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An in situ hydrolysis of the P–Cl bonds of the carbophosphazene [{NC(NMe2)}2{NPCl2}] (LPCl2) in the presence of hydrated lanthanide(III) nitrates in a dichloromethane and methanol (2 : 1) solvent mixture afforded a series of novel 1D coordination polymers: [{Ln(LHPO2)3(NO3)2(CH3OH)(H2O)} (Cl)]n {where Ln(III) = Gd (1), Tb (2), Dy (3), or Er (4) and LHPO2 is the hydrolyzed carbophosphazene (LPCl2) ligand}. X-ray crystallographic analysis revealed that complexes 1–4 are isostructural and crystallized in the monoclinic crystal system having P21/c space group. The coordination polymers are formed because of the involvement of the geminal P(O)(OH) moieties of the carbophosphazene ligand. Each lanthanide(III) ion is 9-coordinate (9O) in a distorted muffin geometry. Magnetic measurements revealed that both DyIII and ErIII analogues exhibit field-induced single-molecule magnet (SMM) behavior at 0.8 kOe and 2.2 k Oe, respectively. At such dc fields, the dynamic magnetic susceptibility displays complex behavior with a triple magnetic relaxation contribution for 3, while two contributions were identified for 4. The observed static and dynamic magnetic behavior for complexes 1–4 were further rationalized with the aid of BS-DFT and CASSCF/SO-RASSI/SINGLE_ANISO calculations. [ABSTRACT FROM AUTHOR]

A series of heterotetranuclear complexes [CoII2Ln2(HL)4(OAc)3(H2O)2]·(NO3)3 (where LnIII = Ho (1), Er (2) or Yb (3)) reported with a Schiff base (2-methoxy-6-[(E)-2′-hydroxymethyl-phenyliminomethyl]-phenol) ligand. The X-ray diffraction and structural solution confirmed the isostructural identity of 1 and 3. Complexes 1 and 3 were crystallized in a monoclinic crystal system having a C2/c space group, while complex 2 lacked X-ray quality crystals. The direct current (dc) magnetic measurements on complexes 1–3 indicate dominant intramolecular ferromagnetic interactions. The CASSCF/SO-RASSI/SINGLE_ANISO calculations followed by POLY_ANISO simulations were performed to understand the electronic structure, nature and strength of the CoII–LnIII and LnIII–LnIII magnetic exchange interactions, using the Molcas 8.0 program. To verify the nature of CoII–LnIII magnetic interactions, BS-DFT calculations were performed. The sign and the magnitude of the estimated JCo–Ln values show weak but dominant intramolecular ferromagnetic interactions between CoII and LnIII metal ions. In contrast, JLn–Ln values show the weak antiferromagnetic interactions between LnIII ions in complexes 1–3. [ABSTRACT FROM AUTHOR]

A series of Schiff base LH ((E)-2-((pyridin-2-ylmethylene)amino)phenol) supported phenoxo bridged symmetric [Dy2(L)2(hfac)4] (1), [Dy2(L)2(tfac)4] (2) and asymmetric [Dy2(L)2(thd)3(NO3)]·1.5H2O (3) binuclear complexes were isolated using differently substituted β-diketonate co-ligands (Hhfac = hexafluoroacetylacetonate, Htfac = trifluoroacetylacetonate, and Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione). In all the three complexes 1–3, the two LH ligands provide phenoxo bridging and N-donor atoms. The {Dy2(μ2-O)2} magnetic core structures with LH ligands are found to be the same in 1–3 while the dissimilar functionalities of the axially coordinated different β-diketonate co-ligands play a crucial role in modulating the magnetic anisotropy of individual DyIII sites and magnetic exchange between them. The experimental static magnetic behaviour suggests the presence of intramolecular antiferromagnetic interactions in all the three complexes 1–3. The strength of the magnetic exchange coupling decreases with increasing magnetic anisotropy of individual DyIII ions from complex 1 to complex 3 and simultaneously their zero-field slow magnetic relaxation behaviors were found to increase with effective energy barriers (ΔE/kB) of 9.04 K, 24.06 K and 25.65 K, respectively. Furthermore, the DFT and ab initio theoretical calculations performed on the X-ray structures of complexes 1–3 support our experimental findings. [ABSTRACT FROM AUTHOR]

The tetranuclear Ni II2 Ln III2 complexes, [{L′2{Ni(MeOH)(μ-OAc)}2(μ3-MeO)2Ln2}, LnIII = YIII (1), GdIII (2), TbIII (3), and DyIII (4)], were prepared using a Schiff base ligand, H3L [H3L = 3-{(2-hydroxy-3-methoxybenzylidene)amino}-2-(2-hydroxy-3-methoxyphenyl)-2,3-dihydroquinazolin-4(1H)-one, where {L′}3− is the deprotonated open structure of H3L]. X-ray crystallographic analysis of 1–4 revealed that all the complexes crystallized in the orthorhombic (Pbcn) space group, and possessed an isostructural tetranuclear butterfly or defect dicubane like core. Direct current magnetic susceptibility measurements performed on 2–4 revealed that all these complexes show an intramolecular ferromagnetic exchange coupling. Well resolved zero-field out-of-phase signals in ac magnetic susceptibility measurements were observed only in the case of 3 (Ueff = 13.4 K; τ0 = 4.1(7) × 10−7 s). This was attributed to the comparatively strong NiII–TbIII magnetic exchange coupling. DFT and ab initio calculations were carried out on 1–4 to ascertain the nature of the ferromagnetic NiII–LnIII (JNi–Ln) and LnIII–LnIII (JLn–Ln) interactions. Magnetic anisotropy and magnetic relaxation mechanisms were discussed in detail for 3 and 4. Theoretical studies provide a rationale for the slow relaxation of magnetization in 3. [ABSTRACT FROM AUTHOR]

We hereby report a series of near-linear trinuclear [Zn2LnIII(HL)4(CH3COO)]·(NO3)2 (where LnIII = La (1-La), Ce (2-Ce), Nd (3-Nd), Sm (4-Sm), Tb (5-Tb), and Dy (6-Dy)) complexes with Schiff base ligand (H2L). Magnetization relaxation dynamic studies on complexes 2-Ce, 5-Tb, and 6-Dy reveal the existence of well resolved frequency dependent zero-field out-of-phase χ′′M signals, which is an indicator of a typical single-ion magnet behavior observed only for complex 6-Dy with Ueff = 43.7 K (τ0 = 2.42 × 10−6 s). The presence of two Zn(II) ions near the coordination geometry of Dy(III) ion in 6-Dy is likely to keep the first excited mJ levels significantly away from the ground state mJ level and is responsible for the observation of zero field slow magnetic relaxation behavior. The data collected in the presence of a magnetic field of Hdc = 2 kOe enhances the energy barrier by two-fold (88.63 K, τ0 = 1.36 × 10−7 s) in 6-Dy, suggesting the presence of QTM at zero field along with other under barrier relaxations, such as the Raman process. On the other hand, complex 2-Ce shows field induced slow relaxation of magnetization behavior with an effective energy barrier of 12.24 K (τ0 = 1.89 × 10−4 s). The CASSCF/SO-RASSI/SINGLE_ANISO based ab initio calculations using MOLCAS 8.0 code further rationalized our experimentally observed magnetization dynamics. [ABSTRACT FROM AUTHOR]

We herein report a series of near-linear trinuclear complexes [Co2Ln(HL)4(NO3)](NO3)2 (where HL = (2-methoxy-6-[(E)-2′-hydroxymethyl-phenyliminomethyl]-phenolate) with Ln(III) = La (1), Ce (2), Pr (3)). For the comparative study, we have also included the recently reported analogous complexes of Gd(III), Tb(III), and Dy(III) (complexes 4–6) with the same H2L ligand. The experimental nature of the dc magnetic susceptibilities profile and an empirical approach revealed that the magnetic exchange interaction between Co(II) and Ln(III) having <4f7 (complexes 2 and 3) is antiferromagnetic while the dominant interaction between Co(II) and Ln(III) having ≥4f7 (complexes 4–6) is ferromagnetic. Dynamic magnetic relaxation studies on complexes 1–3 revealed the field induced single-molecule magnetic (SMM) behavior of 1 and 3 with effective energy barriers of 10.65 K and 15.03 K respectively, for magnetic relaxation. To the best of our knowledge, 3d-Pr(III) based zero or field induced SMMs have not been reported to date. CASSCF/SO-RASSI/SINGLE_ANISO based ab initio calculations on the X-ray structures of complexes 1–6, followed by POLY_ANISO simulations, estimated the magnetic exchange coupling constants JCo–Ln and JCo–Co and also rationalized our experimental findings for the dynamic magnetic properties. [ABSTRACT FROM AUTHOR]

A series of dinuclear lanthanide(III) complexes having general formulae [Ln2L2(thd)4] ⋅ 2CH3CN {Ln=DyIII(1), TbIII(2), GdIII(3), ErIII(4)} were successfully synthesized using Schiff base (E)‐2‐((pyridin‐2‐ylmethylene)amino)phenol (LH) and co‐ligand 2,2,6,6‐Tetramethyl‐3,5‐heptanedione (Hthd). The single crystal XRD data shows that complexes possess a dinuclear planar [Ln2(μ2‐O)2]4+ core where phenolate oxygen atoms act as bridges between the two LnIII ions, and that the coordination sphere of LnIII with eight coordination has distorted trigonal dodecahedron geometry. The magnetic analysis shows complex 1 is a single molecule magnet having a zero‐field effective energy barrier (Ueff) of 54.02 K and relaxation time of τo=4.45×10−6 s. Field‐induced SMM behavior has been observed for 4 with an effective energy barrier of 26.9 K and τ0=2.4×10−9 s. CASSCF+RASSI‐SO calculations on 1, 2 and 4 provide deep insight regarding the electronic structure and single‐ion anisotropy of lanthanide ions. Further, using state‐of‐the‐art ab initio calculations, the nature of magnetic anisotropy and magnetic exchange interaction between the LnIII centers is analyzed to shed light on the magnetic dynamics of all the complexes 1–4. [ABSTRACT FROM AUTHOR]

The reaction of a bulky acetyl acetone ligand 1,3-dimesitylpropane-1,3-dione (MesacacH) with hydrated lanthanide chlorides in the presence of tetramethylammonium hydroxide afforded a new family of neutral mononuclear LnIII complexes [Ln(Mesacac)3(DMF)] (Ln = Dy (1); Tb (2); Y0.91Dy0.09 (3); and Er (4)). The molecular structures of these complexes were confirmed by single crystal X-ray diffraction studies. The coordination geometries of the LnIII centre were analysed by SHAPE analysis which revealed a capped octahedral geometry in 1–4. Photoluminescence studies showed ligand-sensitized green emissions for 2 with an appreciable quantum yield of 0.83%. Static (dc) and dynamic (ac) magnetic studies of complexes 1 and 3 were performed. The dynamic magnetic study revealed that complex 1 exhibits zero-field slow relaxation of the magnetization without showing a clear maximum in the out-of-phase ac susceptibility plots. However, magnetic dilution of 1 with the YIII metal ion (complex 3) and/or the application of a dc magnetic field induces a strong frequency dependence of the ac susceptibility signals with χ′′M peaks in the 3–10 K temperature range, thus supporting field-induced SMM behaviour of 1. The relaxation process takes place through a combination of the Orbach and Raman mechanisms. The fitting of the temperature dependence of the relaxation time to the equation τ−1 = τ0−1 exp(–Ueff/kBT) + BTn, allows the extraction of the effective energy barrier Ueff/kB = 70 K (48.7 cm−1) and pre-exponential parameter of τ0 = 2.7 × 10−7 s for the Orbach mechanism (first term) and the parameters B = 0.04 s−1 K−n and n = 6.11, for the Raman mechanism (second term). [ABSTRACT FROM AUTHOR]