Synthesis, crystal structures, and magnetic properties of nitroxide radical-coordinated manganese(II) and cobalt(II) complexes

Coordination complexes constructed from the nitronyl nitroxide radical NIT-Pyra-3-Isobu and MII(hfac)2(H2O)2 as building blocks (NIT-Pyra-3-Isobu = 2-(3-isobutyl-pyrazole)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, hfac = hexafluoroacetylacetonato, and M = Mn or Co) are successfully synthesized. The crystal structures of the coordination compounds reveal the usefulness of the functionalized radical in providing discrete or extended architectures. Single-crystal X-ray diffraction analyses indicated that the ligand is coordinated through the oxygen atom of NO• and the N atom of the pyrazole linkage to the metal, and the metals adopt an octahedral geometry leading to one-dimensional zig-zag chain systems. The magnetic behavior of the manganese and cobalt shows overall antiferromagnetic interactions between the metal center and the organic radical.

Chemoenzymatic Synthesis of Branched Glycopolymer Brushes as the Artificial Glycocalyx for Lectin Specific Binding

The artificial glycocalyx fabricated by carbohydrates is of interest because it provides a platform to simulate the cell membranes that widely exist in the nature, and thus enable extensive applications to be implantable in bioengineering. Here, we present a green strategy combining two polymerization techniques, surface-initiated atom transfer radical polymerization (SI-ATRP) and enzyme-catalyzed elongation of polysaccharide, for fabricating densely packed branched glycopolymer brushes on the gold surface as the artificial glycocalyx. In this strategy, SI-ATRP is first performed to graft a linear polymer chain for anchoring maltose, which can be used as an enzyme acceptor for dextransucrase (DSase). Under DSase, a branched polysaccharide is efficiently formed through elongation of a sucrose substrate. Undoubtedly, enzymatic transglycosylation has unique advantages, such as being green, regio-, and stereo-selective, etc. The process of DSase-catalyzed polysaccharide is well monitored by a quartz crystal microbalance, and the grafting density of the glycopolymer brushes is estimated to be 0.7 chain nm^-2 with 23.0 nm dry thickness. The polysaccharide brushes display a branched structure consisting of α-d-glucose residues with 5% of α-1,3-linked shorter chain branches, and the branched structure is well characterized by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, Fourier transform infrared/mirror reflection, water contact angle analysis, and atomic force microscopy. Compared with the linear maltose-anchored brushes, the branched glycopolymer analog prepared here shows high specific binding capacity of concanavalin A recognition, which should be of use in biomedical application.

Heterometallic grids: synthetic strategies and recent advances

Supramolecular metallogrid complexes are metalloclusters involving metal ions in planar array arrangements and organic ligands in perpendicular arrangements at each corner of the metal sites. Such essentially metal ion arrays have attracted great attention in the last three decades owing to their variety of interesting optical, electronic and magnetic properties. Among them, metallogrids containing more than one type of metal, that is heterometallic grids, are rare but have more potential to engineer a higher level functionality into one molecule. However, until now, only dozens of heterometallic grids have been reported without any specific review. Herein, we aim to give an overview of the assembly strategies, the physicochemical properties, and finally some perspectives on the future development of heterometallic grids.

Pre-programmed self-assembly of polynuclear clusters

This perspective reviews our recent efforts towards the self-assembly of polynuclear clusters with ditopic and tritopic multidentate ligands HL1 (2-phenyl-4,5-bis{6-(3,5-dimethylpyrazol-1-yl)pyrid-2-yl}-1H-imidazole) and H2L2 (2,6-bis-[5-(2-pyridinyl)-1H-pyrazole-3-yl]pyridine), both of which are planar and rigid molecules. HL1 was found to be an excellent support for tetranuclear [Fe4] complexes, [FeII4(L1)4](BF4)4 ([FeII4]) and [FeIII2FeII2(L1)4](BF4)6 ([FeIII2FeII2]). The homovalent system was found to exhibit multistep spin crossover (SCO), while the mixed-valence [FeIII2FeII2] complex shows wavelength-dependent tuneable light-induced excited spin state trapping (LIESST). For H2L2, a variety of polynuclear complexes were obtained through complexation with different transition metal ions, allowing the isolation of rings, grids, and helix structures. The rigidity of the ligand, difference in its coordination sites, and affinity for different metal ions dictates its coordination behaviour. In this paper, we summarise these ligand pre-programmed self-assembled clusters and their diverse physical properties.

Magnetic relaxation in [Ln(hfac)4]− anions with [Cu(hfac)-radical]nn+ cation chains as counterions

Two novel 3d–4f compounds involving [Ln(hfac)₄]⁻ anions and {[Cu-radical]⁺}_n cation chains are presented. The Dy derivative exhibits slow magnetization relaxation.

A stable open-shell redox active ditopic ligand

Herein we describe the synthesis, structure and electronic properties of an unusual redox-active ditopic ligand with a stable open-shell configuration. This stable phenoxyl radical features intense and very low energy electronic transitions in the near infrared (NIR) part of the spectrum and is structurally set up to strongly spin couple coordinated transition metal ions in [2 × 2] grid-type structures.