "dpfam"). The resulting compounds [dpfam3 LnM][OTf] (Ln = La, Nd and M = Ag, Au) feature a close proximity of the two metal centres and were investigated experimentally by photoluminescence spectroscopy and quantum chemical calculations. The latter showed rare La-Au interactions for the first excited state.

Multifunctional ZnII–LnIII (Ln = Tb, Dy) complexes based on the amine-phenol ligand with field-induced slow magnetic relaxation, luminescence, and proton conduction

Two new isomorphic Zn^II–Ln^III–Zn^II trinuclear complexes based on the amine-phenol ligand have been prepared.

Magnetic relaxation in two chain-like Zn2Dy2 Schiff base coordination polymers bridged by tetraoxolene and its one-electron reduced radical

Two chain-like Zn–Dy anilate radical coordination polymers with Schiff base ligands show magnetic relaxation behaviors.

Zn2Ln2 complexes with carbonate bridges formed by the fixation of carbon dioxide in the atmosphere: single-molecule magnet behaviour and magnetocaloric effect

In the self-assembly process, CO₂ in the air is automatically fixed to Zn₂Ln₂ cluster molecular materials.

Synthesis, crystal structures and magnetic properties of a series of chair-like heterometallic [Fe4Ln2] (Ln = GdIII, DyIII, HoIII, and ErIII) complexes with mixed organic ligands

Four chair-like hexanuclear Fe-Ln complexes containing mixed organic ligands, namely, [Fe₄Ln₂{(py)₂CO₂}₄(pdm)₂(NO₃)₂(H₂O)₂Cl₄]·xCH₃CN·yH₂O (Ln = Gd^III (1, x = 1, y = 0), Dy^III (2, x = 1, y = 1), Ho^III (3, x = 0, y = 2), and Er^III (4, x = 1, y = 3); (py)₂CO₂H₂ = the gem-diol form of di-2-pyridyl ketone and pdmH₂ = 2,6-pyridinedimethanol) have been obtained by employing di-2-pyridyl ketone and 2,6-pyridinedimethanol reacting with FeCl₃ and Ln(NO₃)₃ in MeCN. The structures of 1-4 are similar to each other except for the number of lattice solvent molecules. Four Fe^III and two Ln^III in these complexes comprise a chair-like core with the "body" constructed by four Fe^III ions and the "end" constructed by two Ln^III ions. Among the four compounds, 2 shows field-induced single molecule magnet behavior as revealed by ac magnetic susceptibility studies, with the effective energy barrier and the pre-exponential factor of 22.07 K and 8.44 × 10^-7 s, respectively. Ab initio calculations indicated that, among 2_Dy, 3_Ho and 4_Er fragments, the energy gap between the lowest two spin-orbit states for 2_Dy is the largest, while the tunneling gap for 2 is the smallest. These might be the reasons for complex 2 exhibiting SMM behavior. Additionally, the orientations of the magnetic anisotropy of Dy^III in 2 were obtained by electrostatic calculations and ab initio calculations, both indicating that the directions of the main magnetic axis of Dy1 ions are almost aligned along Dy1-O5 (O5 from the pdm^2- ligand).

Both magnetic relaxation and luminescence of Zn2Dy2 cluster complexes regulated by the bis-imine chain in Schiff base ligands

The bis-imine bridge in Schiff base ligands has effects on the magnetic relaxation and luminescence of two Zn₂Dy₂ cluster complexes.

The role of 3d–4f exchange interaction in SMM behaviour and magnetic refrigeration of carbonato bridged CuII2LnIII2 (Ln = Dy, Tb and Gd) complexes of an unsymmetrical N2O4 donor ligand

The role of exchange interaction between Cu(ii) and Ln(iii) ions in SMM behaviour and magnetocaloric effects has been extensively investigated by both experimental and theoretical CASSCF/RASSI-SO/SINGLE_ANISO methods.

Synthesis and magneto-structural studies on a new family of carbonato bridged 3d–4f complexes featuring a [CoII3LnIII3(CO3)] (Ln = La, Gd, Tb, Dy and Ho) core: slow magnetic relaxation displayed by the cobalt(ii)–dysprosium(iii) analogue

A new series of carbonato-bridged complexes containing a CoII3LnIII3 core have been synthesized.

Details make the difference: a family of tetranuclear CuIIMnIII complexes with cube-like and double open cube-like cores

The "direct synthesis" approach, namely one-pot reaction of metal powders and ammonium salt with a methanol solution of a polydentate Schiff base (H₂L) formed in situ from salicylaldehyde and ethanolamine, has been successfully used for the preparation of the new heterometallic compounds [Cu₃Mn(L)₄(CH₃OH)₃]I₃ (1), [Cu₃Mn(L)₄(CH₃OH)₃(H₂O)]NCS·H₂O (2), [Cu₃Mn(L)₄(CH₃OH)(H₂O)_2.55]Br·0.45H₂O (3) and [Cu₃Mn(L)₄(H₂O)_3.4]BF₄·0.6H₂O (4). Crystallographic analysis revealed that 1-4 are based on the tetranuclear core {CuMn^III(μ₃-O)₄} where the metal centres are joined by the oxygen bridges of Schiff base ligands forming a cube-like arrangement. The novel heterometallic compound [Cu₃Mn(L)₄(CH₃OH)₃]₂[Mn(NCS)₄]·2CH₃OH (5) has been obtained by the "building block" approach using the reaction of [Cu(HL)₂] with manganese acetate and NH₄NCS in methanol. The crystal structure of 5 revealed the {CuMn^III(μ-O)₂(μ₃-O)₂} metal core which can be viewed as a double open cube. In spite of a similar {Cu₃MnO₄} atom set in the cores of 1-5, the complexes show rather different molecular structures and significantly differ by the number and combinations of coordinated CH₃OH/H₂O solvent molecules. Variable-temperature (2-300 K) magnetic susceptibility along with variable-field magnetization measurements of 1-5 showed a decrease of the effective magnetic moment value at low temperature, indicative of the antiferromagnetic coupling of medium size (-55 to -22 cm^-1). For these systems resembling a compressed prism the coupling constant in walls J₄ correlates with the averaged bonding angles in walls α: J₄vs. α develops approximately according to a straight line.

3d–4f heterometallic trinuclear complexes derived from amine-phenol tripodal ligands exhibiting magnetic and luminescent properties

The syntheses, crystal structures, and magnetic properties of a family of new 3d–4f heterometallic trinuclear complexes were investigated. Slow magnetic relaxation was observed for the Zn–Dy–Zn complex besides stronger fluorescent emissions.

Syntheses, crystal structures, and magnetic properties of a family of heterometallic octanuclear [Cu6Ln2] (Ln = Dy(iii), Tb(iii), Ho(iii), Er(iii), and Gd(iii)) complexes

Five novel [Cu₆Ln₂] complexes were synthesized, wherein Ln^III ions are seven-coordinate and coordinated by one triethanolamine and three di-2-pyridyl ketone ligands, without coordinated solvent molecules and small anions.

Four Salamo-type 3d–4f hetero-bimetallic [ZnIILnIII] complexes: syntheses, crystal structures, and luminescent and magnetic properties

A series of [Zn^IILn^III] complexes (Ln = Sm, Eu, Tb and Dy) are synthesized by Salamo-type ligand H₂L. Only [Zn^IISm^III] shows the characteristic transitions of Sm³⁺ ion, indicating the effective energy transfer between the ligand and Sm³⁺ ion.

Lanthanide-directed synthesis of luminescent self-assembly supramolecular structures and mechanically bonded systems from acyclic coordinating organic ligands

Herein some examples of the use of lanthanide ions (f-metal ions) to direct the synthesis of luminescent self-assembly systems (architectures) will be discussed. This area of lanthanide supramolecular chemistry is fast growing, thanks to the unique physical (magnetic and luminescent) and coordination properties of the lanthanides, which are often transferred to the resulting supermolecule. The emphasis herein will be on systems that are luminescent, and hence, generated by using either visibly emitting ions (such as Eu(III), Tb(III) and Sm(III)) or near infrared emitting ions (like Nd(III), Yb(III) and Er(III)), formed through the use of templating chemistry, by employing structurally simple ligands, possessing oxygen and nitrogen coordinating moieties. As the lanthanides have high coordination requirements, their use often allows for the formation of coordination compounds and supramolecular systems such as bundles, grids, helicates and interlocked molecules that are not synthetically accessible through the use of other commonly used templating ions such as transition metal ions. Hence, the use of the rare-earth metal ions can lead to the formation of unique and stable species in both solution and in the solid state, as well as functional and responsive structures.