Sumio Kaizaki

Crystal structures of cobalt(II), nickel(II) and zinc(II) dichloro complexes bearing 2-pyridyl-substituted nitronyl nitroxide (NIT2py)

The X-ray analysis of Co(II), Ni(II) and Zn(II) dichloro complexes containing 2-(2-pyridyl)-4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide (NIT2py) demonstrated that the Co(II) complex containing two dichloromethane solvate molecules, [CoCl2(NIT2py)2]·2CH2Cl2 (1), crystallizes in a space group P21/c isomorphous to the corresponding Mn(II), Ni(II) (2) and Cu(II) complexes, and that the molecular structure of the complex having Ci symmetry in 1 is isostructural to the above Mn(II), Ni(II) and Cu(II) complexes. A new Ni(II) complex having only one dichloromethane solvate molecule, [NiCl2(NIT2py)2]·CH2Cl2 (2′), could be crystallized from a mixture of dichloromethane, methanol and n-heptane. The (OC-6-12)-[trans(Cl)-trans(py)] geometrical structure of the Ni(II) complex in 2′ is identical to that in 2, but the puckered six-membered chelate rings formed via pyridyl-N and nitroxide-O atoms of NIT2py take the different conformations; i.e. the molecular symmetry is C2 (racemate) with the λ, λ or δ, δ conformations in 2′ and Ci (meso) with the δ, λ conformations in 2. In the case of Zn(II), a reaction of ZnCl2 with NIT2py afforded purple crystals consisting of octahedral bis(NIT2py) and tetrahedral mono(NIT2py) complexes with hydration: [ZnCl2(NIT2py)2]·2[ZnCl2(NIT2py)]·2/3H2O (3). The geometrical structure of the octahedral Zn(II) complex in 3 was found to be (OC-6-22)-[cis(Cl)-trans(py)].

Syntheses, structures, magnetic and spectroscopic properties of bis(pentane-2,4-dionato)chromium(III) complexes incorporating 3- or 4-pyridyl-substituted nitronyl and imino nitroxides

Preparation and characterization by X-ray analysis and 2H NMR spectra have been described for twelve chromium(III)–nitroxide complexes of cis-[Cr(acac)2Cl(L)] and cis- and trans-[Cr(acac)2(L)2]PF6 with 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-pyridyl)imidazolin-1-oxyl 3-oxide (NIT3py or NIT4py) and 4,4,5,5-tetramethyl-2-(3- or 4-pyridyl)imidazolin-1-oxyl (IM3py or IM4py). An intramolecular magnetic interaction between CrIII and 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 CrIII dπ orbitals. 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-pyridyl)imidazolin-1-oxyl 3-oxide] and IM2py [4,4,5,5-tetramethyl-2-(2-pyridyl)imidazolin-1-oxyl] complexes. This may be accounted for by the difference in the mechanism of magnetic interactions; spin-polarization mechanism and exchange mechanism, respectively.

Synthesis, spectroscopic and magnetic properties of lanthanide(III) complexes with a chelated imino nitroxide radical

The treatment of [Ln(hfac)3(H2O)2] (Ln(III) = Y, Nd–Lu) with IM-2py (2-(2-pyridyl)-4,4,5,5-tetramethyl-1H-imidazolyl-1-oxyl) readily gave a series of novel rare earth or lanthanide radical complexes [Ln(hfac)3(IM-2py)]. The molecular structures of the Sm, Gd, Dy, Er and Yb complexes have been determined to be bicapped trigonal prismatic (TPRS) by X-ray diffraction. The magnetic susceptibility data for [Gd(hfac)3(IM-2py)] show that the Gd–IM-2py interaction is weakly antiferromagnetic with an exchange coupling constant J n= n−3.00 cm−1 in contrast to the ferromagnetic interaction in the Gd(III)–nitronyl nitroxide complexes. The n–π* transition of IM-2py is found to shift to lower frequency associated with intensity enhancement and vibronic structure. The luminescence measurement of the Eu(III) and Tb(III) ncomplexes demonstrated energy transfers for IM-2py (SOMO π*) → Ln(III) (4f) as a result of emission quenching; this depends on the energy gap between the excited levels in Ln(III) and IM-2py. These results reveal that the metal–radical interactions are very weak magnetically but are relatively strong with respect to energy transfer.

Crystal structures, magnetic and spectroscopic properties of manganese(II), cobalt(II), nickel(II) and zinc(II) dichloro complexes bearing two 2-pyridyl-substituted imino nitroxides

Four new complexes of formula [MCl2(IM2py)2], where Mxa0=xa0Mn(II), Co(II), Ni(II) or Zn(II); IM2pyxa0=xa04,4,5,5-tetramethyl-2-(2-pyridyl)-imidazolin-1-oxyl, have been prepared, and examined from viewpoints of the crystal structures, magnetic and spectroscopic properties. All the complexes crystallize in an isomorphous space group C2/c with Zxa0=xa04, and exist as discrete mononuclear molecules with OC-6-22 [cis(Cl)-trans(py)] geometrical structure in the crystal. In the zinc(II) complex a moderate intramolecular IM2py–IM2py antiferromagnetic interaction (2J′xa0=xa0−19.1(1) cm−1) is estimated by the magnetic susceptibility measurement. The magnetic interactions between Mn(II) and IM2py are found to be antiferromagnetic, Jxa0=xa0−23.8(2) cm−1. Ferromagnetic interactions of the complexes of Ni(II) and Co(II) are inferred from the magnetic susceptibility. These magnetic properties are substantiated by the variable temperature UV-vis-NIR spectra of which the intensities increase for Mn(II) or decrease for Ni(II) and Co(II) with decreasing temperature for the spin-forbidden d–d transition and/or the metal(II) dσ to IM2py SOMO π* CT transition.

Synthesis and Properties of Lanthanide(III) Complexes Containing Pyridine-Substituted Imino Nitroxide Radical

Some lanthanide(III) complexes containing three types of a chelated n-methylpyridine-substituted imino nitroxide radical IM n Me2py( n =4,5,6) were synthesized with a small size of the multi-spin system. X-ray structural analysis of [Gd(hfac) 3 (IM6Me2py)], [Dy(hfac) 3 (IM4Me2py)] demonstrated that they are rigidly eight-coordinted with one IM n Me2py and three hfac ligands. Magnetic susceptibility measurements of the Gd(III) complexes indicate that the antiferromagnetic interaction between Gd(III) and imino nitroxide radical is different from the other lanthanide complexes containing nitronyl radicals. lanthanide imino nitroxide radical crystal structures magnetic interaction

Proton-transfer-mediated crystal engineering using 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile with 4,4′-bipyridine

The crystal structure of a salt [Hbpy][Htdpd] n(1) n(bpy = 4,4′-bipyridine, H2tdpd = 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile) is reported; the supramolecular structure is rationally designed via hydrogen bonding interactions.

Laser emission in 4f-4f transitions of some Nd(III) complexes

The emission spectra of the [(acac) 2 Cr(ox)Nd(HBpz 3 ) 2 ](Cr(ox)Nd) complex corresponding to both the 4f-4f emission of the Nd(III) at room temperature and the 2 E emission of the Cr(III) chromophore at low temperature were observed. Both the complexes [(HBpz 3 ) 2 Nd(ox)Nd(HBpz 3 ) 2 ] (Nd(ox)Nd) and [Nd 2 ( w -pba) 4 (HBpz 3 ) 2 ] exhibit several 4f-4f emission bands in the NIR region. laser emission 3d-4f complex 4f-4f complex Nd(III) complexes

Triple Hydrogen Bond Directed Crystal Engineering of Metal Assembled Complexes: The Effect of a Novel Organic-Inorganic Module on Supramolecular Structure

The new manganese(II) and zinc(II) triply hydrogen-bonded complexes [Hmel] 2 [M(tdpd) 2 (OH 2 ) 2 ]2H 2 O (M = Mn 2+ ( 2 ); Hmel + = melaminium cation; H 2 tdpd = 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile) have been synthesized and characterized. These complexes are isostructural as revealed by their single crystal structure analyses. Both the compounds are composed of triply hydrogen-bounded module of the AAA L DDD system. triple hydrogen bonding manganese zinc

Tricarbonyl[1,1,1-tris(dimethylphosphinomethyl)ethane]chromium(0), -molybdenum(0) and -tungsten(0) complexes

The structures of chromium(0)-, molybdenum(0)- and tungsten(0)-tricarbonyl complexes containing the tripodal tridentate phosphine ligand 1,1,1-tris(dimethylphosphinomethyl)ethane (tdmme) (systematic name: {2-[(dimethylphosphino)methyl]-2-methyl-1,3-propane-diyl}bis(dimethylphosphine)), were determined by X-ray diffraction studies. The M-C (M = Cr, Mo and W) bond lengths in the complexes, [M(C 11 H 27 P 3 )(CO) 3 ], are noticeably shorter than those in the corresponding hexacarbonyl complexes owing to the trans influence of tdmme being weaker than that of CO. The Mo-P bond lengths in the tdmme complex are slightly shorter than those in the analogous 1,1,1-tris(diphenylphosphinomethyl)ethane and 1,5,9-tris(isopropyl)-1,5,9-triphosphacyclododecane complexes, indicating the smaller steric requirement of tdmme.

A nitronyl nitroxide complex of nickel(II) with nitrate as a ligand.

The complex cation in [4,5-dihydro-4,4,5,5-tetramethyl-2-(2-pyridyl-kappa N)imidazol-1-oxyl 3-oxide-kappa O(3)](nitrato-kappa(2)O,O)(N,N,N,N-tetramethyl-1,2-ethanediamine-kappa(2)N,N)nickel(II) hexafluorophosphate dichloromethane solvate, [Ni(NO(3))(C(6)H(16)N(2))(C(12)H(16)N(3)O(2))]PF(6) x CH(2)Cl(2), is the first example of a nitronyl nitroxide complex of a transition metal ion having d electrons in which nitrate is coordinated as a bidentate ligand. Owing to the smaller steric requirement of NO(3)(-), the Ni-O(nitroxide) bond length [2.014 (2) A] is remarkably shorter than that in the corresponding beta-diketonate complexes [2.052 (4)-2.056 (2) A].