Amit Adhikary

Two Isostructural 3D Lanthanide Coordination Networks (Ln = Gd3+, Dy3+) with Squashed Cuboid-Type Nanoscopic Cages Showing Significant Cryogenic Magnetic Refrigeration and Slow Magnetic Relaxation

Two isostructural lanthanide-based 3D coordination networks [Ln = Gd(3+) (1), Dy(3+)(2)] with densely packed distorted cuboid nanoscopic cages are reported for the first time. Magnetic characterization reveals that complex 1 shows a significant cryogenic magnetocaloric effect (-ΔSm = 44 J kg(-1) K(-1)), whereas 2 shows slow relaxation of magnetization.

High Nuclearity (Octa-, Dodeca-, and Pentadecanuclear) Metal (M = CoII, NiII) Phosphonate Cages: Synthesis, Structure, and Magnetic Behavior

The synthesis, structural characterization, and magnetic property studies of five new transition metal (M = Co, Ni) phosphonate-based cages are reported. Three substituted phenyl and benzyl phosphonate ligands [RPO3H2; R1 = p-tert-butylbenzyl, R2 = p-tert-butylphenyl, R3 = 3-chlorobenzyl] were synthesized and employed to seek out high-nuclearity cages. Complexes 1-3 are quasi-isostructural and feature a dodecanuclear metal-oxo core having the general molecular formula of [M12(μ3-OH)4 (O3PR)4(O2C(t)Bu)6 (HO2C(t)Bu)6(HCO3)6] {M = Co, Ni and R = R1 for 1 (Co12), R2 for 2, 3 (Co12, Ni12)}. The twelve metal centers are arranged at the vertices of a truncated tetrahedron in a manner similar to Keggin ion. Complex 4 is an octanuclear nickel phosphonate cage [Ni8(μ3-OH)4 (OMe)2(O3PR1)2 (O2C(t)Bu)6(HO2C(t)Bu)8], and complex 5 represents a pentadecanuclear cobalt phosphonate cage, [Co15(chp)8(chpH) (O3PR3)8(O2C(t)Bu)6], where chpH = 6-chloro-2-hydroxypyridine. Structural investigation reveals some interesting geometrical features in the molecular cores, which may provide new models in single molecular magnetic materials. Magnetic property measurements of compounds 1-5 indicate the coexistence of both antiferromagnetic and ferromagnetic interactions between magnetic centers for all cages.

A 3D Iron(II)-Based MOF with Squashed Cuboctahedral Nanoscopic Cages Showing Spin-Canted Long-Range Antiferromagnetic Ordering

The reaction of dilithium squarate with Fe(II) perchlorate led to the formation of a new Fe(II)-based 3D MOF, [Fe3(OH)3(C4O4)(C4O4)0.5]n (1), with homoleptic squashed cuboctahedral cages. Complex 1 crystallizes in the monoclinic C2/c space group. Fe(II) centers in the complex are octahedrally coordinated by four squarate dianions in axial and equatorial positions and two hydroxyl groups in the remaining equatorial positions. The interesting structural feature of 1 is that the three-dimensional framework is an infinite extension of nanoscopic cuboctahedral cages. The framework also contains two types of voids; the larger hydrophobic ones are surrounded by aromatic squarate ligands, while the smaller ones are hydrophilic with hydroxyl groups on the surface connected by bifurcated hydrogen bonding interaction. A variable temperature magnetic study shows spin-canted long-range antiferromagnetic ordering in the low temperature regime.

Magnetic refrigeration and slow magnetic relaxation in tetranuclear lanthanide cages (Ln = Gd, Dy) with in situ ligand transformation

Three new Ln3+ coordination compounds having formulae, [Gd4(μ3-OH)2(L)2L1L2(HOCH3)2]·11H2O (1), [Dy4(μ3-OH)2(L)2L1L2(H2O)2]·11H2O (2) and [Dy4(μ4-O)(OMe)(HOMe)2(CH3COO)3(L3)2]·2H2O (3), have been synthesized in a one pot synthesis from O-vanillin, diaminomaleonitrile (DAMN), LnCl3·6H2O (Ln = Gd3+, Dy3+) and sodium acetate for 3, {H2L = 2,3-bis((E)-(2-hydroxy-3-methoxy benzylidene) amino)maleonitrile, HL1 = (2-amino-3-((E)-(2-hydroxy-3-methoxy benzylidene)amino)maleonitrile), H3L2 = ((1E,3Z,8Z,10E)-1,6,11-tris(2-hydroxy-3-methoxyphenyl)-2,5,7,10-tetraazaundeca-1,3,8,10-tetraene-3,4,8,9-tetracarbonitrile) and H2L3 = 2-((cyano(2-hydroxy-3-methoxyphenyl)methyl)amino)-3-((E)-(2-hydroxy-3-methoxybenzylidene)amino)maleonitrile. Single-crystal X-ray diffraction studies reveal that compounds 1 and 2 are quasi-isostructural, exhibiting tetranuclear hemicubane-like cores. For 3 the metal centers are arranged in a tetrahedral arrangement. Complexes 1–3 were formed with the ligands (L1–L3), which resulted in situ during synthesis. Magnetic studies reveal that compound 1 shows significant magnetocaloric effect (ΔSm = −27.2 J kg−1 K−1) at 3 K and 7 T. The magnetic properties of 2 and 3 are considerably different. Indeed, no out-of-phase alternating current (ac) signal is noticed for 2, whereas 3 shows a slow relaxation of magnetization. These differences are most likely due to the different Dy–O–Dy angles observed for the respective cores.

An unprecedented octadecanuclear copper(II) pyrazolate-phosphonate nanocage: synthetic, structural, magnetic, and mechanistic study.

A novel octadecanuclear copper pyrazolate-phosphonate nanocage with a bowl-shaped arrangement of the copper(II) centers in the asymmetric unit is reported. Characterization of intermediates in both solid and solution states aids to propose the mechanism of such a giant aggregation. Magnetic studies affirm the presence of antiferromagnetic interactions between the adjacent copper(II) centers. Extensive supramolecular interactions result in a framework structure.

Correction to Serendipitous Assemblies of Two Large Phosphonate Cages: A Co15 Distorted Molecular Cube and a Co12 Butterfly Type Core Structure

This report describes the synthesis, characterization, and magnetic properties of two novel phosphonate-based Co(II) cages. Structural investigation reveals some interesting geometrical features in the molecular core that may provide new models in single molecular magnetic materials.

Synthesis, crystal structure, magnetic study and magneto-structural correlation of three Cu(II) complexes formed via pyridine bis(hydrazone) based ligand

This report describes the synthesis and characterization of three different complexes of molecular formulae {[Cu6L2(ClO4)4(μ-ClO4)2(H2O)9](ClO4)2·8H2O}n(1), [Cu6L2Cl6(μ2-Cl)2(H2O)2]·3H2O (2) and [Cu9L6](ClO4)6·6H2O·2CH3CN·CH3OH (3), where, H2L = bis[(2-pyridyl)methylene] pyridine 2,6 dicarbohydrazone. X-ray crystallography reveals that complex 1 exhibits 1D chain, complex 2 is a hexanuclear entity and an unsymmetrical [3 × 3] grid formation in complex 3. Variable temperature magnetic measurements were performed, they show that weak antiferromagnetic interactions exist among the metal centers in complex 1 and both ferro- and antiferromagnetic interactions coexist for complexes 2 and 3. Below 20 K antiferromagnetic interactions dominate for complex 2 whereas it is ferromagnetic for complex 3. Transformation from one cage to another is possible at mild reaction conditions, which results in a dramatic change in the magnetic properties.

Magnetically Frustrated Quaternary Chalcogenides with Interpenetrating Diamond Lattices

A series of quaternary sulfides of the composition Na3MGaS4 (M = Mn (1), Fe (2), and Co (3)) have been synthesized in sealed quartz ampules. In these compounds, divalent transition metal and Ga occupy the same crystallographic site in the Ga-S network, forming a supertetrahedral, T2 (adamantane) unit, through the corner-sharing of four M/GaS4 tetrahedra. The corner sulfur atoms of the T2 clusters are further connected to similar T2 units to form an open continuous three-dimensional (3D) anionic framework of composition {[Ga2M2S8]n}6-. The framework resembles a zinc blende structure type if each T2 cluster is considered as a single tetrahedron and two such frameworks are intertwined to generate channels wherein reside the extra-framework Na+ ions. Placement of transition metals (Mn or Fe or Co) in the corner of a perfect supertetrahedron, adamantane building unit, generates an ideal lattice for geometrical magnetic frustration, which, on dilution with nonmagnetic metal (Ga), creates an ideal case for random frustration. Preliminary magnetic measurements indicate high negative values of the Weiss constant (-200 to -400 K) and the absence of any magnetic ordering, reinforcing the presence of magnetic frustration in all of these compounds.

Metallic Ternary Telluride with Sphalerite Superstructure

A new ternary compound with composition Cu5Sn2Te7 has been synthesized using the stoichiometric reaction of Cu, Sn, and Te. The compound crystallizes in C2 space group with unit cell parameters of a = 13.549(2) Å, b = 6.0521(11) Å, c = 9.568(2) Å, and β = 98.121(2)°. Cu5Sn2Te7 is a superstructure of sphalerite and exhibits tetrahedral coordination of Cu, Sn, and Te atoms, containing a unique adamantane-like arrangement. The compound is formally mixed valent with a high electrical conductivity of 9.8 × 10(5) S m(-1) at 300 K and exhibits metallic behavior having p-type charge carriers as indicated from the positive Seebeck coefficient. Hall effect measurements further confirm holes as charge carriers with a carrier density of 1.39 × 10(21) cm(-3) and Hall mobility of 4.5 cm(2) V(-1) s(-1) at 300 K. The electronic band structure calculations indicate the presence of a finite density of states around the Fermi level and agree well with the p-type metallic conductivity. Band structure analysis suggests that the effective mass of the hole state is small and could be responsible for high electronic conductivity and Hall mobility. The high thermal conductivity of 15.1 W m(-1) K(-1) at 300 K coupled with the low Seebeck coefficient results in a poor thermoelectric figure of merit (ZT) for this compound. Theoretical calculations indicate that if Cu5Sn2Te7 is turned into a valence precise compound by substituting one Cu by a Zn, a semiconducting material, Cu4ZnSn2Te7, with a direct band gap of ∼ 0.5 eV can be obtained.