Search

The synthesis and characterization of new spin-crossover pyrazolato bridged dinuclear FeIINCSpy2μ-bpypz2 and the corresponding cyanotrihydroborato-κNcomplexes 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 andor Mössbauer 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.

This is the first report of a Ni(ii) complex with the six-membered IM2py chelate coordinating via oxygen, [Ni(acac)(tmen)(IM2py-κ2N,O)]PF₆ (1·PF₆) (acac = acetylacetonate; tmen = N,N,N',N'-tetramethylethylenediamine; IM2py = 2-(2-(pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy). This new complex 1·PF₆ has been synthesized by the direct reaction between [Ni(acac)(tmen)]PF₆ and IM2py. The X-ray analysis (monoclinic, P2₁/c, a = 15.378(2), b = 13.331(2), c = 16.560(2) Å, β = 116.377(6)°, Z = 4) demonstrated that the IM2py ligand is coordinated to Ni(ii) as an unprecedent six-membered didentate chelate with the κ2N,O mode in 1. The corresponding linkage isomer, [Ni(acac)(tmen)(IM2py-κ2N,N)]PF₆ (2·PF₆), was obtained from the deoxygenation reaction of [Ni(acac)(tmen)(NIT2py)]PF₆ with NaNO₂. Variable-temperature measurements of the magnetic susceptibility and UV-vis absorption bands indicated a ferromagnetic interaction in 2·PF₆ and an antiferromagentic one in 1·PF₆. These facts confirm a linkage isomeric pair of [Ni(acac)(tmen)(IM2py-κ2N,O)]+ (1) and [Ni(acac)(tmen)(IM2py-κ2N,N)]+ (2) with oxygen and nitrogen coordination, respectively, in the IM moiety.

Preparation and characterization by X-ray analysis and 2H NMR spectra have been described for twelve chromiumiii–nitroxide complexes of cis-Cracac2ClL and cis- and trans-Cracac2L2PF6with monodentate coordination through the pyridyl-N atom in the nitroxides, where acac pentane-2,4-dionate and L 4,4,5,5-tetramethyl-2-3- or 4-pyridylimidazolin-1-oxyl 3-oxide NIT3py or NIT4py and 4,4,5,5-tetramethyl-2-3- or 4-pyridylimidazolin-1-oxyl IM3py or IM4py. An intramolecular magnetic interaction between CrIIIand the nitroxide was found to be weakly antiferrromagnetic and ferromagnetic, respectively, in the NIT3py or IM3py complexes and the NIT4py or IM4py complexes. The difference in sign of these magnetic interaction constants between the 3- and 4-pyridyl-substituted nitroxides can be interpreted by a spin polarization mechanism for the π-electron system including the nitroxide SOMO π and CrIIIdπorbitals. The inherently weak magnetic interactions and absence of an intensity enhancement of the spin-forbidden d–d transition band in these nitroxides complexes are in contrast to our previous results for the chelated NIT2py 4,4,5,5-tetramethyl-2-2-pyridylimidazolin-1-oxyl 3-oxide and IM2py 4,4,5,5-tetramethyl-2-2-pyridylimidazolin-1-oxyl complexes. This may be accounted for by the difference in the mechanism of magnetic interactions; spin-polarization mechanism and exchange mechanism, respectively.

Two series of mononuclear LnIIIS- or RS-pbaHBpz32 Ln Tm, Er, Ho and dinuclear Ln2μ-S- or RS-pba4HBpz3−2 Ln Yb, Ho, Gd, Dy, Nd complexes pba RS- andor S-2-phenyl butyrate, HBpz3 hydrotrispyrazol-1-ylborate were prepared and their X-ray structures and NIR chiroptical properties investigated. Synthesis with a molar ratio 1 2 1 of Ln KHBpz3 pba results in the formation of either mono- or dinuclear complexes, depending on the Lniii ionic radii: mononuclear complexes from Ybiii to Hoiii and dinuclear ones from Dyiii to Ndiii. Only the dinuclear complexes for all of the Lniii studied were formed with a molar ratio 1 1 2 of Ln KHBpz3 pba. X-Ray structural analysis confirmed dinuclear structures with CHπ interactions and linear BLnLnB arrangements for the Lnμ-RS-pba4LnHBpz32Yb , Ho , Dy, Gd and Nd complexes and a skew bent arrangement of BLnLnB leading to configurational chirality in the Dyμ-S-pba4DyHBpz32complex. Comparison of NIR chiroptical spectra in the 4f–4f transitions with those of the corresponding Cr–Ln complexes, acac2CroxLnHBpz32 suggests that the 4f–4f CD intensities arise from configurational chirality, probably due to the skew bent BLnLnB disposition.