A tetracobalt(II) cluster with a two vertex truncated dicubane topology endogenously supported by carboxylate-based (2-pyridyl)methylamine ligands: magneto-structural and DFT studies

A reaction between CoCl2 and L3-(CO2-)2 (2 : 1 stoichiometry) in CH3OH affords a discrete complex [CoII4-{L3-(CO2-)2}2(μ3-OCH3)2(CH3OH)2(H2O)2Cl2] (1) [L3-(CO2-)2 = 3-[N-{2-(pyridin-2-yl)methyl}amino]-bis(propionate)]. The structure of 1 reveals two terminal mononuclear CoII{L3-(CO2-)2}Cl units connected by a dimeric CoII2(μ3-OCH3)2(CH3OH)2(H2O) unit present in the centre through two methoxo (μ3-OCH3)- and two carboxylate (μ-1,1-OCO-) bridges affording a tetranuclear coordination cluster of Co(II) with a defective dicubane topology. In 1, Co1 (terminal) has distorted octahedral CoIIN2O3Cl and the central Co2 has CoIIO6 coordination. Such coordination arrangements afford the observed topology. Variable-temperature magnetic studies reveal anti-ferromagnetic coupling in 1. Three magnetic exchange interactions (one anti-ferromagnetic and two ferromagnetic: J1 = +3.3 cm-1 (Co⋯Co 3.176 Å; μ-1,1-OCO- and μ3-OCH3 bridges), J2 = -2.5 cm-1 (Co⋯Co 3.228 Å; μ-1-OCO- and μ3-OCH3 bridges) and J3 = +10.6 cm-1 (Co⋯Co 3.084 Å; two μ3-OCH3 bridges)) have been identified, with the inclusion of the orbital reduction parameter (α = Aκ = 1.38), spin-orbit coupling (λ = -158 cm-1) and axial distortion (energy gap Δ = -975 cm-1 between singlet and doublet levels), rationalized by density functional theory (DFT) calculations.

Crystal structure of aqua-(1H-pyrazole-κN2)(pyridine-2,6-di-carboxyl-ato-κ3O2,N,O6)copper(II) dihydrate

In the title compound, [Cu(C7H3NO4)(C3H4N2)(H2O)]·2H2O, the CuII atom is coordinated by three O atoms and two N atoms, provided by a tridentate pyridine-2,6-di-carboxyl-ate (pdc), one pyrazole and one water ligand, forming a slightly distorted square-pyramidal geometry [range of O-Cu-O and O-Cu-N bond angles = 79.55 (8)-166.22 (10)°]. The water mol-ecule is positioned at the apical position. In the crystal, the complex mol-ecule and the two crystallographically independent non-coordinating water mol-ecules are linked into a supra-molecular layer structure parallel to the ab plane via O-H⋯O and N-H⋯O hydrogen bonds.

Crystal structure of catena-poly[[silver(I)-{μ-2,6-bis-[(1H-pyrazol-1-yl)meth-yl]pyridine-κ(3) N (1),N (2):N (2')}] nitrate]

In the title complex, {[Ag(C13H13N5)]NO3} n , the Ag(I) atom is coordinated by three N atoms from two bidentate/monodentate pyrazolylpyridyl ligands to form a distorted trigonal-planar geometry [range of angles: 83.34 (6) (chelate ring) to 139.15 (7) °]. The chelate ring has a distorted boat conformation. The dihedral angle between the pyridyl ring and the coordinating pyrazolyl ring is 67.22 (6)°. The non-coordinating pyrazolyl ring is twisted by 62.97 (7)° from the pyridyl ring. In the crystal, the complex cations are arranged in polymeric chains along the c-axis direction, with the nitrate counter-anions situated in between. Weak C-H⋯O hydrogen bonds link the ions into a three-dimensional network.

Dichlorido[1-(1-naphthyl-meth-yl)-3-(2-pyrid-yl)-1H-pyrazole-κN,N]palladium(II)

In the title compound, [PdCl(2)(C(19)H(15)N(3))], the Pd(II) centre is four-coordinated by two N-atom donors from one 1-[3-(2-pyrid-yl)pyrazol-1-ylmeth-yl]naphthalene (L) ligand and by two Cl atoms in a distorted square-planar coordination geometry. In the crystal structure, adjacent Pd(II) mononuclear units form inter-molecular C-H⋯π inter-actions involving the benzene and pyridine rings of different L ligands and π-π stacking inter-actions between the pyrazolyl-pyridine and naphthalene rings of neighbouring L ligands, with a centroid-centroid separation of 3.522 (1) Å.

Anion−Solvent Dependence of Bistability in a Family of Meridional N-Donor-Ligand-Containing Iron(II) Spin Crossover Complexes

Five mononuclear spin crossover iron(II) bis-meridional ligand complexes of the general formula [Fe(L)(2)](X)(2).solvent, have been synthesized, where X = BF(4)- or ClO(4)-; L = 2-(1-pyridin-2-ylmethyl-1H-pyrazol-3-yl)-pyrazine (picpzpz) or 2-(3-(2-pyridyl)pyrazol-1-ylmethyl)pyridine) (picpypz); solvent = MeOH or EtOH. The magnetic and structural consequences of systematic variation of meridional ligand, solvent, and anion, including a desolvated species, have been investigated. The complex [Fe(picpzpz)(2)](BF(4))(2).MeOH, 1.MeOH, displays several unique properties including a two-step spin transition with a gradual higher-temperature step ((1)T(1/2) = 197 K) and an abrupt low-temperature step with hysteresis ((2)T(1/2) = 91/98 K) and a metastable intermediate spin state below 70 K with quench-cooling. Removal of the solvent methanol results in the loss of the abrupt step and associated hysteresis (T(1/2) = 150 K). The complexes [Fe(picpzpz)(2)](BF(4))(2).EtOH (1.EtOH), [Fe(picpzpz)(2)](ClO(4))(2).MeOH (2.MeOH), [Fe(picpzpz)(2)](ClO(4))(2).EtOH (2.EtOH), and [Fe(picpypz)(2)](BF(4))(2).MeOH (3.MeOH) all show gradual one-step spin transitions with T(1/2) values in the range 210-250 K. Photomagnetic LIESST measurements on 1.MeOH reveal a near-quantitative excitation of high-spin sites and a unique two-step relaxation process related to the two-step thermal spin transition ((1)T(LIESST) = 49 K and (2)T(LIESST) = 70 K). The structural consequences of the unusual spin transition displayed by 1.MeOH have been investigated by single-crystal X-ray diffraction structural analyses between 25 and 293 K. Detailed characterization of the unit cell parameter evolution vs temperature reflects both the gradual high-temperature step and abrupt low-temperature step, including the thermal hysteresis, observed magnetically.

Magnetic behavior and Mössbauer spectra of spin-crossover pyrazolate bridged dinuclear diiron(ii) complexes: X-ray structures of high-spin and low-spin [{Fe(NCBH3)(py)}2(μ-bpypz)2]

The synthesis and characterization of new spin-crossover pyrazolato bridged dinuclear [(FeII(NCS)(py))2(mu-bpypz)2] and the corresponding cyanotrihydroborato-kappaN complexes are described together with the X-ray crystal analysis of the latter in both the high-spin and low-spin states as well as the variable temperature magnetic susceptibility and/or Mossbauer spectra demonstrating the spin-crossover which exhibits an one-step process, but not a two-step one characteristic of the known bpym bridged dinuclear complexes.