Magnetic and Luminescent Binuclear Double-Stranded Helicates

Abstract

Three new binuclear helicates, [M2L2]·3DMF (M = Co(II), 1, Zn(II), 3) and [Cu2L2]·DMF·0.4H2O (2), have been assembled using the helicand H2L that results from the 2:1 condensation reaction between o-vanillin and 4,4'-diaminodiphenyl ether. The metal ions within the binuclear helicates are tetracoordinated with a distorted tetrahedral geometry. Direct current magnetic characterization and EPR spectroscopy of the Co(II) derivative point to an easy axis type anisotropy for both Co(II) centers, with a separation of at least 55 K between the two doublets. Dynamic susceptibility measurements evidence slow relaxation of the magnetization in an applied dc field. Since the distance between the cobalt ions is quite large (11.59 Å), this is attributed in a first instance to the intrinsic properties of each Co(II) center (single-ion magnet behavior). However, the temperature dependence of the relaxation rate and the absence of slow dynamics in the Zn(II)-doped sample suggest that neither the simple Orbach mechanism nor Raman or direct processes can account for the relaxation, and collective phenomena have to be invoked for the observed behavior. Finally, due to the rigidization of the two organic ligands upon coordination, the pure zinc derivative exhibits fluorescence emission in solution, which was analyzed in terms of fluorescence quantum yields and lifetimes.

Organic synthesis by Twin Screw Extrusion (TSE): continuous, scalable and solvent-free

“…The solution reaction involves refluxing 4,4'-oxydianiline with 2 equivalents of ortho-vanillin in methanol for several hours. 25 The imine formed within 30 minutes of ball milling at 25 Hz, without the addition of solvent. The reaction was subsequently scaled from 0.5 g per batch (by ball milling) to 0.03 kghr -1 via twin screw extrusion, producing the desired Schiff base as a bright orange powder ( Figure 17).…”

Evidence of Slow Magnetic Relaxation in Co(AcO)2(py)2(H2O)2

“…The double well model holds up in the case of monometallic cobalt(II) SMMs with negative D values [9,[11][12][13][14][15][16][17][18][19], but the observation of similar behaviour in monometallic cobalt(II) complexes with positive D values [20][21][22] suggests that the picture is more complex. Indeed, slow relaxation in positive-D compounds is a phenomenon that is not yet fully understood-although attempts have been made to explain it [23,24].…”

Self‐assembly of Dinuclear Double‐stranded Copper(II) Helicates with 3‐Ethoxy‐2‐hydroxyphenyl Substituted Diimines. Synthesis, Molecular Structure, and Host‐guest Recognition of H2O

“…The isolated complexes are either homodinuclear {Co II , Cu II , Zn II with N 2 O 2 donor set} [15,16] or heterotetranuclear {N 2 O 2 : Cu II / O 4 : Gd III } double-stranded helicates. [17,18] As part of our ongoing studies in this research field we have synthesized the 3-ethoxy-2-hydroxyphenyl-substituted diimines H 2 L 1 and H 2 L 2 having diphenyl methane or diphenyl sulfide spacer units, respectively (Scheme 1).…”

“…[19,20] It is interesting to note, that upon cooling of the solid ligand a color change is observed indicating a thermochromism between both tautomers as observed previously for similar ligands. [20,21] [5,[14][15][16]18] However, the Cu···Cu separation is with 11.53 Å significantly shorter as in the structure related helicates (the data are given in Table S11, Supporting Information). The helical twist of the ligands around the two central Cu II atoms, defined by the dihedral angle Cu(1)-N(1)-N(2)-Cu (2), is 169.4°.…”