Koji Nakabayashi

A Self‐Assembled Spin Cage

Cationic and anionic cage compounds can show unique molecular recognition capabilities as a consequence of their ionic nature. In contrast, radical cages with unpaired electron spins in their frameworks are seldom prepared and their properties—with the exception of cagelike cluster compounds that have unpaired electrons at metal centers— particularly the interactions with radical guests, are largely unexplored. This is mainly because of difficulties in introducing stable organic radicals at the core of the host frameworks. Here we report the facile self-assembly of a radical cage containing multiple spin centers around a cavity suitable for guest inclusion. We show that verdazyl radical-cored ligand 1 is quantitatively self-assembled into the large M6L4 spin cage 2 upon treatment with a Pd II complex (Scheme 1). Similar to the analogous triazine-cored M6L4

Multifunctionality in Bimetallic LnIII[WV(CN)8]3− (Ln=Gd, Nd) Coordination Helices: Optical Activity, Luminescence, and Magnetic Coupling

Two chiral luminescent derivatives of pyridine bis(oxazoline) (Pybox), (SS/RR)-iPr-Pybox (2,6-bis[4-isopropyl-2-oxazolin-2-yl]pyridine) and (SRSR/RSRS)-Ind-Pybox (2,6-bis[8H-indeno[1,2-d]oxazolin-2-yl]pyridine), have been combined with lanthanide ions (Gd(3+), Nd(3+)) and octacyanotungstate(V) metalloligand to afford a remarkable series of eight bimetallic CN(-)-bridged coordination chains: {[Ln(III)(SS/RR-iPr-Pybox)(dmf)4]3[W(V)(CN)8]3}n ⋅dmf⋅4 H2O (Ln = Gd, 1-SS and 1-RR; Ln = Nd, 2-SS and 2-RR) and {[Ln(III)(SRSR/RSRS-Ind-Pybox)(dmf)4][W(V)(CN)8]}n⋅5 MeCN⋅4 MeOH (Ln = Gd, 3-SRSR and 3-RSRS; Ln = Nd, 4-SRSR and 4-RSRS). These materials display enantiopure structural helicity, which results in strong optical activity in the range 200-450 nm, as confirmed by natural circular dichroism (NCD) spectra and the corresponding UV/Vis absorption spectra. Under irradiation with UV light, the Gd(III)-W(V) chains show dominant ligand-based red phosphorescence, with λmax ≈660 nm for 1-(SS/RR) and 680 nm for 3-(SRSR/RSRS). The Nd(III)-W(V) chains, 2-(SS/RR) and 4-(SRSR/RSRS), exhibit near-infrared luminescence with sharp lines at 986, 1066, and 1340 nm derived from intra-f (4)F3/2 → (4)I9/2,11/2,13/2 transitions of the Nd(III) centers. This emission is realized through efficient ligand-to-metal energy transfer from the Pybox derivative to the lanthanide ion. Due to the presence of paramagnetic lanthanide(III) and [W(V)(CN)8](3-) moieties connected by cyanide bridges, 1-(SS/RR) and 3-(SRSR/RSRS) are ferrimagnetic spin chains originating from antiferromagnetic coupling between Gd(III) (SGd = 7/2) and W(V) (SW = 1/2) centers with J1-(SS) = -0.96(1) cm(-1), J1-(RR) =-0.95(1) cm(-1), J3-(SRSR) = -0.91(1) cm(-1), and J3-(RSRS) =-0.94(1) cm(-1). 2-(SS/RR) and 4-(SRSR/RSRS) display ferromagnetic coupling within their Nd(III)-NC-W(V) linkages.

White Light Emissive DyIII Single‐Molecule Magnets Sensitized by Diamagnetic [CoIII(CN)6]3− Linkers

The self-assembly of Dy(III) -3-hydroxypyridine (3-OHpy) complexes with hexacyanidocobaltate(III) anions in water produces cyanido-bridged {[Dy(III) (3-OHpy)2 (H2 O)4 ] [Co(III) (CN)6 ]}⋅H2 O (1) chains. They reveal a single-molecule magnet (SMM) behavior with a large zero direct current (dc) field energy barrier, ΔE=266(12) cm(-1) (≈385 K), originating from the single-ion property of eight-coordinated Dy(III) of an elongated dodecahedral geometry, which are embedded with diamagnetic [Co(III) (CN)6 ](3-) ions into zig-zag coordination chains. The SMM character is enhanced by the external dc magnetic field, which results in the ΔE of 320(23) cm(-1) (≈460 K) at Hdc =1 kOe, and the opening of a butterfly hysteresis loop below 6 K. Complex 1 exhibits white Dy(III) -based emission realized by energy transfer from Co(III) and 3-OHpy to Dy(III) . Low temperature emission spectra were correlated with SMM property giving the estimation of the zero field ΔE. 1 is a unique example of bifunctional magneto-luminescent material combining white emission and slow magnetic relaxation with a large energy barrier, both controlled by rich structural and electronic interplay between Dy(III) , 3-OHpy, and [Co(III) (CN)6 ](3-) .

FeII Spin‐Crossover Phenomenon in the Pentadecanuclear {Fe9[Re(CN)8]6} Spherical Cluster

The self-assembly of iron(II) ions with rare octacyanidorhenate(V) metalloligands in a methanolic solution results in the formation of a nanometric pentadecanuclear {Fe(II) 9 [Re(V) (CN)8 ]6 (MeOH)24 }⋅10 MeOH (1) molecule with a six-capped body-centered cubic topology. The cluster demonstrates a thermally-induced spin-crossover phase transition at T1/2 =195 K which occurs selectively for a single Fe(II)  ion embedded in the center of a cluster core.

Bis(aminoaryl) Carbon-Bridged Oligo(phenylenevinylene)s Expand the Limits of Electronic Couplings

Carbon-bridged bis(aminoaryl) oligo(para-phenylenevinylene)s have been prepared and their optical, electrochemical, and structural properties analyzed. Their radical cations are class III and class II mixed-valence systems, depending on the molecular size, and they show electronic couplings which are among the largest for the self-exchange reaction of purely organic molecules. In their dication states, the antiferromagnetic coupling is progressively tuned with size from quinoidal closed-shell to open-shell biradicals. The data prove that the electronic coupling in the radical cations and the singlet-triplet gap in the dications show similar small attenuation factors, thus allowing charge/spin transfer over rather large distances.

SHG-active LnIII–[MoI(CN)5(NO)]3− (Ln = Gd, Eu) magnetic coordination chains: a new route towards non-centrosymmetric molecule-based magnets

The rare heteroligand pentacyanidonitrosylmolybdate(I) anion was employed in the construction of d–f bimetallic cyanido-bridged {[LnIII(dmf)6][MoI(CN)5(NO)]} (Ln = Gd, 1; Eu, 2) chains crystallizing in the non-centrosymmetric Pna21 space group. 1 exhibits Gd–Mo antiferromagnetic coupling giving rise to the ferrimagnetic spin chain behaviour with the onset of magnetic ordering below 2 K, and shows high second harmonic generation (SHG) activity with SH susceptibility of 1.2 × 10−10 esu, opening a novel family of non-centrosymmetric molecule-based magnets.

Achieving white light emission and increased magnetic anisotropy by transition metal substitution in functional materials based on dinuclear DyIII(4-pyridone)[MIII(CN)6]3− (M = Co, Rh) molecules

A building block approach has led to the construction of two unique bifunctional magneto-luminescent molecular materials, {[DyIII(4-pyridone)4(H2O)2][MIII(CN)6]}·nH2O (M = Co, n = 2, 1; M = Rh, n = 4, 2), incorporating the cyanido-bridged dinuclear {DyIIICoIII} (1) or {DyIIIRhIII} (2) molecules, that crystallize within the supramolecular network in the attractive non-centrosymmetric Cmc21 space group. Both compounds reveal dual physical properties of colour-tunable photoluminescence and slow relaxation of magnetization. While 1 exhibits multi-coloured photoluminescence ranging from yellow to blue, tuned by the excitation wavelength, 2 additionally reveals nearly white light emission under 336 nm excitation at room temperature. 1 and 2 show 4f-metal-centered strong magnetic anisotropy presenting Single-Molecule Magnet (SMM) behaviour with the large anisotropic energy barriers of 187(6) K for 1, and 214(4) K for 2. We have shown and discussed that the replacement of [CoIII(CN)6]3− by the heavier [RhIII(CN)6]3− analogue in {[DyIII(4-pyridone)4(H2O)2][MIII(CN)6]}·2H2O crystalline materials is an efficient route towards white light emissive solid state matrices composed of Single-Molecule Magnets with enhanced magnetic anisotropy. Such extraordinary photoluminescent molecule-based magnets can become good prerequisites for future application in bifunctional optical and magnetic devices.

In Situ Generation of CoIII–Salen Complexes for Copolymerization of Propylene Oxide and CO2

A simple admixture of Co(II) -salcy complexes with [Cp2 Fe(III) ]PF6 resulted in reproduction of the results with isolated Co(III) -salcy complexes in the copolymerization of epoxide and carbon dioxide. By using this in situ-generated active species with bis(triphenylphosphoranilydene)ammonium 2,4-dinitrophenolate, a para-methoxy-substituted Co-salcy complex was proven to be more active than the parent tert-butyl-substituted system. In contrast, the Co(II) -salcy complex substituted with the more strongly electron-donating NMe2 group did not show any activity for this copolymerization.

High thermal durability of a layered Cs4CoII[WV(CN)8]Cl3 framework: crystallographic and 133Cs NMR spectroscopic studies

Temperature-variable single-crystal synchrotron X-ray diffraction and 133Cs NMR studies were performed for a cyanido-bridged layered metamagnet, Cs4CoII[WV(CN)8]Cl3 (1), to elucidate the origin of its unusually high thermal durability up to ca. 523 K (250 °C). 1 reveals a layered structure composed of negatively charged two-dimensional cyanido-bridged Co–W layers ({CoII[WV(CN)8]Cl3}4−) and cesium ions between and within the layers, where there is a lack of both non-coordinated and coordinated solvent molecules that is an important and characteristic feature of the crystal structure. The cesium ions are surrounded by chlorides and cyanides of the coordination layers, and some Cs+⋯Cl−, Cs+⋯N, and Cs+⋯C distances are shorter than the estimated sums of an ionic radius of Cs+ and ionic or van der Waals radii of Cl−/CN−. These short distances suggest strong interactions between Cs+ and Cl−/CN−, which stabilize the crystal structure by connecting the layers. The temperature-dependent single-crystal structural analyses show that there is no significant structural change upon heating up to 473 K, and indicate that the short distances between Cs+ and Cl−/CN− still remain. Thus, the high thermal durability of 1 is due to not only the absence of solvent molecules but also the existence of strong Cs+⋯Cl− and Cs+⋯−NC interactions. The 133Cs NMR spectrum shows four peaks assignable to the four independent Cs+ ions in the crystal structure. The observed peaks were located in high ppm owing to the hyperfine interactions between the nuclear spin of Cs and electron spins from the magnetic centers CoII and WV. As temperature increased, the peaks moved to low ppm, and the shifts of the peaks are expressed by the Curie–Weiss law indicating no large structural changes around Cs+ ions, that is, the Cs+ ions are fixed at the same positions. This proves the presence of strong interactions involving Cs+ and terminal ligands of cyanido-bridged layers of 1 being responsible for its high thermal stability.

catena-Poly[[[tetra­kis­(cyanido-κC)tungstate(IV)]-di-μ-cyanido-κ4 C:N-bis­[diaqua­(2,2′-bipyridyl-κ2 N,N′)manganese(II)]-di-μ-cyanido-κ4 N:C] hexa­hydrate]

The polymeric title compound, {[MnII 2WIV(CN)8(C10H8N2)2(H2O)4]·6H2O}n, has a one-dimensional cyanide-bridged MnII–WIV bimetallic assembly. The coordination geometry of the WIV atom is eight-coordinate square-antiprismatic and that of each of the MnII atoms is six-coordinate distorted octahedral. Two pairs of CN ligands of W(CN)8 are bridged to two MnII atoms, the remaining CN ligands being terminal. Each MnII atom is additionally coordinated by a bidentate 2,2′-bipyridyl ligand and two water molecules. The crystal structure is stabilized by O—H⋯O and O—H⋯N hydrogen bonds.