Stars and stripes: hexatopic tris(3,2':6',3''-terpyridine) ligands that unexpectedly form one-dimensional coordination polymers

The hexatopic ligands 1,3,5-tris(4,2':6',4''-terpyridin-4'-yl)benzene (1), 1,3,5-tris(3,2':6',3''-terpyridin-4'-yl)benzene (2), 1,3,5-tris{4-(4,2':6',4''-terpyridin-4'-yl)phenyl}benzene (3), 1,3,5-tris{4-(3,2':6',3''-terpyridin-4'-yl)phenyl}benzene (4) and 1,3,5-trimethyl-2,4,6-tris{4-(3,2':6',3''-terpyridin-4'-yl)phenyl}benzene (5) have been prepared and characterized. The single crystal structure of 1·1.75DMF was determined; 1 exhibits a propeller-shaped geometry with each of the three 4,2':6',4''-tpy domains being crystallographically independent. Packing of molecules of 1 is dominated by face-to-face π-stacking interactions which is consistent with the low solubility of 1 in common organic solvents. Reaction of 5 with [Cu(hfacac)2]·H2O (Hhfacac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) under conditions of crystal growth by layering resulted in the formation of [Cu3(hfacac)6(5)] n ·2.8nC7H8·0.4nCHCl3. Single-crystal X-ray diffraction reveals an unusual 1D-coordination polymer consisting of a series of alternating single and double loops. Each of the three crystallographically independent Cu atoms is octahedrally sited with cis-arrangements two N-donors from two different ligands 1 and, therefore, cis-arrangements of coordinated [hfacac]- ligands; this observation is unusual among compounds in the Cambridge Structural Database containing {Cu(hfacac)2N2} coordination units in which the two N-donors are in a non-chelating ligand.

Electrochromic Os-based metallo-supramolecular polymers: electronic state tracking by in situ XAFS, IR, and impedance spectroscopies

In this study, the electronic states of Os-based metallo-supramolecular polymers (poly(OsL)²⁺) during electrochromism were tracked by in situ X-ray absorption fine structure (XAFS), infrared (IR), and impedance spectroscopies. The XAFS spectra suggested electronic charge migration in the polymer, and the in situ spectra revealed reversible changes caused by electrochemical redox reactions. The IR spectra of the polymers showed an IVCT band, and we also confirmed the reversible changes by applying a voltage to the redox cell. During the impedance measurements, we found a drastic decrease in the charge transfer resistance (R_CT) of the polymer films near the electrochemical redox potential.

In this study, the electronic states of Os-based metallo-supramolecular polymers (poly(OsL)²⁺) during electrochromism were tracked by in situ X-ray absorption fine structure (XAFS), infrared (IR), and impedance spectroscopies.

Ni(II)-Based Metallosupramolecular Polymer with Carboxylic Acid Groups: A Stable Platform for Smooth Imidazole Loading and the Anhydrous Proton Channel Formation

The Ni(II)-based metallosupramolecular polymer with carboxylic acid groups (polyNi) was synthesized via a 1:1 complexation of Ni(II) salt with (4,4'-(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(pyridine-2,6-dicarboxylic acid) for the first time. The divalent state of Ni(II) in the polymer was confirmed by the X-ray absorption fine structure analysis. Smooth loading of imidazole molecules into polyNi proceeded with the help of the carboxylic acid groups to form the imidazole-loaded polyNi (polyNi-Im). Thermogravimetric analysis of polyNi-Im revealed that approximately three imidazole molecules were incorporated per repeating unit of polyNi. The Fourier transform infrared spectrum of polyNi-Im showed a new peak at 3219 cm-1, which shows an ∼73 cm-1 enhancement to -N-H of pristine imidazole. The peak suggests the formation of an imidazolium cation in the polymer. Powder X-ray diffraction indicated no degradation of the polymer structure during the imidazole loading because the diffraction pattern of polyNi-Im was almost the same as that of polyNi except for the presence of peaks corresponding to the imidazole molecules. Interestingly, the scanning electron microscopy measurement showed a large morphological change to uniform spherical particles by loading imidazole to the polymer. PolyNi-Im exhibited good proton conductivity (1.05 × 10-2 mS/cm) at a high temperature (120 °C), which is around 7 orders of magnitude higher than that of pristine polyNi because of the proton conduction pathway formation along the polymer chains by the incorporated imidazole molecules.

Reversible four-color electrochromism triggered by the electrochemical multi-step redox of Cr-based metallo-supramolecular polymers

Four color electrochromism (yellow, magenta, blue, and navy) has been achieved in Cr(iii)-based metallo-supramolecular polymers (polyCr), which were synthesized by 1 : 1 complexation of Cr ions and 1,4-di[[2,2′:6′,2′′-terpyridin]-4′-yl]benzene (L).

Modulation of a coordination structure in a europium(iii)-based metallo-supramolecular polymer for high proton conduction

Developing high proton conducting solid materials is significant in the field of fuel cells. A europium(iii)-based metallo-supramolecular polymer with uncoordinated carboxylic acids (PolyEu-H) was successfully synthesized by modifying the synthesis conditions. The proton conductivity was enhanced with increasing the relative humidity (RH) from 30 to 95% RH. PolyEu-H showed about 10⁴ times higher proton conductivity than the polymer with coordinated carboxylic acids (PolyEu) and about 400 times higher than the polymer without carboxylic acids (PolyEu-2). The proton conductivity of PolyEu-H reached 4.45 × 10⁻² S cm⁻¹ at 95% RH and 25 °C and 5.6 × 10⁻² S cm⁻¹ at 75 °C. The activation energy, E_a was ultralow (0.04 eV), which indicates proton conduction based on the Grotthuss mechanism. The results indicate that efficient proton conduction occurs through proton channels formed by moisture in PolyEu-H.

Developing high proton conducting solid materials is significant in the field of fuel cells. We firstly synthesized europium(iii)-based metallo-supramolecular polymer with uncoordinated carboxylic acids (PolyEu-H), for high proton conduction.

Proton Conductive Nanosheets Formed by Alignment of Metallo-Supramolecular Polymers

Linear Fe(II)-based metallo-supramolecular polymer chains were precisely aligned by the simple replacement of the counteranion with an N,N'-bis(4-benzosulfonic acid)perylene-3,4,9,10-tetracarboxylbisimide (PSA) dianion, which linked the polymer chains strongly. A parallel alignment of the polymer chains promoted by the PSA dianions yielded nanosheets formation. The nanosheets' structure was analyzed with FESEM, HRTEM, UV-vis, and XRD in detail. The nanosheets showed more than 5 times higher proton conductivity than the original polymer due to the smooth ionic conduction through the aligned polymer chains. The complex impedance plot with two semicircles also suggested the presence of grain boundaries in the polymer nanosheets.

Thermally resistant unsaturated polyester resin with low dielectric loss based on special benzyl alcohol terminated hyperbranched polysiloxane for producing high efficiency motors using vacuum pressure impregnation technique

New hyperbranched polysiloxane/unsaturated polyester resins for fabricating high efficient motors through vacuum pressure impregnation technique were developed.