Pankaj Kalita

Mononuclear Lanthanide Complexes: Energy-Barrier Enhancement by Ligand Substitution in Field-Induced DyIII SIMs

The sequential reaction of 2-((6-(hydroxymethyl)pyridin-2-yl)-methyleneamino)phenol (LH2), LnCl3·6H2O, and 1,1,1-trifluoroacetylacetone (Htfa) in the presence of Et3N afforded [Ln(LH) (tfa)2] [Ln = Dy3+ (1), Ln = Tb3+ (2), and Ln = Gd3+ (3)], while under the same reaction conditions, but in the absence of the coligand, another series of mononuclear complexes, namely, [Ln(LH)2]·Cl·2MeOH] [Ln = Dy3+ (4) and Tb3+ (5)] are obtained. Single-crystal X-ray diffraction analysis revealed that the former set contains a mono-deprotonated [LH]- and two tfa ligands, while the latter set comprises of two mono-deprotonated [LH]- ligands that are nearly perpendicular to each other at an angle of 86.9°. Among these complexes, 2 exhibited a ligand-sensitized lanthanide-characteristic emission. Analyses of the alternating current susceptibility measurements reveal the presence of single-molecule magnet behavior for 1 and 4, in the presence of direct-current field, with effective energy barriers of 4.6 and 44.4 K, respectively. The enhancement of the effective energy barrier of the latter can be attributed to the presence of a large energy gap between the ground and first excited Kramers doublets, triggered by the change in coordination environments around the lanthanide centers.

Pentagonal-Bipyramid Ln(III) Complexes Exhibiting Single-Ion-Magnet Behavior: A Rational Synthetic Approach for a Rigid Equatorial Plane

A pentadentate chelating ligand is employed for the facile synthesis of air-stable pentagonal-bipyramid Ln(III) complexes with a rigid equatorial plane. The Dy(III) analogue exhibits single-ion-magnet behavior with Ueff/ kB = 70 K under Hdc = 500 Oe.

Stepwise Reversible Oxidation of N-Peralkyl-Substituted NHC–CAAC Derived Triazaalkenes: Isolation of Radical Cations and Dications

Herein, the isolation and characterization of N-peralkyl-substituted NHC-CAAC derived triazaalkenes in three oxidation states, neutral, radical cation, and dication, are reported. Cyclic voltammetry has shown the reversible electronic coupling between the first and second oxidation to be ΔE1/2 = 0.50 V. As a proof-of-principle, to demonstrate the electron-rich nature of the triazaalkene, it was shown that it can be used as an electron donor in the reduction of an aryldiazonium salt to the corresponding arene.

Heterometallic Octanuclear NiII4LnIII4 (Ln = Y, Gd, Tb, Dy, Ho, Er) Complexes Containing NiII2LnIII2O4 Distorted Cubane Motifs: Synthesis, Structure, and Magnetic Properties

The reaction of 2-methoxy-6-[{2-(2-hydroxyethylamino)ethylimino}methyl] phenol (LH3) with lanthanide metal salts followed by the addition of nickel acetate allowed isolation of a family of octanuclear complexes, [Ni4Ln4(μ2-OH)2(μ3-OH)4(μ-OOCCH3)8(LH2)4]·(OH)2·xH2O. Single crystal X-ray diffraction studies of these complexes reveal that their central metallic core consists of two tetranuclear [Ni2Ln2O4] cubane subunits fused together by acetate and hydroxide bridges. The magnetic study of these complexes reveals a ferromagnetic interaction between the LnIII and the NiII center. The magnitude of exchange coupling between the NiII and LnIII center, parametrized from the magnetic data of the Gd analogue, gives J = +0.86 cm–1. The magneto caloric effect, studied for the NiII4GdIII4 complex, shows a maximum of magnetic entropy change, −ΔSm = 22.58 J kg–1 K–1 at 3 K for an applied external field of 5 T.

CCDC 1509723: Experimental Crystal Structure Determination

Related Article: Debabrata Dhara, Debdeep Mandal, Avijit Maiti, Cem B. Yildiz, Pankaj Kalita, Nicolas Chrysochos, Carola Schulzke, Vadapalli Chandrasekhar, Anukul Jana||Dalton Trans.|||doi:10.1039/C6DT04321F

CCDC 1509722: Experimental Crystal Structure Determination

Related Article: Debabrata Dhara, Debdeep Mandal, Avijit Maiti, Cem B. Yildiz, Pankaj Kalita, Nicolas Chrysochos, Carola Schulzke, Vadapalli Chandrasekhar, Anukul Jana||Dalton Trans.|||doi:10.1039/C6DT04321F