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Four air-stable mononuclear Co(II) complexes, with the formulas [Co(dapbh)(H2O)(CH3OH)] (1), [Co(Hdapbh)(N3)(CH3OH)]·(CH3OH) (2), [Co(H2aapbh)(CH3OH)2]·(NO3)2 (3) and [Co(H2bapbh)(H2O)(NO3)]·(NO3) (4), have been synthesized and structurally characterized by single crystal X-ray diffraction. In all of the complexes, the Co(II) centers constrained by the rigid pentadentate ligand H2LR with two protonable hydrogens adopt a heptacoordinated pentagonal-bipyramidal geometry. The combined analyses of magnetic data and ab initio calculations unveil large easy-plane magnetic anisotropies for these complexes (D = +37.338, +37.273, +41.138 and +41.139 cm−1 for 1–4, respectively), which indicate that the chemical alterations of the equatorial ligand and the ligand field strength in the axial positions synergistically fine-tune the magnitude of the D values. Magnetic investigations demonstrate the field-induced single-ion magnetic behavior in complexes 1, 2 and 4 with diverse energy barriers (Ueff) of 12.25 for 1, 44.15 for 2 and 48.72 K for 4, corresponding to the geometrical distortion of the heptacoordinated Co(II) ion. That is, the greatest deviation from the ideal D5h symmetry in 4 is responsible for the highest barrier. [ABSTRACT FROM AUTHOR]

In the presence of different nitrogen-rich ligands, two energetic MOFs with formulas [Ag(tza)]n (1) and [Ag(atza)]n (2) (Htza = tetrazole-1-acetic acid and Hatza = (5-amino-1H-tetrazole-1-yl) acetic acid) were successfully synthesized and characterized. X-ray single crystal structure analysis shows that both 1 and 2 have 2D layer-like topologies. The experimental and theoretical evaluations reveal the promising properties of both energetic compounds, such as prominent heats of detonation, high thermal stabilities, good sensitivities and excellent detonation performances. In contrast to 1, interestingly, the introduction of the amino group in 2 leads to various coordination modes of the ligands and different stacking patterns of the frameworks, resulting in the observation of the shorter Ag–O, Ag–Ag, C–N, N–N, and N＝N bond lengths in 2. Consequently, 2 features superior heats of detonation and thermostability compared to 1. The nonisothermal thermokinetic parameters are obtained by using the Kissinger and Ozawa methods, while the standard molar enthalpies of formation are calculated from the determination of constant volume combustion energies. In addition, both compounds were explored as practical additives to promote the thermal decomposition of ammonium perchlorate (AP). This work may provide an effective approach for manipulating the energetic properties and thermostability of high-energy compounds via the perturbation of energetic groups. [ABSTRACT FROM AUTHOR]

Complexation of dysprosium(III) ions with a multidentate hydrazone ligand, N-[(E)-pyridin-2-ylmethylideneamino]pyridine-2-carboxamide (L), in the presence of different β-diketonate coligands, leads to the formation of two novel DyIII dimers, with formulas Dy2(BTFA)4(L)2 (1) and Dy2(TTA)4(L)2 (2) (BTFA = 3-benzoyl-1,1,1-trifluoroacetone and TTA = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate). They exhibit slightly different coordination geometries around DyIII centers and discrepant binuclear motifs – as a result of altering the β-diketonate coligands – which has an impact on the magnetic interactions between metal centers, the local tensor of anisotropy on each DyIII site and their relative orientations, therefore contributing to distinct magnetization dynamics. Compared to 2, complex 1 exhibits a more significant slow magnetic relaxation of SMM behavior in the absence of a dc field. The QTM effect is effectively repressed under a static field, resulting in the energy barriers of 57 K for 1 and 38 K for 2. Ab initio calculations clarify that, strong single-ion magnetic anisotropies exist in both complexes, whereas intermetallic ferromagnetic interaction and antiferromagnetic interaction are observed in 1 and 2, respectively, therefore resulting in dissimilar magnetization dynamics. [ABSTRACT FROM AUTHOR]

The utilization of two isomorphic ligands with different substituents leads to two centrosymmetric DyIII dimers, namely, [Dy2(bfbpen)2(H2O)2]·2I− (1) and [Dy2(bcbpen)2(H2O)2]·2I−·0.5H2O (2) (H2bfbpen = N,N′-bis-(2-hydroxy-5-fluoro-benzyl)-N,N′-bis-(pyridin-2-ylmethyl)ethylenediamine and H2bcbpen = N,N′-bis-(2-hydroxy-5-chloro-benzyl)-N,N′-bis-(pyridin-2-ylmethyl)ethylenediamine). Although Dy ions in both compounds uniformly exhibit a square-antiprism geometry, the critical difference found in the terminal substituents of the two ligands fine-tunes the local crystal field around Dy centers and the dinuclear molecular structures of 1 and 2. Magnetic investigations unveil that both 1 and 2 display dynamic magnetic relaxation of single-molecule magnet (SMM) behaviour with different energy barriers of 20.9 K for 1 and 72.7 K for 2 under a zero direct-current (dc) field, as well as 26.9 K for 1 under a 1200 Oe dc field. Compared to 1, the stronger uniaxial anisotropy and magnetic exchange in 2 render it a better SMM as evidenced by the higher energy barrier. Ab initio calculations are also performed on both Dy2 compounds to rationalize the observed discrepancy in their magnetic behaviours. The contribution illustrates that the SMM behaviour could be effectively enhanced by means of deliberate local structural manipulation. [ABSTRACT FROM AUTHOR]

A family of four mononuclear DyIII β‐diketonate complexes with formulas [Dy(tmhd)3(Br2‐bpy) (1), [Dy(tmhd)3(Br‐bpy)] (2), [Dy(tmhd)3(dppz)] (3), and [Dy(tmhd)3(mcdpq)] (4) (tmhd=2,2,6,6‐tetramethyl‐3,5‐heptanedione, Br2‐bpy=5,5′‐dibromo‐2,2′‐bipyridine, Br‐bpy=5‐bromo‐2,2′‐bipyridine, dppz=dipyrido [3,2‐a:2′,3′‐c]phenazine, mcdpq=2‐methoxyl‐3‐cyanodipyrido[3,2‐f:2,3′‐h]quinoxaline) were prepared by modifying the capping N‐donor coligands. DyIII centers in these complexes feature an N2O6 octacoordinate environment with distorted square‐antiprismatic D4d symmetry. Magnetic investigations evidenced single‐ion magnet behavior in all complexes with energy barriers Ueff of 42.10 (1), 61.47, (2), 77.53 (3), and 2.51 K (4) in the absence of static field, as well as 206.03 (1), 224.13 (2), 247.76 (3), and 49.70 K (4) under applied dc field (Hdc=1500 Oe for 1 and 2; Hdc=1200 Oe for 3 and 4). The different natures of the N‐donor ligands induce changes in both the coordination geometry and their intermolecular interactions, which severely impact their magnetic dynamics. The disparities in their magnetic behaviors and the uniaxial anisotropies are also explained and substantiated by theoretical calculations. Cap variations: A combination of electron‐donating β‐diketonate ligands and different capping N‐donor coligands led to a family of four mononuclear DyIII complexes exhibiting nearly identical D4d symmetry but differing magnetic dynamics, which were elucidated by a combination of magnetic investigations and ab initio calculations. [ABSTRACT FROM AUTHOR]

A β-diketonate mononuclear dysprosium compound, [Dy(TFNB)3(bpy)] (1) (TFNB = 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione, bpy = 2,2′-bipyridine), has been prepared and structurally and magnetically characterized. X-ray crystallographic analysis reveals that 1 contains two crystallographically equivalent Dy(III) ions of which the eight-coordinate geometries uniformly behave as distorted square antiprismatic configurations (D4d). Magnetic investigations demonstrate that 1 displays dual relaxation processes of SMMs behavior with the effective barrier (ΔE/kB) of 23.44 K under 1200 Oe DC field, corresponding to the coexistence of two metal centers in the structure of the compound. The comparative studies of some Dy(III)-based SIMs with TFNB ligand have been conducted as well. Ab initio studies demonstrate that the Kramers doublet ground state is predominantly axial with the gz tensors of two Dy(III) fragments matching the Ising-limit factor (20) anticipated for the pure MJ = ±15/2 state. [ABSTRACT FROM AUTHOR]

Based on 2-(4-carboxyphenyl)imidazo[4,5-f]-1,10-phenanthroline (HNCP) and 2,5-thiophenedicarboxylate (TDC2−) ligands, three new lanthanide-containing (Sm, Nd, and Pr) compounds, [Sm(NCP)(TDC)]n (1), [Nd(NCP)(TDC)]n·2n(H2O)0.5 (2), and [Pr(NCP)(TDC)]n·n(H2O)0.5 (3), have been synthesized using the hydrothermal method and structurally characterized using single-crystal X-ray diffraction. Structural analyses have revealed that compounds 1–3 are 3D isostructural metal-organic frameworks in which the [Ln2(COO)4] dimers can be regarded as 6-connecting nodes, and the TDC2− and NCP− ligands are simplified as connectors to achieve the double interspersed 3D networks with the point symbol {412·63}. Thermogravimetric analysis has illustrated that the rigid architecture contributes to superior thermal stability with a thermal decomposition temperature of more than 400°C for the resulting metal-organic frameworks. [ABSTRACT FROM AUTHOR]

Employing different benzendicarboxylic acids as co-ligands, two new compounds, [Cu 2 (bpad) 2 (Hp) 2 ] n ( 1 ) and [Cu 2 (bpad) 2 (Hip) 2 ] n ( 2 ) (Hbpad = N 3 -benzoylpyridine-2-carboxamidrazone, H 2 p = phthalic acid, H 2 ip = isophthalic acid), have been synthesized. The structures and magnetic properties of title compounds have been systematically characterized. The two dinuclear Cu(II) compounds are isomers in which the metal ions adopt distinguishably penta-coordinated geometries. Cu(II) ions with square pyramidal structure are bridged by carboxylate oxygen atoms in 1 , while the Cu(II) centers with trigonal bipyramid model are linked by carbamoyl oxygen atoms in 2 . Magnetic measurements illustrate that the short contacts causing antiferromagnetic intra-dimer interactions consist in compound 1 , whereas ferromagnetic intra-dimer interactions are performed on compound 2 . [ABSTRACT FROM AUTHOR]

A new Co(II)-based compound with a 3-phenyl-5-(pyridin-4-yl)-1,2,4-triazole (4-Hppt) and isophthalic acid (H2ip) mixed ligand, [Co(4-Hppt)2(ip)] ( 1), has been synthesized and structurally and magnetically characterized. The structure of compound 1 consists of one-dimensional coordination chains based on the Co2 units bridged by dual carboxylate groups, where the pyridyl nitrogen atoms in 4-Hppt ligands are located in the axial coordination sites of the octahedral Co(II) nodes. Magnetic investigation suggests that the magnetic coupling derived from the dinuclear Co(II) ions is a moderately antiferromagnetic exchange in the title compound. Moreover, DFT calculations have been performed on the compound to offer a qualitatively theoretical explanation of the magnetic behavior. [ABSTRACT FROM AUTHOR]

A 3D metal–organic framework (MOF), {[Cd 2 (CTA)(bpp) 2 (H 2 O) 2 ] (H 2 O) 3 } n ( 1 ) (H 4 CTA = cyclohexane-1,2,4,5-tetracarboxylic acid, bpp = 1,3-bis(4-pyridyl)propane), has been synthesized and structurally characterized by elemental analysis, IR and powder X-ray diffraction. Single-crystal X-ray measurement reveals that the complex presents three-dimensional frameworks with 1D channels which are filled by unique (H 2 O) 6 clusters. Noteworthily, the H 4 CTA ligands keep exclusive conformation, where the carboxyl groups adopt different coordination modes, and the bpp ligands perform two different conformations. Thermogravimetric analysis demonstrates that 1 features favorable thermal stability. Photoluminescence property of 1 is investigated in the solid state at room temperature as well. [ABSTRACT FROM AUTHOR]

An alternative method to prepare new-generation green high-energy-density materials with excellent performances has been developed on the basis of a coordination chemistry strategy. In the present work, hydrothermal reaction of Cu(ii)/Cu(i) with a rigid nitrogen-rich ligand, 3-(1H-tetrazol-5-yl)-1H-triazole (H2tztr), led to three high-energy metal–organic frameworks (MOFs): [Cu(Htztr)2(H2O)2]n (1), {[Cu(tztr)]·H2O}n (2) and [Cu(Htztr)]n (3). Referring to the coordination geometry configuration of Cu(ii)/Cu(i) and flexible coordination fashion of the ligand, the energies of the complexes 1–3 are gradually improved when they are structurally transformed from 1, a mononuclear structure to 2, a 3D porous MOF incorporated with guest water molecules to 3, a well-isolated layer structure. The title complexes show outstanding thermostability (Tdec = 345 °C for 1, 325 °C for 2 and 355 °C for 3) and low sensitivity, confirmed by experimental and theoretical characterization. Notably, complex 3 features superior detonation properties to that of known energetic MOFs. [ABSTRACT FROM AUTHOR]

Reaction of Co(II) with the nitrogen-rich ligand N, N-bis(1 H-tetrazole-5-yl)-amine (H2bta) leads to a mixed-valence, 3D, porous, metal-organic framework (MOF)-based, energetic material with the nitrogen content of 51.78%, [Co9(bta)10(Hbta)2(H2O)10] n⋅(22 H2O) n ( 1). Compound 1 was thermohydrated to produce a new, stable, energetic material with the nitrogen content of 59.85% and heat of denotation of 4.537 kcal cm−3, [Co9(bta)10(Hbta)2(H2O)10] n ( 2). Sensitivity tests show that 2 is more sensitivity to external stimuli than 1, reflecting guest-dependent energy and sensitivity of 3D, MOF-based, energetic materials. Less-sensitive 1 can be regarded as a more safe form for storage and transformation to sensitive 2. [ABSTRACT FROM AUTHOR]

Abstract A Co(II)-containing complex of formula [Co 2 (3-fba) 4 (4,4′-bpy) 3 (CH 3 OH) 2 ] (1), has been prepared and structurally characterized by single-crystal X-ray crystallography (3-Hfba = 3-fluorobenzoic acid, 4,4′-bpy = 4,4′-bipyridine). The title complex is composed of well-isolated bimetallic moieties where two octahedral high-spin Co(II) ions are spatially separated from each other by bipyridyl bridges. As a result, the complex features field-induced single-ion magnet behavior with the effective energy barrier of 22.8 K. Graphical abstract A new Co(II)-based complex in which the metal centers display hexa-coordinated octahedral geometry performs field-induced single-ion magnet behavior. Unlabelled Image Highlights • A new Co(II)-containing complex has been obtained with mixed ligands of carboxylate and bipyridine. • The hexa-coordinated Co(II) ions with octahedral geometry are well-isolated in the complex. • The complex exhibits field-induced single-ion magnet behavior. [ABSTRACT FROM AUTHOR]

With the increased electron donating effect on carboxylic acid substituents, the ferromagnetic interaction between the paramagnetic centres was enhanced, whereas the contribution of the antiferromagnetic interaction was reduced. • The calculations at the B3LYP/def2-TZVP level could describe the magnetic properties of the azide copper complex accurately. • Magnetic orbits were mainly composed of orbits 3 d z2 of Cu(1)/Cu(2) and the -type molecular orbital. • With the increased electron donating effect on carboxylic acid substituents, the ferromagnetic interaction between the paramagnetic centres was enhanced, whereas the contribution of the antiferromagnetic interaction was reduced. The magnetic properties of the azide copper complex [Cu 2 (dpyam) 2 (μ 1,1 -N 3) 2 (O 2 CCH 3) 2 were studied using the density functional theory-broken symmetry methodology under different functional methods and basis sets. The magnetic coupling constant between paramagnetic centres was calculated as 36.75 cm−1, which agreed with the experimental value of 31.9 cm−1. Accordingly, the calculations at the B3LYP/def2-TZVP level could describe the magnetic properties of the azide copper complex accurately. To study thoroughly the effect of carboxylic acid auxiliary ligands in azido-Cu(II) systems, acetas were deleted from the auxiliary ligands(1) and replaced by H 2 O-(2), HCOO-(3), CH 3 COO-(4), C 2 H 5 COO-(5), and C 6 H 5 COO-(6), yielding six research models. With the increased electron donating effect on carboxylic acid substituents, the ferromagnetic interaction between the paramagnetic centres was enhanced, whereas the contribution of the antiferromagnetic interaction was reduced. The parameters ρ HS 2 - ρ BS 2 , S ab 2 , and (ε 1 - ε 2) 2 can be extended to other binuclear complexes for the study of magneto-structural correlation. [ABSTRACT FROM AUTHOR]