Dinuclear nickel complexes of phenolbased dinucleating macrocycles: Synthesis,structure, and properties

Abstract

Dinuclear Ni₂(II,II) complexes with the formula [Ni₂(R^m,n)](ClO₄)₂ ((m,n)= (2,2) (1), (2,3) (2), (2,4) (3)) have been obtained where (R^m,n)^2- denotes the macrocycles containing two 2,6-bis(iminomethyl)-4-methylphenolate entities combined through two lateral chains, -(CH₂)_m- and -(CH₂)_n-, at the imino nitrogens. [Ni₂(R^2,2)](ClO₄)₂ (1) crystallizes in the triclinic crystal system, space group P 1, with Z=1, a=8.396(2) Å, b= 10.021(2) Å, c=8.104(2) Å, α=109.56(2)°, β=99.40(2)°, γ=79.89(2)°, V=628.5(3) ų and Z=1. The refinement converges with R=0.0384 and R_w=0.0415 for 2075 reflections with | Fo | > 3[sgrave](| Fo |). In the centrosymmetric [Ni₂(R^2,2)]²⁺, a pair of Ni(II) ions are bridged by two phenolic oxygens with the Ni···Ni separation of 2.801(1) Å. Each Ni assumes a planar configuration with Ni-O bond distances of 1.842(3) and 1.838(3) Å and Ni-N bond distances of 1.814(3) and 1.823(3) Å. In the solid state, 1 is diamagnetic (S₁=S₂=0) whereas [Ni₂(R^2,3)]-(ClO₄)₂ (2) and [Ni₂(R^2,4)](ClO₄)₂ (3) are of a mixed-spin (S₁=0, S₂=1). In DMSO and pyridine all the complexes assume high-spin (S₁=S₂=1). The Ni₂(II,II) complexes are electrochemically reduced in DMSO or pyridine to Ni₂(I,II) and Ni₂(I,I) complexes. The conproportionation constants of the Ni₂(I,II) complexes are determined to be 3.4X10⁴-1.2X10⁵ in DMSO and 1.6X10³-2.6X10⁵ in pyridine. The Ni₂(I,II) and Ni₂(I,I) complexes of 1–3 have been prepared by electrolysis in DMSO. The mixed-valent complexes of 1 and 2 are characterized by an intervalence (IV) transition band at 790 and ～ 700 nm, respectively, and belong to Class II using the classification of Robin and Day. The Ni₂(I,II) complex of 3 shows no IT band (Class I). The Ni₂(I,II) complexes of 1-3 show well-resolved ESR spectra due to the spin-coupled S_T = 1/2 ground-state. The Ni₂(I,I) complexes of 1-3 are all ESR- innocent probably due to the strong antiferromagnetic interaction.     

Endocytosis-like uptake of surface-modified drug nanocarriers into giant unilamellar vesicles

We had previously developed surface-modified poly (D,L-lactide-co-glycolide) (PLGA) nanoparticles (NPs) for use as a cellular drug delivery system. The cellular uptake of PLGA-NPs was mediated predominantly by endocytosis, and this uptake was increased by surface modifications with polymers, such as chitosan (CS) and polysorbate 80 (P80). In the present study, we prepared a cell-sized giant unilamellar vesicle (GUV) that mimics a cell membrane to investigate the interaction between cell membranes and NPs. Endocytosis-like uptake of NPs into a GUV was observed when the NPs were modified with nonionic surfactant P80 probably due to change in viscoelasticity and enhanced fusion activity of the membrane induced by P80. In contrast, unmodified NPs and those modified with CS were not internalized into a GUV. These results suggest that surface properties of PLGA-NPs are an important formulation parameter for their interaction with lipid membranes.     

A 2D layered spin crossover complex constructed by NH...Cl- hydrogen bonds: [FeIIH3LMe]Cl.I3 (H3LMe = tris[2-(((2-methylimidazoyl-4-yl)methylidene)amino)ethyl]amine

A 2D layered spin crossover complex, [FeIIH3L(Me)]Cl.I3, has been synthesized from the reaction of FeIIICl3, a tripod ligand (H3LMe = tris[2-(((2-methylimidazoyl-4-yl)methylidene)amino)ethyl]amine), and NaI in methanol. The compound showed an abrupt spin transition between the HS (S = 2) and LS (S = 0) states at T(1/2) = 110 K without hysteresis. The crystal structures of the HS and LS states were determined at 180 and 90 K. A 2D layered structure is composed of NH...Cl- hydrogen bonds between the Cl- ion and three neighboring imidazole groups of [FeIIH3LMe]2+. The green light irradiation at 5 K induced the LIESST effect, and the thermal relaxation process from the HS to LS state showed a sigmoid curve at T > 55 K.     

NH/pi interaction in a spin-crossover complex [FeII(HLMe)2](BPh4)2.2CH3CN (BPh4-=Tetraphenylborate; HLMe=2-Methylimidazol-4-yl-methylideneamino-2-ethylpyridine)

Three FeII complexes, [Fe(HLR)2](BPh4)2.solvent (R=H, Me, Ph), were synthesized, where BPh4-=tetraphenylborate and HLR=2-substituted-imidazol-4-yl-methylideneamino-2-ethylpyridine. The magnetic susceptibility measurements in 5-300 K revealed that [Fe(HLH)2](BPh4)2.H2O, [Fe(HLMe)2](BPh4)2.2CH3CN, and [Fe(HLPh)2](BPh4)2.CH3CN are low-spin (LS), spin-crossover (SC), and high-spin (HS) FeII complexes, respectively, indicating that the spin state can be effectively tuned by the bulkiness of the substituent. Complex shows a steep SC around 250 K, where it assumes a cyclic structure of {[Fe(HLMe)2]BPh4}2 constructed by four NH/pi bonds between the imidazole group and the phenyl ring of BPh4- in the HS state and a deformed structure with NH/pi bonds and linear CH3CN...HN hydrogen bonds at the terminals in the LS state.