Two CuII complexes of 3,4,5-tri-methyl-1H-pyrazole.

The crystal structure of complexes of 3,4,5-tri-methyl-1H-pyrazole with CuCl2·2H2O and Cu(NO3)2·2.5H2O are presented, namely di-µ-chlorido-bis[chloridobis(3,4,5-trimethyl-1H-pyrazole-κN2)copper(II)], [Cu2Cl4(C6H10N2)4] (1) and aquatetrakis(3,4,5-trimethyl-1H-pyrazole-κN2)copper(II) dinitrate, [Cu(C6H10N2)4(H2O)](NO3)2 (2), and compared to the previously determined structures for 3-methyl-1H-pyrazole and 3,5-di-methyl-1H-pyrazole. CuCl2 forms a 2:1 ligand-to-metal chloride-bridged complex with 3,4,5-tri-methyl-1H-pyrazole, with a square-pyramidal coordination geometry about each copper(II) center. Similarly to the previously obtained 3,5-di-methyl-1H-pyrazole complex with CuCl2, the pyrazole ligands are cis to each other, with two chloride ions bridging the two copper(II) centers, and a terminal chloride ion occupying the axial position. Cu(NO3)2 forms a 4:1 ligand-to-metal complex with 3,4,5-tri-methyl-1H-pyrazole that is also arranged in a square-pyramidal geometry about CuII. The newly obtained copper(II) complex has the same coordination geometry as the 3,5-di-methyl-1H-pyrazole complex, including an axial water mol-ecule, two nitrate ions hydrogen-bonded to the water mol-ecule, and four pyrazole ligands in the equatorial plane, suggesting that similar steric forces are at play in the formation of these complexes.

Effect of counter-ion on packing and crystal density of 5,5'-(3,3'-bi[1,2,4-oxa-diazole]-5,5'-di-yl)bis-(1H-tetra-zol-1-olate) with five different cations.

In energetic materials, the crystal density is an important parameter that affects the performance of the material. When making ionic energetic materials, the choice of counter-ion can have detrimental or beneficial effects on the packing, and therefore the density, of the resulting energetic crystal. Presented herein are a series of five ionic energetic crystals, all containing the dianion 5,5'-(3,3'-bi[1,2,4-oxa-diazole]-5,5'-di-yl)bis-(1H-tetra-zol-1-olate), with the following cations: hydrazinium (1) (2N2H5+·C6N12O42-), hydroxyl-ammonium (2) 2NH4O+·C6N12O42- [Pagoria et al.. (2017). Chem. Heterocycl. Compd, 53, 760-778; included for comparison], di-methyl-ammonium (3) (2C2H8N+·C6N12O42-), 5-amino-1H-tetra-zol-4-ium (4) (2CH4N5+·C6N12O42-·4H2O), and amino-guanidinium (5) (2CH7N4+·C6N12O42-). Both the supra-molecular inter-actions and the sterics of the cation play a role in the density of the resulting crystals, which range from 1.544 to 1.873 Mg m-1. In 5, the tetra-zolate ring is disordered over two positions [occupancy ratio 0.907 (5):0.093 (5)] due to a 180° rotation in the terminal tetra-zole rings.

Supramolecular architectures with π-acidic 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine cavities: role of anion-π interactions in the remarkable stability of Fe(II) metallacycles in solution.

The comprehensive investigation reported herein provides compelling evidence that anion-π interactions are the main driving force in the formation of self-assembled Fe(II)-templated metallacycles with bptz [3,6-bis(2-pyridyl)-1,2,4,5-tetrazine] in high yields. It was demonstrated by X-ray crystallography, (1)H NMR, solution and solid-state MAS (19)F NMR spectroscopies, CV and MS studies that the anions [X](-) = [BF(4)](-), [ClO(4)](-) and the anions [Y](-) = [SbF(6)](-), [AsF(6)](-), [PF(6)](-) template molecular squares [Fe(4)(bptz)(4)(CH(3)CN)(8)][X](8) and pentagons [Fe(5)(bptz)(5)(CH(3)CN)(10)][Y](10), respectively. The X-ray structures of [{Fe(4)(bptz)(4)(CH(3)CN)(8)}⊂BF(4)][BF(4)](7) and [{Fe(5)(bptz)(5)(CH(3)CN)(10)}⊂2SbF(6)][SbF(6)](8) revealed that the [BF(4)](-) and [SbF(6)](-) anions occupy the π-acidic cavities, establishing close directional F···C(tetrazine) contacts with the tetrazine rings that are by ~0.4 Å shorter than the sum of the F···C van der Waals radii (ΣR(vdW) F···C = 3.17 Å). The number and strength of F···C(tetrazine) contacts are maximized; the F···C(tetrazine) distances and anion positioning versus the polygon opposing tetrazine rings are in agreement with DFT calculations for C(2)N(4)R(2)···[X](-)···C(2)N(4)R(2) (R = F, CN; [X](-) = [BF(4)](-), [PF(6)](-)). In unprecedented solid-state (19)F MAS NMR studies, the templating anions, engaged in anion-π interactions in the solid state, exhibit downfield chemical shifts Δδ((19)F) ≈ 3.5-4.0 ppm versus peripheral anions. NMR, CV, and MS studies also establish that the Fe(II) metallacycles remain intact in solution. Additionally, interconversion studies between the Fe(II) metallacycles in solution, monitored by (1)H NMR spectroscopy, underscore the remarkable stability of the metallapentacycles [Fe(5)(bptz)(5)(CH(3)CN)(10)][PF(6)](10) ≪ [Fe(5)(bptz)(5)(CH(3)CN)(10)][SbF(6)](10) < [Fe(5)(bptz)(5)(CH(3)CN)(10)][AsF(6)](10) versus [Fe(4)(bptz)(4)(CH(3)CN)(8)][BF(4)](8), given the inherent angle strain in five-membered rings. Finally, the low anion activation energies of encapsulation (ΔG(‡) ≈ 50 kJ/mol), determined from variable-temperature (19)F NMR studies for [Fe(5)(bptz)(5)(CH(3)CN)(10)][PF(6)](10) and [Zn(4)(bptz)(4)(CH(3)CN)(8)][BF(4)](8), confirm anion encapsulation in the π-acidic cavities by anion-π contacts (~20-70 kJ/mol).

Anion-templated self-assembly of highly stable Fe(II) pentagonal metallacycles with short anion-π contacts.

The crystal structures of the self-assembled metallapentacycles [{Fe(5)(bptz)(5)(CH(3)CN)(10)} ⊂ 2SbF(6)][SbF(6)](8) (1) and [{Fe(5)(bmtz)(5)(CH(3)CN)(10)} ⊂ SbF(6)][SbF(6)](9) (2) with the π-acidic ligands bptz (3,6-bis(2-pyridyl)-1,2,4,5-tetrazine) and bmtz (3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine), respectively, revealed cationic pentagons templated by [SbF(6)](-) ions. The short anion-π contacts established between the anions and the tetrazine rings play an important role in the stability of the pentagons.

Solvent-enhanced magnetic ordering temperature for mixed-valent chromium hexacyanovanadate(II), Cr(II)0.5Cr(III)[V(II)(CN)6].zMeCN, magnetic materials.

The reaction of V(III)(THF)3Cl3 with NEt(4)CN in acetonitrile (MeCN) forms (NEt4)3[V(III)(CN)6].4MeCN (1), which after characterization was used as a molecular building block toward the synthesis of Prussian blue structured magnets. The reaction of 1 with [Cr(II)(NCMe)4](BF4)2 forms Cr(II)(0.5)Cr(III)[V(II)(CN)6].zMeCN via internal electron transfer, whose structure and magnetic properties are dependent on the degree of solvation, z. When solvated, Cr(II)(0.5)Cr(III)[V(II)(CN)6].1.2MeCN (2) is a mixture of crystalline and amorphous fractions that yield a material with two magnetic phases: bulk ferrimagnetic phase/crystalline [faced-centered-cubic lattice with a = 10.55(2) A] and cluster-glass phase/amorphous. The bulk ferrimagnetic phase exhibits a critical temperature, Tc, of 110 K, while the amorphous cluster-glass phase exhibits a freezing temperature, Tf, of approximately 25 K. Amorphous Cr(II)(0.5)Cr(III)[V(II)(CN)6].0.1MeCN (3) was determined to be the pure cluster-glass phase. This is an overall enhancement of 85 K (350%) in the magnetic ordering temperature via solvation, z. The coercivity was also increased 4-fold from 890 (2) and 3900 Oe (3) via desolvation.