Gaining Insights into the Interplay between Optical and Magnetic Properties in Photoexcited Coordination Compounds

We describe early and recent advances in the fascinating field of combined magnetic and optical properties of inorganic coordination compounds and in particular of 3d-4f single molecule magnets. We cover various applied techniques which allow for the correlation of results obtained in the frequency and time domain in order to highlight the specific properties of these compounds and the future challenges towards multidimensional spectroscopic tools. An important point is to understand the details of the interplay of magnetic and optical properties through performing time-resolved studies in the presence of external fields especially magnetic ones. This will enable further exploration of this fundamental interactions i. e. the two components of electromagnetic radiation influencing optical properties.

Structural determinations and magnetic properties of a "chiral at metal" complex and its resulting [Cu-Ln]2 compounds

A chiral trianionic ligand possessing one amide, one imine, two phenol functions and one asymmetric carbon atom into its diamino chain reacts with Cu^II ions to yield anionic [LCu]^- units that crystallize in a non-centrosymmetric space group as infinite 1D zig-zag chains in which a transmission of chirality to the Cu^II ion is effective. The distorted square planar environment of the Cu^II ion is large enough to induce the presence of a stereogenic Cu^II centre. Further reaction with Ln^III ions in presence of ancillary ligands does not preserve such an arrangement but yields a tetranuclear complex made of two [LCu-Ln] units in a head-to-tail position. The tetranuclear [LCu-Ln]₂ complexes made with the racemic and chiral LCu units crystallize in different space groups, so that racemization does not occur. The structural determinations confirm that a symmetry centre is present in the two structures, except for the methyl groups linked to the chiral carbon atoms, which appear as disordered in the (S-S) tetranuclear entity. Such an arrangement implies a conformation change of the diamino chain linked to the Cu^II ion in one [LCu-Ln] unit of the (S-S) entity, and cancels any chirality contribution of the Cu^II ions, as in the meso compound. Ferromagnetic Cu-Ln interactions, resulting from an alternate distribution of the Cu^II and Ln^III ions, are the only ones to be active. Eventually the micro-Squid studies confirm that the hysteresis loops of the corresponding racemate and chiral tetranuclear [LCu-Dy]₂ entities are slightly different.

Carboxylate-Decorated Aggregation of Octanuclear Co4Ln4 (Ln = Dy, Ho, Yb) Complexes from Ligand-Controlled Hydrolysis: Synthesis, Structures, and Magnetic Properties

One-pot reactions of an asymmetric carboxy-ether-phenol based Schiff base H₂L (2-((2-hydroxy-3-methoxybenzylidene)amino)benzoic acid) with selected Ln(NO₃)₃·nH₂O and [Co₂(μ-OH₂)(O₂CCMe₃)₄(HO₂CCMe₃)₄] (Co₂-Piv) in basic MeOH medium resulted in a family of three octanuclear complexes, [Co^II₄Ln^III₄L₄(μ_1,3-Piv)₄(μ_1,1,3-Piv)₂(η¹-Piv)₂(μ₃-OH)₄(MeOH)₂]·mMeOH·nH₂O (Ln = Dy; m = 3, n = 1 (1), Ho; m = 4, n = 0 (2), Yb; m = 3, n = 1 (3)). The coordination aggregates thus obtained were nicely sustained by four ligand anions and eight externally added carboxylate anions showing three different modes of intermetallic connectivity. The options for incorporating different 4f ions in an investigative synthesis, without altering the resulting intermetallic core structure, were successful for the three representative examples. Single-crystal X-ray diffraction studies revealed that the compounds are isostructural and built from two initially formed partial dicubane-type Co₂Ln₂L₂ units. In each of the tetranuclear parts, the metal ion centers are held together by two L^2-, two μ₃-HO^-, three Piv^- bridges, one terminal Piv^-, and one terminal MeOH. Four carboxylate ends of four L^2- units are responsible for connecting two Co₂Ln₂ units into octanuclear structures. The unique distortion around the Co^II centers is achieved from the facile coordination of bigger 4f ions to the adjacent hard OO sites. The distortion is further maintained by the presence of terminal COO^- groups from L^2-. The dc magnetic susceptibility data revealed ferromagnetic coupling between the Co^II and Ln^III centers within the series, whereas the ac magnetic susceptibility measurements identified only 1, having a highly anisotropic Dy^III ion, as a single-molecule magnet in the absence of any external magnetic field, with an energy barrier U_eff of 12.5 K.

A family of planar hexanuclear CoLn clusters with lucanidae-like arrangement and single-molecule magnet behavior

A family of planar hexanuclear CoLn clusters with the hydroxyl and nitrogen rich ligand 2-[bis(pyridin-2-ylmethyl) amino]-2-(hydroxymethyl)propane-1,3-diol (H₃L), formulated as [Co₄Ln₂(μ₃-O)₂(μ-N₃)₂(OH)₂(H₂O)₂(HL)₄]·(CH₃CO₂)₂·20H₂O [Ln = Dy (1), Gd (2), Tb (3), Eu (4) and Ho (5)], have been synthesized and structurally characterized. They are isomorphous and feature a lucanidae-like arrangement. They are the first examples of 3d-4f clusters with the H₃L ligand. In addition, the magnetic properties of 1-5 have been investigated and the single-molecule magnet (SMM) behaviour is observed for 1.

Syntheses, Structures, and Magnetic Properties of a Series of Heterotri-, Tetra- and Pentanuclear LnIII⁻CoII Compounds

Three types of Ln(III)⁻Co(II) heterometallic compounds, LnCo₂(L1)₇(bipy)₂ (Ln = Pr-1, Eu-2, Sm-3, Gd-4, Tb-5, Dy-6) (L1 = 4-chlorobenzoate, bipy = 2,2'-bipyridine), Ln₂Co₂(L₂)10(bipy)₂ (Ln = Sm-7, Gd-8, Tb-9, Dy-10, Ho-11, Er-12, Yb-13), (L2 = 2,4-dichlorobenzoate, bipy = 2,2'-bipyridine, phen = 1,10-phenanthroline), and Ln₂Co₃(L1)12(bipy)₂ (Ln = Ho-14, Er-15, Yb-16), were synthesized under hydrothermal conditions and characterized by single crystal X-ray diffraction, IR spectroscopy and magnetic measurements. Structural analyses revealed that 14⁻16 take on a unique linear pentanuclear structural motif. Interestingly, the Ho-containing compound 14 exhibits magnetic relaxation behavior.

Slow magnetic relaxation in Cu(ii)–Eu(iii) and Cu(ii)–La(iii) complexes

A dinuclear [(H₂O)Cu(HLN₂O₂)Eu(NO₃)₃] complex exhibits paramagnetic behaviour with S = 1/2 ground state. At low temperature it displays slow magnetic relaxation that is supported by a small external magnetic field.

A W-Shaped Ga-Dy-Dy-Dy-Ga Cluster: Synthesis, Characterization, and Magnetic Properties

A W-shaped {Ga-Dy-Dy-Dy-Ga} coordination cluster, [Ga₂ Dy₃ (L)₆ (MeO)₂ (MeOH)₃ ]⋅NO₃ ⋅7 MeOH (1) with H₂ L, (E)-2-(2-hydroxy-3-methoxy-benzylideneamino)phenol was synthesized, characterized, and the magnetic properties investigated. The magnetic measurements indicate that the compound shows single-molecule magnet (SMM) behavior under zero dc field. This suggests that the combination of Ga^III ions and Dy^III ions (4 f) is a successful strategy to assemble SMM clusters. The combination of these metal ions also offers prospects in dual functionality therapeutics for medical applications.

Butterfly M2 IIIEr2 (MIII = Fe and Al) SMMs: Synthesis, Characterization, and Magnetic Properties

The reaction of N-(2-pyridylmethyl)iminodiethanol (H₂L, pmide), FeCl₂·4H₂O or AlCl₃·6H₂O with ErCl₃·6H₂O and p-Me-PhCO₂H in the ratio of 2:1:1:4 in the presence of Et₃N in MeOH and MeCN yielded compounds [Fe₂Er₂(μ₃-OH)₂(pmide)₂(p-Me-PhCO₂)₆]·2MeCN (1) and [Al₂Er₂(μ₃-OH)₂(pmide)₂(p-Me-PhCO₂)₆]·2MeCN (2). These two complexes are isostructural, possessing a planar butterfly motif with the Er^III ions in the wingtip positions. Both compounds show single molecule magnet (SMM) behavior. For the [Al₂Er₂] compound, the slow relaxation of the magnetization under zero applied direct current (dc) field does not show maxima, but the relaxation processes could be analyzed using an applied dc field of 1000 Oe. In-depth alternating current measurements under different dc fields on the [Fe₂Er₂] compound reveals that the Fe-Fe and Fe-Er interactions speed up the relaxation and decrease the energy barrier height of the SMM in comparison with the [Al₂Er₂] case.

NiII–LnIII complexes with o-vanillin as the main ligand: syntheses, structures, magnetic and magnetocaloric properties

ortho-Vanillin yields three types of heteronuclear Ni^II–Ln^III complexes, ranging from dinuclear to tetranuclear defect dicubane complexes.

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.

The ferromagnetic [Ln2Co6] heterometallic complexes

Four 3d–4f [Ln₂Co₆] complexes were fabricated. [Dy₂Co₆] (1) and [Ho₂Co₆] (2) displayed ferromagnetic coupling, and [Dy₂Co₆] (1) exhibited slow magnetic relaxation.

Nine self-assembled nickel(ii)–lanthanide(iii) heterometallic complexes constructed from a Salamo-type bisoxime and bearing a N- or O-donor auxiliary ligand: syntheses, structures and magnetic properties

Nine Ni(ii)–Ln(iii) complexes were prepared using 3-MeOsalamo and structurally characterized, and their magnetic properties were studied.

Linking Cr₃ triangles through phosphonates and lanthanides: synthetic, structural, magnetic and EPR studies

The preparation and structural characterisation of five 3d-4f mixed metal phosphonate cages with general formula [Cr(III)6Ln(III)2(μ3-O)2(H2O)2(O3P(t)Bu)4(O2C(t)Bu)12(HO(i)Bu)2((i)PrNH2)2] where Ln(III) = La, 1; Tb, 3; Dy, 4; Ho, 5 and [Cr(III)6Gd(III)2(μ3-O)2(H2O)2(O3P(t)Bu)4(O2C(t)Bu)12(HO(i)Bu)4] (2) are reported. The structure contains two oxo-centred {Cr3} triangles, bridged by phosphonates and lanthanides. The magnetic behaviour of 1 has been modelled as two non-interacting isosceles triangles, involving two antiferromagnetic interactions (J1 = -8.8 cm(-1)) with a smaller ferromagnetic interaction for the unique edge of the triangle (J2 = +1.3 cm(-1)) giving an isolated S = 3/2 ground state per triangle. The quartet ground state has been proven through simulation of electron paramagnetic resonance (EPR) spectra obtained at the X- and Q-band. EPR simulations have also resulted in the introduction of small single-ion Zero Field Splitting (ZFS) parameters D = ±0.19 cm(-1) and rhombic term E = ±0.02 cm(-1), which are consistent with strong exchange limit calculations for an isolated S = 3/2 (D = ±0.22 and E = ±0.018 cm(-1)).

Experimental and theoretical investigations of four 3d–4f butterfly single-molecule magnets

Experimental and theoretical investigations of four 3d–4f defect-dicubane single-molecule magnets.

The exceptionally rich coordination chemistry generated by Schiff-base ligands derived from o-vanillin

Recent and relevant examples of homo- and heterometallic complexes generated by Schiff base ligands derived from o-vanillin, as well as their properties, are discussed.

Cu(ii)–Dy(iii) and Co(iii)–Dy(iii) based single molecule magnets with multiple slow magnetic relaxation processes in the Cu(ii)–Dy(iii) complex

Two Cu^II–Dy^III and Co^III–Dy^III dinuclear complexes of a Schiff base ligand (H₃L) exhibit single-molecule magnetic behaviour with multiple slow magnetic relaxation processes for the former.

Modulating the magnetic properties by structural modification in a family of Co-Ln (Ln = Gd, Dy) molecular aggregates

Two types of 3d–4f cages are reported where the Gd analogues show significant magnetic refrigeration and the Dy containing compounds display SMM behaviour.

Assembly of heterobimetallic NiII–LnIII (LnIII = DyIII, TbIII, GdIII, HoIII, ErIII, YIII) complexes using a ferrocene ligand: slow relaxation of the magnetization in DyIII, TbIII and HoIII analogues

Structure and characterization of a new family of dinuclear 3d–4f heterobimetallic complexes [LNi(H₂O)(μ-OAc)Ln(NO₃)₂]·CH₃CN; {Ln = Dy^III (1), Tb^III (2), Ho^III (3), Gd^III (4), Er^III (5), Y^III (6)} using a ferrocene-based compartmental ligand H₂L.