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In the crystal structure of the title compound, [Cu(NO 3 ) 2 (C 3 H 5 N 3 ) 4 ], the Cu II atom is situated on an inversion center (Wyckoff position 2 c of space group P 2 1 / n ) and shows an octa-hedral [N 4 O 2 ] coordination environment. The axial positions are occupied by O atoms of nitrate anions, while the equatorial positions are taken up by the N atoms of four 3-amino-pyrazole ligands. As a result of the tautomerism of the latter, two coordinate with the N 1 -atom of 3-amino-pyrazole while the other two with the N 2 -atom. The presence of pyrrole-like N-H groups and amine substituents as donor groups leads to numerous intra- and inter-molecular hydrogen-bonding inter-actions, which were qu-anti-fied by Hirshfeld surface analysis., (© Kucheriv et al. 2023.)

9-Amino-acridinium chloride N , N -di-methyl-formamide monosolvate, C 13 H 11 N 2 + Cl - ·C 3 H 7 NO, crystallizes in the monoclinic space group P 2 1 / c. The salt was crystallized from N , N -di-methyl-formamide. The asymmetric unit consists of two C 13 H 11 N 2 + Cl - formula units. The 9-amino-acridinium (9-AA) mol-ecules are protonated with the proton on the N atom of the central ring. This N atom is connected to an N , N -di-methyl-formamide mol-ecule by a hydrogen bond. The H atoms of the amino groups create short contacts with two chloride ions. The 9-AA cations in adjacent layers are oriented in an anti-parallel manner. The mol-ecules are linked via a network of multidirectional π-π inter-actions between the 9-AA rings, and the whole lattice is additionally stabilized by electrostatic inter-actions between ions., (© Fritsky et al. 2021.)

The title compound, [Cu 2 Cl 4 (C 5 H 10 N 2 O 2 ) 2 (CH 3 CN) 2 ] or [Cu 2 (μ 2 -Cl) 2 (CH 3 -Pz-COOCH 2 CH 3 ) 2 Cl 2 (CH 3 CN) 2 ], was synthesized using a one-pot reaction of copper powder, copper(II) chloride dihydrate and ethyl 5-methyl-1 H -pyrazole-3-carboxyl-ate (CH 3 -Pz-COOCH 2 CH 3 ) in aceto-nitrile under ambient conditions. This complex consists of discrete binuclear mol-ecules with a {Cu 2 (μ 2 -Cl) 2 } core, in which the Cu⋯Cu distance is 3.8002 (7) Å. The pyrazole-based ligands are bidentate coordinated, leading to the formation of two five-membered chelate rings. The coordination geometry of both copper atoms (ON 2 Cl 3 ) can be described as distorted octa-hedral on account of the aceto-nitrile coordination. A Hirshfeld surface analysis suggests that the most important contributions to the surface contacts are from H⋯H (40%), H⋯Cl/Cl⋯H (24.3%), H⋯O/O⋯H (11.8%), H⋯C/C⋯H (9.2%) and H⋯N/N⋯H (8.3%) inter-actions., (© Vynohradov et al. 2021.)

In the title metal-organic framework, [Fe(C 6 H 8 N 2 ) 2 {Cu(CN) 2 } 2 ] n , the low-spin Fe II ion lies at an inversion centre and displays an elongated octa-hedral [FeN 6 ] coordination environment. The axial positions are occupied by two symmetry-related bridging 2-ethyl-pyrazine ligands, while the equatorial positions are occupied by four N atoms of two pairs of symmetry-related cyanide groups. The Cu I centre is coordinated by three cyanide carbon atoms and one N atom of a bridging 2-ethyl-pyrazine mol-ecule, which form a tetra-hedral coordination environment. Two neighbouring Cu atoms have a short Cu⋯Cu contact [2.4662 (7) Å] and their coordination tetra-hedra are connected through a common edge between two C atoms of cyanide groups. Each Cu 2 (CN) 2 unit, formed by two neighbouring Cu atoms bridged by two carbons from a pair of μ-CN groups, is connected to six Fe II centres via two bridging 2-ethyl-pyrazine mol-ecules and four cyanide groups, resulting in the formation of a polymeric three-dimensional metal-organic coordination framework.

In the title polymeric complex, {[Fe(CN) 2 (C 10 H 8 N 2 ) 2 (H 2 O) 2 ][Au(CN) 2 ]} n , the Fe II ion, which is located on a twofold rotation axis, has a slightly distorted FeN 4 O 2 octa-hedral geometry. It is coordinated by two phenyl-pyrazine mol-ecules, two water mol-ecules and two di-cyano-aurate anions, the Au atom also being located on a second twofold rotation axis. In the crystal, the coordinated di-cyano-aurate anions bridge the Fe II ions to form polymeric chains propagating along the b -axis direction. In the crystal, the chains are linked by O water -H⋯N di-cyano-aurate anions hydrogen bonds and aurophillic inter-actions [Au⋯Au = 3.5661 (3) Å], forming layers parallel to the bc plane. The layers are linked by offset π-π stacking inter-actions [inter-centroid distance = 3.643 (3) Å], forming a supra-molecular metal-organic framework.

In the title metal-organic framework, [Fe(C 4 H 3 BrN 2 ) 2 {Cu(CN) 2 } 2 ] n , the Fe II cation is located on an inversion center and has a slightly elongated octa-hedral coordination environment [FeN 6 ], ligated by two pyrazine N atoms of symmetry-related bridging 2-bromo-pyrazine mol-ecules in the axial positions and by four N atoms of pairs of symmetry-related cyanido groups in the equatorial positions. The Cu I center has a fourfold coordination environment [CuC 3 N], with an almost perfect trigonal-pyramidal geometry, formed by three cyanido C atoms and an N atom of a bridging 2-bromo-pyrazine mol-ecule. Copper(I) centers related by a twofold rotation axis are bridged by two carbon atoms from a pair of μ-CN groups, resulting in Cu 2 (CN) 2 units. Each Cu 2 (CN) 2 unit is linked to six Fe II cations via a pair of linear CN units, the pair of μ-CN groups and two bridging 2-bromo-pyrazine ligands, resulting in the formation of a metal-organic framework, which is additionally stabilized by the short Cu⋯Cu contacts of 2.4450 (7) Å.

In the title polymeric complex, [Au 2 Fe(CN) 4 (C 4 H 3 IN 2 ) 2 (C 2 H 6 O)] n , the Fe II cation is coordinated by two iodo-pyrazine mol-ecules, one ethanol mol-ecule and three di-cyano-aurate anions in a distorted N 5 O octa-hedral geometry. In the crystal, the di-cyano-aurate anions bridge the Fe II cations to form polymeric chains propagating along the b- axis direction. Stabilization of the crystal structure is provided by O-H⋯N hydrogen bonds and π-π stacking between parallel iodo-pyrazine rings of neighbouring chains, the centroid-centroid distances being 3.654 (10) and 3.658 (9) Å.

In the title polymeric complex, [Fe{OS(CH 3 ) 2 } 2 {Ag(CN) 2 } 2 ], the Fe II cation is located at an inversion centre and is coordinated by four cyanide (CN - ) anions and two dimethyl sulfoxide mol-ecules in a slightly compressed N 4 O 2 octa-hedral geometry, the Ag I cation is C-coordinated by two CN - anions in a nearly linear geometry. The CN - anions bridge the Fe II and Ag I cations to form a two-dimensional polymeric structure extending parallel to (102). In the crystal, the nearest Ag⋯Ag distance between polymeric sheets is 3.8122 (12) Å. The crystal studied was a twin with a contribution of 0.2108 (12) for the minor component.

In the crystal of the title compound, [Fe(NCS)3(H2O)3]·3C6H8N2, the Fe(III) cation is located on a threefold rotation axis and is coordinated by three N atoms of the thiocyanate anions and three water mol-ecules in a fac arrangement, forming a slightly distorted N3O3 octa-hedron. Stabilization within the crystal structure is provided by O-H⋯N hydrogen bonds; the H atoms from coordinating water mol-ecules act as donors to the N atoms of guest 2,3-di-methyl-pyrazine mol-ecules, leading to a three-dimensional supra-molecular framework.