Sanjit Nayak

Magnetothermal Studies of a Series of Coordination Clusters Built from Ferromagnetically Coupled {MnII4MnIII6} Supertetrahedral Units

Three high-nuclearity mixed valence manganese(II/III) coordination clusters, have been synthesised, that is, [Mn(III) (6)Mn(II) (4)(μ(3)-O)(4)(HL(1))(6)(μ(3)-N(3))(3)(μ(3)-Br)(Br)](N(3))(0.7)/(Br)(0.3)⋅3 MeCN⋅2 MeOH (1) (H(3)L(1)=3-methylpentan-1,3,5-triol), [Mn(III) (11)Mn(II) (6)(μ(4)-O)(8)(μ(3)-Cl)(4)(μ,μ(3)-O(2)CMe)(2)(μ,μ-L(2))(10)Cl(2.34)(O(2)CMe)(0.66)(py)(3)(MeCN)(2)]⋅7 MeCN (2) (H(2)L(2)=2,2-dimethyl-1,3-propanediol and py is pyridine), and [Mn(III) (12)Mn(II) (7)(μ(4)-O)(8)(μ(3)-η(1)N(3))(8)(HL(3))(12)(MeCN)(6)]Cl(2)⋅10 MeOH ⋅MeCN (3) (H(3)L(3)=2,6-bis(hydroxymethyl)-4-methylphenol) with high ground-spin states, S=22, 28±1, and 83/2, respectively; their magnetothermal properties have been studied. The three compounds are based on a common supertetrahedral building block as seen in the Mn(10) cluster. This fundamental magnetic unit is made up of a tetrahedron of Mn(II) ions with six Mn(III) ions placed midway along each edge giving an inscribed octahedron. Thus, the fundamental building unit as represented by compound 1 can be described as a Mn(10) supertetrahedron. Compounds 2 and 3 correspond to two such units joined by a common edge or vertex, respectively, resulting in Mn(17) and Mn(19) coordination clusters. Magnetothermal studies reveal that all three compounds show interesting long-range magnetic ordering at low temperature, originating from negligible magnetic anisotropy of the compounds; compound 2 shows the largest magnetocaloric effect among the three compounds. This is as expected and can be attributed to the presence of a small magnetic anisotropy, and low-lying excited states in compound 2.

Chemical and Structural Stability of Zirconium‐based Metal–Organic Frameworks with Large Three‐Dimensional Pores by Linker Engineering

The synthesis of metal–organic frameworks with large three-dimensional channels that are permanently porous and chemically stable offers new opportunities in areas such as catalysis and separation. Two linkers (L1=4,4′,4′′,4′′′-([1,1′-biphenyl]-3,3′,5,5′-tetrayltetrakis(ethyne-2,1-diyl)) tetrabenzoic acid, L2=4,4′,4′′,4′′′-(pyrene-1,3,6,8-tetrayltetrakis(ethyne-2,1-diyl))tetrabenzoic acid) were used that have equivalent connectivity and dimensions but quite distinct torsional flexibility. With these, a solid solution material, [Zr6O4(OH)4(L1)2.6(L2)0.4]⋅(solvent)x, was formed that has three-dimensional crystalline permanent porosity with a surface area of over 4000 m2 g−1 that persists after immersion in water. These properties are not accessible for the isostructural phases made from the separate single linkers.

An S-Shaped [Fe4Dy2] Complex Exhibiting Slow Relaxation of Magnetization: Synthesis, Magnetism, and Crystal Structures of a Family of [Fe4Ln2][Ln] Coordination Compounds (Ln = Nd, Gd, Tb, Dy, and Ho)

A series of heterobimetallic 3d-4f cluster coordination compounds has been synthesized using a Schiff-base ligand (H(3)L), a trinuclear iron(III) precursor complex and lanthanide nitrates as reactants. Five new isostructural complexes were prepared with the ligand in 4 different forms, i.e., neutral and 3 different levels of deprotonation, and with the general formula [Fe(III)(4)Ln(III)(2)(H(2)L)(2)(HL)(2)L(2)(CH(3)OH)(2)((CH(3))(3)CCOO)(2)(NO(3))(2)][Ln(III)(NO(3))(4)(H(3)L)(CH(3)OH)].NO(3).H(2)O, where Ln is Nd, Gd, Tb, Dy, and Ho for compounds 1, 2, 3, 4, and 5, respectively. The single-crystal structures of two complexes were determined by X-ray diffraction, consisting of an original [Fe(III)(4)Ln(III)(2)](2+) moiety with a linear S-shaped [Ln-Fe(4)-Ln] core and an isolated Ln(III) ion coordinated by nitrate anions and the neutral Schiff-base ligand. The isostructural nature of all five coordination compounds is further illustrated both by XRPD and IR analysis. Magnetic properties of all five compounds have been studied and are discussed in light of magnetostructural considerations. Among these five compounds, the Dy (4) cluster shows frequency-dependent ac-susceptibility indicative of probable single-molecule magnet behavior.

New Three-Dimensional Metal−Organic Framework with Heterometallic [Fe−Ag] Building Units: Synthesis, Crystal Structure, and Functional Studies

A new three-dimensional metal-organic framework (MOF) containing Fe(II) and Ag(I) ions and 2-pyrazinecarboxylic acid (pcaH) was synthesized, and its magnetic and catalytic properties were studied. The MOF has a big window size of 12.1 × 12.0 Å, with 23.8% solvent-accessible space, and shows size selectivity toward Lewis acid catalysis.

Discrete Tetrairon(III) Cluster Exhibiting a Square-Planar Fe4(μ4-O) Core: Structural and Magnetic Properties

The aerobic reaction of the Schiff-base ligand N-(benzimidazol-2-yl)salicylaldimine (Hbisi) with iron(II) perchlorate in methanol leads to the formation of the remarkable coordination compound [Fe(4)(mu(4)-O)(mu-MeO)(4)(bisi)(4)](ClO(4))(2) x 4 MeOH (1), whose single-crystal X-ray structure reveals the presence of a discrete Fe(III)(4)(mu(4)-O) core. Magnetic and Mossbauer studies both show that the exchange interaction within the square tetranuclear iron(III) unit is dominated by the central bridging mu(4)-oxido ligand, the involvement of the mu-methoxido bridges being negligible.

Hydrogen bond assisted co-crystallization of a bimetallic MnIII2NiII2 cluster and a NiII2 cluster unit: synthesis, structure, spectroscopy and magnetism

A new bimetallic Schiff-base composite complex [Ni₂(LH₂)₂(H₂O)₂Cl₂][Mn₂Ni₂(LH)₄]₂Cl₄(CH₃OH) (1) has been synthesized by a simple one-pot reaction. The compound was structurally characterized by single-crystal X-ray diffraction. In the crystal structure the dinuclear nickel units are connected to the tetranuclear Mn₂Ni₂ units by means of strong hydrogen-bonding interactions. The compound was further characterized by ESI-MS, ligand-field and infrared spectroscopy. The magnetic properties of the compound have been studied in combination with preliminary DFT calculations, and have resulted in the successful determination of the nature of the magnetic exchange interactions between the metal ions, and hence the coupling constants.

Polynuclear Complexes as Precursor Templates for Hierarchical Microporous Graphitic Carbon: An Unusual Approach

A highly porous carbon was synthesized using a coordination complex as an unusual precursor. During controlled pyrolysis, a trinuclear copper complex, [CuII3Cl4(H2L)2]·CH3OH, undergoes phase changes with melt and expulsion of different gases to produce a unique morphology of copper-doped carbon which, upon acid treatment, produces highly porous graphitic carbon with a surface area of 857 m2 g-1 and a gravimetric hydrogen uptake of 1.1 wt % at 0.5 bar pressure at 77 K.