Debajyoti Ghoshal

Synthesis, crystal structure and magnetic behavior of three polynuclear complexes: [Co(pyo)2(dca)2]n, [Co3(ac)4(bpe)3(dca)2]n and [{Co(male)(H2O)2}(H2O)]n [pyo, pyridine-N-oxide; dca, dicyanamide; ac, acetate; bpe, 1,2-bis-(4-pyridyl)ethane and male, maleate]

Three polymeric cobalt(II) complexes of formulae [Co(pyo)2(dca)2]n (1), [Co3(ac)4(bpe)3 (dca)2]n (2) and [{Co(male)(H2O)2(H2O)]n (3) [pyo, pyridine-N-oxide; dca, dicyanamide; ac, acetate; bpe, 1,2-bis-(4-pyridyl)ethane and male, maleate] have been synthesized and characterized structurally as well as magnetically. The structure determination of complex 1 shows that each octahedral Co(II) in the 1D coordination chain is attached with four μ-1,5-dicyanamide and two pendant pyridine-N-oxide ligands, which form mutual relationships with other 1D chains through non-covalent π-π interactions, giving rise to a 2D infinite sheet-like structure. The molecular structure reveals that complex 2 adopts an infinite three-leg ladder-like structure in which three parallel 1D Co(bpe) chains are connected by syn-syn and oxo bridging acetate ligands. The dicyanamide ligands are pendant to the terminal Co(II) centers. Complex 3 is an infinite 3D network in which carboxylate groups of the maleate ligand are linked to Co(II) centers in syn-anti fashion. The structure of complex 3 has already been reported. The variable temperature (300–2 K) magnetic measurements have been performed for all three complexes. In the case of 2, the full structure can be rationalized as quasi-isolated trimers; the exchange Hamiltonian that describes magnetic interactions between the effective S′ = 1/2 spins, at low temperature is . Fixing g⊥ = 6.01 and g∣∣ = 2.25, according to the EPR measurements at 4 K, 2J = −3.3 cm−1 is the best-fit parameter. For 1 and 3, complete fits are not possible for calculating the corresponding J parameters for the one- and three-dimensional structures, respectively. Only an approximate J value has been calculated for 1.

Polymeric networks of copper(II) using succinate and aromatic N–N donor ligands: synthesis, crystal structure, magnetic behaviour and the effect of weak interactions on their crystal packing

Four succinato-bridged complexes of copper(II) have been synthesized. Complex 1, [Cu(2)(mu-OH(2))(2)L(bpy)(2)(NO(3))(2)](n) and 2, [Cu(2)(mu-OH(2))(2)L(phen)(2)(NO(3))(2)](n)(bpy = 2,2[prime or minute]-bipyridine; phen = 1,10-phenanthroline and LH(2)= succinic acid) exhibit 1D coordination polymer structures where both the nitrate ions are directly linked to the copper(ii) producing synthons in a 2D sheet. A novel 2D grid-like network, ([Cu(4)L(2)(bpy)(4)(H(2)O)(2)](ClO(4))(4)(H(2)O))n3, is obtained upon changing the nitrate by perchlorate anion in complex 1, where the channels are occupied by the anions. On changing the nitrate by tetrafluoroborate anion in complex 2, a novel octanuclear complex, [Cu(8)L(4)(phen)(12)](BF(4))(8).8H(2)O 4, is isolated. The coligand bpy and phen in these complexes show face-to-face (in 1,2,3,4) or edge-to-face (in 4 )pi-pi interactions forming the multidimensional supramolecular architectures. Interestingly, the appearance of edge-to-face pi-pi interactions in complex facilitates the formation of discrete octanuclear entities. Variable-temperature (300-2 K) magnetic measurements of complexes have been done. Complexes 1 and 2 show very weak antiferromagnetic (OOC-CH(2)-CH(2)-COO) and ferromagnetic coupling (mu-H(2)O). Complex 3 also shows antiferromagnetic (syn-syn mu-OCO), and ferromagnetic coupling (mu-O of the -COO group). Complex 4 with two types (syn-syn and syn-anti) of binding modes of the carboxylate group shows strong antiferromagnetic interaction.

Cd(II) based metal–organic framework behaving as a Schottky barrier diode

A metal-organic framework (MOF) of cadmium(ii) is reported here which is the first example of an experimentally achieved MOF based electronic device, and in the present case it is a Schottky diode.

A novel 2D mixed valence copper(I/II) rectangular grid constructed with pyrazine and croconate

A novel 2D rectangular grid coordination polymer with a mixed valence localized copper(I/II), [Cu2ICuII(pyz)2(C5O5)2 (H2O)2]n (pyz, pyrazine; C5O52−, croconate dianion) has been hydrothermally synthesized viain situ redox reaction of Cu(II), and characterized by X-ray diffraction analysis, magnetic and EPR study. The structure extends to a 3D supramolecular network through H-bonding.

Structural diversity in manganese squarate frameworks using N,N-donor chelating/bridging ligands: syntheses, crystal structures and magnetic properties

Three new polymeric squarato-bridged manganese complexes {[Mn(H(2)O)(2)(bpe)(sq)].bpe.H(2)O}(n) (1), [Mn(2)(H(2)O)(4)(phen)(2)(sq)(2)](n) (2) and [Mn(2)(H(2)O)(2)(phen)(4)(sq)].(sq).8(H(2)O) (3) [bpe, 1,2-bis(4-pyridyl)ethane; phen, 1,10-phenanthroline; sq, squarate dianion] have been synthesized and characterized by single crystal X-ray diffraction analysis and variable temperature magnetic studies. Complex 1 is a 2D rectangular grid-like structure, achieved through flexible bpe bridging ligands and squarate dianions. On the other hand the use of chelating phen instead of bpe gives rise to a 1D polymeric chain in complex 2 and to a dinuclear entity in 3. In all the three complexes weak interactions play a vital role in stabilizing the solid-state structure. Variable temperature (2-300 K) magnetic studies indicate weak antiferromagnetic coupling between the metal centres in all the complexes.

Selective carbon dioxide adsorption by mixed-ligand porous coordination polymers

Porous coordination polymers (PCPs), also referred to as metal–organic frameworks (MOFs), have firmly established themselves as a class of excellent solid-state sorbents for carbon dioxide (CO2) along with their other several exciting properties. The mixed-ligand PCPs, constructed with polycarboxylates and N,N′-donor ligands, have been adopted for the fabrication of novel functional PCPs/MOFs, as the combination of different ligands with metal ions offer a better control over the structural variation of the frameworks compared to a single ligand. In this highlight, we have emphasized some of such important mixed linker-based MOFs with different carboxylate ligands and N,N′-donor linkers that act as excellent materials for CO2 adsorption and separation. The prospect of such mixed-ligand MOFs for the effective separation and sequestration of CO2 is also addressed by means of discussing different strategies for designing mixed-ligand MOFs that not only can potentially improve the amount of CO2 adsorption but also can increase the selectivity of CO2 uptake over other gases and volatiles.

Five diverse bivalent metal coordination polymers based on benzene dicarboxylate and bent dipyridyl ligands: syntheses, structures, and photoluminescent properties

Five new mixed ligand coordination polymers, {[Co0.5(H2O)(1,4-bdc)(3-bpdb)Co0.5(H2O)2]·(H2O)3}n (1), [Co(3-bpdh)(1,4-bdc)(H2O)2]n (2), [Zn(3-bpdb)(1,4-bdc)]n (3), {[Zn(3-bpdh)(1,4-bdc)]·(3-bpdh)0.5}n (4) and [Cd(3-bpdb)(1,4-bdc)(H2O)]n (5) [where 3-bpdb = 1,4-bis-(3-pyridyl)-2,3-diaza-1,3-butadiene; 3-bpdh = 2,5-bis-(3-pyridyl)-3,4-diaza-2,4-hexadiene and 1,4-bdc = benzene-1,4-dicarboxylate] were synthesized at room temperature. The structures of 1–5 were determined by single crystal X-ray diffraction analysis and were further characterized by elemental analysis, infrared spectroscopy (IR) and powder X-ray diffraction (PXRD). Compound 1 exhibits a one-dimensional (1D) chain structure with monodentate pendant 1,4-bdc ligands which further extend to a three-dimensional (3D) supramolecular structure by H-bonding and π⋯π interactions. Compound 2 displays a 4-connected two-dimensional (2D) framework with the point symbol {44·62}. Moreover, the 2D structure of 2 is also ultimately packed into 3D supramolecular frameworks through H-bonding and π–π stacking interactions. Compound 3 shows a 5-fold interpenetrated diamondoid net with 66 topology. Compound 4 is a 2D 3-connected net having a point symbol {63} and is extended to a supramolecular 3D structure through C–H⋯π and π⋯π interactions with lattice 3-bpdh ligands. Compound 5 features a 3-fold interpenetrated diamondoid net with 66 topology. The thermal stabilities and luminescent properties of 3–5 were also studied in detail. The complexes exhibit ligands based photoluminescence properties at room temperature.

Towards rational design of supramolecular helices using linear pseudohalides in Cd(II) - 2,2′-biimidazole system

Three cadmium complexes, [Cd(H2biim)2(SCN)2] (1), [Cd(H2biim)2(SeCN)2] (2) and [Cd(H2biim)2(dca)2] (3) [H2biim = 2,2′-biimidazole; dca = dicyanamide] have been synthesized and characterized by X-ray single crystal structure analysis. In complexes 1 and 2 monomeric units assemble into supramolecular helix whereas in 3 monomeric units assemble into supramolecular 2-D grid with (4,4) net topology. The appearance of helical topology in complexes 1 and 2 is due to the linear nature of SCN−/SeCN− whereas (4,4) net topology in complex 3 is due to the bent nature of dca−. In each case R12(7) hydrogen bonding synthon is attained facilitating the helical and (4,4) net topology.

Synthesis, crystal structure and magnetic behavior of a croconato bridged Cu(II) complex: effect of C–H⋯O interaction in controlling the coordination bond formation in organic–inorganic hybrid

A 2-D croconato bridged complex of Cu(II), [{Cu(C5O5)(bpee)}·0.5H2O]n (1) [bpee, trans-1,2-bis(4-pyridyl)ethylene] has been synthesized by in situ hydrothermal reaction and characterized by X-ray diffraction analysis, variable temperature magnetic susceptibility measurement and EPR study. The structure determination reveals that the adjacent 2-D sheets are extended to 3-D supramolecular architecture through π–π and trifurcated C–H⋯O interactions, which inhibit the oxygen atom of croconate from forming the usual bridging mode.

Flexible dicarboxylate based pillar-layer metal organic frameworks: differences in structure and porosity by tuning the pyridyl based N,N′ linkers

Dicarboxylate supported metal organic hybrids of Co(II), Zn(II) and Cd(II) have been synthesized using two different pyridyl based N,N′ linkers having Schiff base functionalized site. The use of flexible dicarboxylate glutarate in designing such frameworks has created a marked diversity in topology. The different N,N′ donor linkers also played an active part in the channel modification in the synthesized MOFs. The structural and topological diversity has been analyzed from the single crystal X-ray structure. Five compounds, {[Co(azpy)(glut)]·(CH3OH)}n (1), {[Co(meazpy)(glut)(H2O)2]·(H2O)3}n (2), {[Zn(azpy)0.5(glut)(H2O)]·(azpy)0.5}n (3), {[Zn(meazpy)0.5(glut)(H2O)]·(H2O)2}n (4) and {[Cd(azpy)(glut)]·(CH3OH)}n (5), show porous structures with solvent accessible voids. The nature of the pores as well as the existence of lattice solvent molecules in 1 and 2 are different due to the use of a different pillar ligand in their fabrication. In case of 3 and 4 there are some nice effects of non-covalent interaction in the construction of their solid state structure, which has also originated by the change of pillar N,N′ donor linkers. Complex 5 is topologically as well as structurally similar to 1 forming a 2D-grid like structure. In {[Cd2(meazpy)2(glut)(NO3)]2}n (6) there is a formation of 2D sheets with the coordinated counter anion. Interestingly, here the sheets are disposed in a perpendicular fashion to each other and do not contain any solvent accessible void. Upon removal of the solvent molecules, the frameworks 1–5 show moderate CO2 and H2 uptake at 273 K and 77 K, respectively. The desolvated frameworks show different quantities of CO2 and H2 uptake which has been corroborated to their structures.