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In this work we report the synthesis, structural characterization and magnetic properties of a family of butterfly complexes {Cr2Ln2} with Ln = Tb (4), Ho (5), Er (6), Tm (7) and Yb (8), extending the family of previously reported isostructural compounds with Gd (1), Dy (2) and Y (3). As in 1 and 2, an anti-ferromagnetic Cr(III)–Ln(III) exchange interaction is found. For oblate ions 4 and 5, SMM behavior with a purely Orbach relaxation mechanism is observed with thermal barriers of 38 cm−1 (4) and 32 cm−1 (5). Complex 4 displays hysteresis opening up to 2.4 K with loss of magnetization at zero field. The prolate complex ions 6 and 7 are field-induced SMM's with dominant Orbach, direct and QTM relaxation mechanisms. Compound 8 did not show SMM properties. [ABSTRACT FROM AUTHOR]

We present the synthesis of two new novel tetradentate ligands based on 1,3,4-oxadiazole, 2-(2-pyridyl)-5-[N,N-bis(2-pyridylmethyl)aminomethyl]-1,3,4-oxadiazole (LTetraPy–ODA) and 2-(2-phenyl)-5-[N,N-bis(2-pyridylmethyl)aminomethyl]-1,3,4-oxadiazole (LTetraPh–ODA). The ligands were used to prepare six mononuclear complexes [FeII(LTetraPy–ODA)(NCE)] (C1–C3) and [FeII(LTetraPh–ODA)(NCE)] (C4–C6) where E = S, Se or BH3. In addition, the ligand LTetraPy–ODA was employed in the synthesis of a new di-nuclear complex [Fe II2 (LTetraPh)](ClO4)4·1 CH3NO2·1.5 H2O (C7). Characterization of all complexes was carried out using single-crystal X-ray crystallography, elemental analysis, and infrared spectroscopy. Magnetic susceptibility measurements, performed in the temperature range of 2–300 K using a SQUID magnetometer, revealed spin crossover behaviour exclusively in the mononuclear complexes C3 and C6, in which two monodentate NCBH3− co-ligands coordinate. The presence of the lattice solvent was found to be crucial to the spin transition property, with complex C3 exhibiting a switching temperature (T1/2) of approximately 165 K and C6 approximately 194 K. The other four mononuclear complexes C1, C2, C4, C5, as well as the dinuclear complex C7 are locked in the high spin state over the measured temperature range. Density Functional Theory (DFT) calculations were performed on complexes C1–C6 to rationalise the observed magnetic behaviour, demonstrating the significant effect of the NCS−, NCSe− and NCBH3− co-ligands ligands on the spin-crossover behaviour of the [FeII(L)(NCE)] complexes. [ABSTRACT FROM AUTHOR]

The complex {Na2(H2O)8[GdCu5(GlyHA)5(H2O)4L]2}L2 ⋅ 2.5DMF ⋅ 10.5H2O (1, where GlyHA2−= glycinehydroxamate, L2−= 4,4′‐bis(2‐sulfonatostyryl)biphenyl) was obtained as the outcome of the metathesis reaction of previously reported [GdCu5(GlyHA)5(CO3)(NO3)(H2O)5] ⋅ 3.5H2O with an excess of the disulfonate's sodium salt. X‐Ray analysis of 1 shows a dimeric structure in which 15‐metallacrown‐5 units {GdCu5}3+ are arranged in an "edge‐to‐edge" manner by way of two linking disulfonates, L2−. Magnetic studies of polycrystalline 1 over a temperature range of 2–300 K revealed both Gd‐Cu ferromagnetic and Cu‐Cu antiferromagnetic interactions within the metallacrown unit. Experimental χMT vs. T data for 1 were fitted using different theoretical models. A two‐J model, which takes into account both exchange interactions between adjacent copper(II) ions and the Gd‐Cu exchange interactions allows fitting of the χMT vs. T data in the whole temperature range. The values obtained for the exchange parameters are in accord with previously reported parameters for Ln(III)‐Cu(II) 15‐metallacrowns‐5. The 240 GHz powder EPR spectra for 1 were recorded between 30 and 150 K. [ABSTRACT FROM AUTHOR]

We report the multi-step synthesis of the tetradentate 2-(naphthalen-2-yl)-5-[N,N-bis(2-pyridylmethyl)aminomethyl]-1,3,4-oxadiazole ligand (LTetra-ODA) along with its corresponding [FeII(LTetra-ODA)(NCBH3)2]·1.5CH3OH (C1) complex, which is the first mononuclear 1,3,4-oxadiazole based Fe(II) spin crossover (SCO) complex, and its zinc analogue [ZnII(LTetra-ODA)(NCBH3)2]·0.5H2O (C2). The spin transition is followed by variable temperature (VT-) X-ray crystallography of [Fe(LTetra-ODA)(NCBH3)2]·1.5CH3OH (C1) at 120 and 220 K. The magnetic susceptibility measurements on the bulk sample recorded from 2 to 300 K show that the complex exhibits a complete abrupt reversible spin transition with a T1/2 of 207 K. The loss of the lattice solvent methanol shifts the T1/2 slightly to around 210 K. The spin transition in solution for [Fe(LTetra-ODA)(NCBH3)2]·1.5CH3OH (C1) was followed using the VT-1H-NMR Evans method in CD3CN, with a T1/2 of 357 K. Solid state VT luminescence studies provide some preliminary evidence of interplay of luminescence and spin transition in the [Fe(LTetra-ODA)(NCBH3)2]·1.5CH3OH (C1) complex. [ABSTRACT FROM AUTHOR]