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To overcome the environmental issues arising from the burning of fossil fuel, an alternative effective source of energy is required. Hydrogen energy is one such alternative which can pave the purpose of interest. For a successive replacement of fossil fuel by hydrogen energy, hydrogen storing, especially in a vehicular system, is highly required and it is still a major challenge. A wide range of materials have been used for hydrogen storing. Metal-organic framework is one of them, which have been studied extensively both from academic and industrial viewpoint. These studies show that several metal-organic frameworks (MOFs) have excellent physisorption ability but normally at a very low temperature. To improve this at ambient conditions, various strategies have been introduced so far for MOFs, although an important aspect of external stimuli-responsive flexible or dynamic frameworks, have not been studied systematically. There are various advantages of the use of dynamic MOFs for hydrogen physisorption and sometimes helpful to overcome socio-economical barrier connected to this alternative energy source. In this highlight, prior strategies to improve hydrogen storage in MOF with special importance on external stimuli-responsive flexible MOF and their perspective importance in hydrogen storage have been discussed.

Highly symmetric enneanuclear copper(II) phosphates [Cu9(Pz)6(μ-OH)3(μ3-OH)(ArOPO3)4(DMF)3] (PzH = pyrazole, Ar = 2,6-(CHPh2)2-4-R-C6H2; R = Me, 2MeAr; Et, 2EtAr; iPr, 2iPrAr; and Ar = 2,6-iPr2C6H3, 2Dip) comprising nine copper(II) centers and pyrazole, hydroxide and DMF as ancillary ligands were synthesized by a reaction involving the arylphosphate monoester, 1, copper(I)chloride, pyrazole, and triethylamine in a 4 : 9 : 6 : 14 ratio. All four complexes were characterized by single crystal structural analysis. The complexes contain two distinct structural motifs within the multinuclear copper scaffold: a hexanuclear unit and a trinuclear unit. In the latter, the three Cu(II) centres are bridged by a μ3-OH. Each pair of Cu(II) centers in the trinuclear unit are bridged by a pyrazole ligand. The hexanuclear unit is made up of three dinuclear Cu(II) motifs where the two Cu(II) centres are bridged by an –OH and a pyrazole ligand. The three dinuclear units are connected to each other by phosphate ligands. The latter also aid the fusion of the trinuclear and the hexanuclear motifs. Magnetic studies reveal a strong antiferromagnetic exchange between the Cu(II) centres of the dinuclear units in the hexanuclear part and a strong spin frustration in the trinuclear part leading to a degenerate ground state.

A novel benzimidazole appended arylimide (pyromellitic, naphthalene and perylene) based covalent organic framework (COF) has been synthesized through the condensation polymerization pathway, by taking consideration of the special noncovalent interaction with carbon dioxide. Formation and chemical connectivities of these polymers were thoroughly investigated by 13 C NMR and FTIR studies. Presences of pores in these polymers have been primarily checked with FESEM and HRTEM observations, prior to adsorption studies. The pyromellitic diimide containing benzimidazole COF (BIBDZ) exhibit highest BET surface area, 177.095 m 2 g −1 with pore diameter of 30–32 angstorm among the COFs reported here which is also consistent with our computational study. Naphthalene diimide and the diaminobenzidine containing COF (NIBDZ) has the highest binding affinity with CO 2 i.e. 127.87 cc g −1 (14.56 wt%) at 195 K, than the other two COFs. On the other side BIBDZ has showed specific capacitance value of 88.4 F g −1 at 0.5 A g −1 current density in the 1M H 3 PO 4 electrolytic solution as well as remarkable retention of specific capacitance (93.61%) after 5000 galvanostatic charge discharge cycles.

Because of their potential applications, coordination polymers (CPs) are at an exalted position in the field of chemical and material science. Porous coordination polymers, popularly known as metal–organic frameworks (MOFs), have large surface area with functional pore environment, permanent porosity, tailorability in pore size, dimension and volume, which make them promising for interesting functionalities. In this review, we show how the mixed-ligand CPs/MOFs are very important in tuning the functionality of such systems and how the X-ray structure illuminates their functionalities. Here, we discuss the application of mixed-ligand functional MOFs for CO2 storage and separation by fine-tuning their pore size and dimension along with their polar pore surfaces using different functional dicarboxylates and N,N′-donor ligands. We also discuss the nature of conductivity and fabrication of Schottky barrier diode for CPs, where free organic ligands are in their pores. In addition, we also present the variation of their interesting chemical reactivity, e.g. framework-assisted in situ redox transformation.

Assembly of diphenylphosphate (dpp) with Cu(II) salts in combination with the different N-donor linkers, e.g., pentamethyldiethylenetriamine (pmdeta), bis-(3-aminopropyl)amine (bapa) and 4-Picolene (4-pic), yielded three new metal-organic coordination complexes, namely {[Cu(dpp)(pmdeta)] ⋅ClO4.H2O}2 (1), {[{[Cu(dpp)(bapa)H2O] ⋅ClO4} (2) and [Cu(dpp)2(4-pic)2]2 (3) by stirring the constituent reactants at room temperature. Complexes 1–3 were characterized by single crystal X-ray diffraction analysis and were further characterized by elemental analysis, infrared spectroscopy (IR) and powder X-ray diffraction (PXRD) studies. Compound 1 exhibits a dimeric Cu(II) complex which forms a 1D supramolecular chain along the crystallographic c-axis by means of intermolecular π…π interactions. Compounds 2 and 3 form a monomeric and dimeric complex of Cu(II) respectively, which are further extended into a supramolecular 2D structure via C-H.. π interactions for 2 and a 3D structure for 3 with the help of both intermolecular C-H.. π and π…π interactions for 3. In addition, the solid state UV-Vis spectra of compounds 1-3 and free dpp ligand have been investigated at room temperature.

Single crystal X-ray diffraction of two macrocyclic bischalcones, namely, (2E,25E)-11,17,33,37-tetraoxapentacyclo[36.4.0.05,10.018,23.027,32]dotetraconta-1(42),2,5,7,9,18,20,22,25,27,29,31,38,40-tetradecaene-4,24-dione(1) and (2E,24E)-11,16,32,37-tetraoxapentacyclo[36.4.0.05,10.017,22.026,31]dotetraconta-1(42),2,5,7,9,17,19,21,24,26,28,30,38,40-tetradecaene-4,23-dione(2), each containing a 26-membered ring, has been studied. Compound 1 belongs to the monoclinic system, space group C2/c with a = 34.3615(9) Å, b = 12.7995(3) Å, c = 14.6231(3) Å, β = 96.912(2)°, V = 6,384.6(3) Å3, and Z = 8. Compound 2 is triclinic, space group P-1 with a = 10.066(2) Å, b = 10.670(3) Å, c = 16.590(3) Å, α = 85.95(2), β = 89.244(14), γ = 62.211(13), V = 1572.0(6) Å3, and Z = 2. Intermolecular C–H⋯O hydrogen bonding interactions are present in both compounds.

Figure. In two new complexes of Mn(II) and Zn(II), it has been observed that carboxylate (O)…π interactions played a crucial role in the organization of supramolecular structure and that carboxylate (O)…π interactions also somehow controlled by the C-H…π interactions, which is achieved by proper modulation of the linkers.

A solvothermal reaction of cadmium (II) nitrate with succinic acid and isonicotinic acid creates a novel 3D metal-organic framework, [Cd3(isonicotinate)2(suc)2]n(1). Single crystal X-ray structure determination reveals that complex 1 posses two crystallographically independent Cd(II) centres. The succinate anion acts here as a heptadented ligand and binds five Cd(II) centre simultaneously. The heptacoordinated Cd(II) centres are oxo-bridged by succinate moiety and the hexacoordinated metal centres are terminally connected through four different succinate moiety to make the overall 2D sheet arrangement. In unit cell, the ratio of hexadented Cd(II) and heptadented Cd(II) is 1:2. The new compound was also characterized by luminescence spectra and compared with the luminescence spectra of the pure isonicotinic acid.

Eight new metal-organic hybrid materials of Cu(ll) have been synthesized by using flexible glutarate/adipate as a bridging ligand, 2,2'-bipyridine/1,10-phenanthroline as a chelating ligand, and BF 4 -/Cl0 4 -/Cl- as a counteranion. These materials are characterized by single-crystal X-ray diffraction analyses and variable temperature magnetic measurements. Out of them, complexes 1, 3, 5, and 8 crystallize in the triclinic system with space group P1. Complexes 2, 4, 6, and 7 crystallize in the monoclinic system with space group P2 1 /n (2, 4), F2 1 /c (6), and C2 (7). The structural analysis reveals that bridging glutarate gives rise to dinuclear and tetranuclear species, whereas the adipate dianion leads to octanuclear, one-dimensional and two-dimensional polymeric complexes, although they have been prepared under similar conditions. Supramolecular architectures of higher dimensionality have been achieved through H-bonding and π-π interaction. In all the complexes, the bridging and/or counteranions as well as chelating ligand have a vital role in directing the solid-state structure. A variable temperature (2-300 K) magnetic susceptibility study discloses the antiferromagnetic coupling for all of the complexes.

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.

Three polymeric Mn(II) complexes, {[Mn(N3)2(bpds)2](bpds)}n (1), {[Mn(N3)2(bpp)3](H2O)}n (2) and [Mn(OCN)2(bpp)2]n (3) [bpds=4,4′-bipyridyl disulfide, bpp=1,3-bis(4-pyridyl)propane] have been synthesized and characterized by single crystal X-ray analysis. Complexes 1 and 2 are 1D coordination polymers, which are extended through weak interactions to 2D sheet in case of 1 and 3D in case of 2. Complex 2 exhibits twofold parallel interpenetrating nets through the formation of H-bonds created by lattice water molecules. The crystal structure of complex 3 shows twofold parallel interpenetrating layers based on a 4,4 topology. The variable temperature magnetic study exhibits weak antiferromagnetic interactions between the metal centers in all the complexes.

Two new dicyanamido-bridged polymeric complexes of manganese(II), [Mn(dca)2(pic)2]n 1 and [Mn(dca)2(biim)]n 2 (dca = dicyanamide, pic = 4-picoline, biim = 2,2‘-biimidazole), have been synthesized a...

Two new polymeric azido-bridged manganese complexes of formulas [Mn(N3)2 (bpee)]n (1) and {[Mn(N3)(dpyo)Cl(H2O)2](H2O)}n (2) [bpee, trans-1,2-bis(4-pyridyl)ethylene; dpyo, 4,4'-dipyridyl N,N'-dioxide] have been synthesized and characterized by single-crystal X-ray diffraction analysis and low-temperature magnetic study. Both the complexes 1 and 2 crystallize in the triclinic system, space group P1, with a = 8.877(3) A, b = 11.036(3) A, c = 11.584(4) A, alpha = 72.62(2) degrees, beta = 71.06(2) degrees, gamma = 87.98(3) degrees, and Z = 1 and a = 7.060(3) A, b = 10.345(3) A, c = 11.697(4) A, alpha = 106.86(2) degrees, beta = 113.33(2) degrees, gamma = 96.39(3) degrees, and Z = 2, respectively. Complex 1 exhibits a 2D structure of [-Mn(N3)2-]n chains, connected by bpee ligands, whose pyridine rings undergo pi-pi and C-H...pi interactions. This facilitates the rare arrangement of doubly bridged azide ligands with one end-on and two end-to-end (EO-EE-EE) sequence. Complex 2 is a neutral 1D polymer built up by [Mn(N3)(dpyo)Cl(H2O)2] units and lattice water molecules. The metals are connected by single EE azide ligands, which are arranged in a cis position to the Mn(II) center. The 1D zipped chains are linked by H-bonds involving lattice water molecules and show pi-pi stacking of dpyo pyridine rings to form a supramolecular 2D layered structure. The magnetic studies were performed in 2-300 K temperature range, and the data were fitted by considering an alternating chain of exchange interactions with S = 5/2 (considered as classical spin) with the spin Hamiltonians H = -Ji sigma(S(3i)S(3i+1) + S(3i+1)S(3i+2)) - J2 sigmaS(3i-1)S(3i) and H = -Ji sigmaS(2i)S(2i+1) - J2 sigmaS(2i+1)S(2i+2) for complexes 1 and 2, respectively. Complex 2 exhibits small antiferromagnetic coupling between the metal centers, whereas 1 exhibits a new case of topological ferromagnetism, which is very unusual.

The structure of the title compound, catena-poly[[di-micro-azido-kappa(4)N(1):N(1)-bis[[bis(3-aminopropyl)methylamine-kappa(3)N]copper(II)]]-micro-cyano-[dicyanonickel(II)]-micro-cyano], [Cu(2)(N(3))(2)(medpt)(2)[Ni(CN)(4)]](n) [medpt is bis(3-aminopropyl)methylamine, C(7)H(19)N(2)] or [Cu(2)Ni(CN)(4)(N(3))(2)(C(7)H(19)N(3))(2)](n), is a one-dimensional heterometallic covalent chain where Ni(CN)(4)(2-) functions as a molecular ion bridge. The Ni atom sits on the centre of inversion. The chain undergoes hydrogen-bonding interactions, forming a three-dimensional supramolecular network.

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.

Two new polynuclear complexes of Cu(II), [(μ-1,1,3-N3)2{Cu2(me2tn)2(N3)2}]n (1) (me2tn=2,2-dimethylpropane-1,3-diamine) and [Cu2(μ-C2O4)(μ-N3)(ipr2en)2]n(ClO4)n (2) (ipr2en=N,N′-di-isopropylethane-1,2-diamine) have been synthesized and structurally characterized by X-ray crystallography. The crystal structure of 1 displays a 2D network in which distorted octahedral copper(II) centers, chelated by a me2tn ligand and bound to a terminal azide, are connected through μ-1,1,3 bridging azide anions. The structure of 2 shows 1D chains comprising alternating [(ipr2en)Cu-Ox-Cu(ipr2en)] units and end-to-end azide ligand. The chains on mutual H-bonding interaction through ClO4 −, give rise to a 2D supramolecular architecture. The magnetic data of complexes were recorded in the temperature range, 300–2 K. In case of complex 1, the magnetic data are consistent with a ferromagnetic interaction through the end-on azide bridge (JFM=10 cm−1) and a weak antiferromagnetic interaction (zj=−0.8 cm−1) between the ferromagnetically coupled dimers and an average g-value of 2.05. The susceptibility data of 2 were fitted using an alternating AF–AF chain spin 1/2 law which leads to the following parameters Joxalate=−180 cm−1, Jazide=−43 cm−1 and g=2.25 cm−1.