Long magnetic relaxation time of tetracoordinate Co2+ in imidazo[1,5-a]pyridinium-based (C13H12N3)2[CoCl4] hybrid salt and [Co(C13H12N3)Cl3] molecular complex

Triclinic polymorph of bis-[2-methyl-3-(pyridin-2-yl)imidazo[1,5-a]pyridin-2-ium] tetra-chloridocadmium(II)

The crystal structure of the title organic-inorganic hybrid salt, (C13H12N3)2[CdCl4], (I), has been reported with four mol-ecules in the asymmetric unit in a monoclinic cell [Vassilyeva et al. (2021 ▸). RSC Advances, 11, 7713-7722]. While using two different aldehydes in the oxidative cyclization-condensation involving CH3NH2·HCl to prepare a new monovalent cation with the imidazo[1,5-a]pyridinium skeleton, a new polymorph was obtained for (I) in space group P1 and a unit cell with approximately half the volume of the monoclinic form. The structural configurations of the two crystallographically non-equivalent organic cations as well as the geometry of the moderately distorted tetra-hedral CdCl4 2- dianion show minor changes. In the crystal, identically stacked cations and tetra-chloro-cadmate anions form separate columns parallel to the a axis. The loose packing of the anions leads to a minimal separation of approximately 9.53 Å between the metal atoms in the triclinic form versus 7.51 Å in the monoclinic one, indicating that the latter is packed slightly more densely. The two forms also differ by aromatic stacking motifs. Similar to the monoclinic polymorph, the triclinic one excited at 364 nm shows an intense unsymmetrical photoluminescent band with maximum at 403 nm and a full width at half maximum of 51 nm in the solid state.

Organic-inorganic hybrid hexa-chlorido-stannate(IV) with 2-methyl-imidazo[1,5-a]pyridin-2-ium cation

The hybrid salt bis-(2-methyl-imidazo[1,5-a]pyridin-2-ium) hexa-chlorido-stannate(IV), (C8H9N2)2[SnCl6], crystallizes in the monoclinic space group P21/n with the asymmetric unit containing an Sn0.5Cl3 fragment (Sn site symmetry ) and one organic cation. The five- and six-membered rings in the cation are nearly coplanar; bond lengths in the pyridinium ring of the fused core are as expected; the C-N/C bond distances in the imidazolium entity fall in the range 1.337 (5)-1.401 (5) Å. The octa-hedral SnCl6 2- dianion is almost undistorted with the Sn-Cl distances varying from 2.4255 (9) to 2.4881 (8) Å and the cis Cl-Sn-Cl angles approaching 90°. In the crystal, π-stacked chains of cations and loosely packed SnCl6 2- dianions form separate sheets alternating parallel to (101). Most of the numerous C-H⋯Cl-Sn contacts between the organic and inorganic counterparts with the H⋯Cl distances above the van der Waals contact limit of 2.85 Å are considered a result of crystal packing.

Magnetic anisotropy of two tetrahedral Co(II)-halide complexes with triphenylphosphine ligands

Recently, the choice of ligand and geometric control of mononuclear complexes, which can affect the relaxation pathways and blocking temperature, have received wide attention in the field of single-ion magnets (SIMs). To find out the influence of the coordination environment on SIMs, two four-coordinate mononuclear Co(II) complexes [NEt₄][Co(PPh₃)X₃] (X = Cl^-, 1; Br^-, 2) have been synthesized and studied by X-ray single crystallography, magnetic measurements, high-frequency and -field EPR (HF-EPR) spectroscopy and theoretical calculations. Both complexes are in a cubic space group Pa3̄ (No. 205), containing a slightly distorted tetrahedral moiety with crystallographically imposed C_3v symmetry through the [Co(PPh₃)X₃]^- anion. The direct-current (dc) magnetic data and HF-EPR spectroscopy indicated the anisotropic S = 3/2 spin ground states of the Co(II) ions with the easy-plane anisotropy for 1 and 2. Ab initio calculations were performed to confirm the positive magnetic anisotropies of 1 and 2. Frequency- and temperature-dependent alternating-current (ac) magnetic susceptibility measurements revealed slow magnetic relaxation for 1 and 2 at an applied dc field. Finally, the magnetic properties of 1 and 2 were compared to those of other Co(II) complexes with a [CoAB₃] moiety.

Magnetic anisotropies and slow magnetic relaxation of three tetrahedral tetrakis(pseudohalido)–cobalt(ii) complexes

Magnetic anisotropies and slow magnetic relaxation of three homoleptic cobalt(ii) complexes with different pseudohalide ligands were studied via magnetometry, HFEPR and theoretical calculations.

Single molecule magnet behaviour in a square planar S = 1/2 Co(ii) complex and spin-state assignment of multiple relaxation modes

We report the first example of field-induced single molecule magnet (SMM) behaviour in a square-planar S = 1/2 Co(ii) pincer complex [(PNNNP)CoBr]Br (2). The related five-coordinate complexes [(PCNCP)CoBr2] (1) and [(PONOP)CoBr2] (3) also exhibit SMM properties. Partial spin crossover displayed by 3 allows for assignment of distinct relaxation modes to each spin state.

Crystal structure and characterization of a new copper(II) chloride dimer with meth-yl(pyridin-2-yl-methyl-idene)amine

The new copper(II) complex, namely, di-μ-chlorido-bis-{chlorido-[meth-yl(pyri-din-2-yl-methyl-idene)amine-κ2 N,N']copper(II)}, [Cu2Cl4(C7H8N2)2], (I), with the ligand 2-pyridyl-methyl-N-methyl-imine (L, a product of Schiff base condensation between methyl-amine and 2-pyridine-carbaldehyde) is built of discrete centrosymmetric dimers. The coordination about the CuII ion can be described as distorted square pyramidal. The base of the pyramid consists of two nitro-gen atoms from the bidentate chelate L [Cu-N = 2.0241 (9), 2.0374 (8) Å] and two chlorine atoms [Cu-Cl = 2.2500 (3), 2.2835 (3) Å]. The apical position is occupied by another Cl atom with the apical bond being significantly elongated at 2.6112 (3) Å. The trans angles of the base are 155.16 (3) and 173.79 (2)°. The Cu⋯Cu separation in the dimer is 3.4346 (3) Å. In the crystal structure, the loosely packed dimers are arranged in stacks propagating along the a axis. The X-band polycrystalline 77 K EPR spectrum of (I) demonstrates a typical axial pattern characteristic of mononuclear CuII complexes. Compound (I) is redox active and shows a cyclic voltammetric response with E 1/2 = -0.037 V versus silver-silver chloride electrode (SSCE) assignable to the reduction peak of CuII/CuI in methanol as solvent.

Crystal structure of imidazo[1,5-a]pyridinium-based hybrid salt (C13H12N3)2[MnCl4]

A new organic-inorganic hybrid salt [L]2[MnCl4] (I) where L + is the 2-methyl-3-(pyridin-2-yl)imidazo[1,5-a]pyridinium cation, is built of discrete organic cations and tetra-chlorido-manganate(II) anions. The L + cation was formed in situ in the oxidative cyclo-condensation of 2-pyridine-carbaldehyde and CH3NH2·HCl in methanol. The structure was refined as a two-component twin using PLATON (Spek, 2020 ▸) to de-twin the data. The twin law (-1 0 0 0 - 1 0 0.5 0 1) was applied in the refinement where the twin component fraction refined to 0.155 (1). The compound crystallizes in the space group P21/c with two crystallographically non-equivalent cations in the asymmetric unit, which possess similar structural conformations. The fused pyridinium and imidazolium rings of the cations are virtually coplanar [dihedral angles are 0.89 (18) and 0.78 (17)°]; the pendant pyridyl rings are twisted by 36.83 (14) and 36.14 (13)° with respect to the planes of the remaining atoms of the cations. The tetra-hedral MnCl4 2- anion is slightly distorted with the Mn-Cl distances falling in the range 2.3469 (10)-2.3941 (9) Å. The distortion value of 0.044 relative to the ideal tetra-hedron was obtained by continuous shape measurement (CShM) analysis. In the crystal, the cations and anions form separate stacks propagating along the a-axis direction. The organic cations display weak π-π stacking. The anions, which are stacked identically one above the other, demonstrate loose packing; the minimum Mn⋯Mn separation in the cation stack is approximately 7.49 Å. The investigation of the fluorescent properties of a powdered sample of (I) showed no emission. X-band EPR data for (I) at 293 and 77 K revealed broad fine structure signals, indicating moderate zero-field splitting.

Synthetic strategy towards halometallates with imidazo[1,5-a]pyridinium-based counterions

The interaction between formaldehyde, amine and 2-pyridinecarbaldehyde with MX_n (X = halide) in the presence of HX enables creation of a large range of chemical and structural variations for systematic investigation of the entailing properties.

Crystal structures of an imidazo[1,5-a]pyridinium-based ligand and its (C13H12N3)2[CdI4] hybrid salt

The monocation product of the oxidative condensation-cyclization between two mol-ecules of pyridine-2-carbaldehyde and one mol-ecule of CH3NH2·HCl in methanol, 2-methyl-3-(pyridin-2-yl)imidazo[1,5-a]pyridinium, was isolated in the presence of metal ions as bis-[2-methyl-3-(pyridin-2-yl)imidazo[1,5-a]pyridin-2-ium] tetra-iodo-cadmate, (C13H12N3)2[CdI4], (I), and the mixed chloride/nitrate salt, bis-[2-methyl-3-(pyridin-2-yl)imidazo[1,5-a]pyridin-2-ium] 1.5-chlor-ide 0.5-nitrate trihydrate, 2C13H12N3 +·1.5Cl-·0.5NO3 -·3H2O, (II). Hybrid salt (I) crystallizes in the space group P21/n with two [L]2[CdI4] mol-ecules in the asymmetric unit related by pseudosymmetry. In the crystal of (I), layers of organic cations and of tetra-halometallate anions are stacked parallel to the ab plane. Anti-parallel L + cations disposed in a herring-bone pattern form π-bonded chains through aromatic stacking. In the inorganic layer, adjacent tetra-hedral CdI4 units have no connectivity but demonstrate close packing of iodide anions. In the crystal lattice of (II), the cations are arranged in stacks propagating along the a axis; the one-dimensional hydrogen-bonded polymer built of chloride ions and water mol-ecules runs parallel to a column of stacked cations.

Slow magnetic relaxation in a high-spin pentacoordinate Fe(iii) complex

A mononuclear pentacoordinate iron(iii) complex shows slow magnetic relaxation with three relaxation channels.