Cucos, Paula Tuna, Floriana Sorace, Lorenzo Matei, Iulia Maxim, Catalin Shova, Sergiu Gheorghe, Ruxandra Caneschi, Andrea Hillebrand, Mihaela Andruh, Marius Magnetic and Luminescent Binuclear Double-Stranded Helicates Three new binuclear helicates, [M<sub>2</sub>L<sub>2</sub>]·3DMF (M = Co­(II), <b>1</b>, Zn­(II), <b>3</b>) and [Cu<sub>2</sub>L<sub>2</sub>]·DMF·0.4H<sub>2</sub>O (<b>2</b>), have been assembled using the helicand H<sub>2</sub>L that results from the 2:1 condensation reaction between <i>o</i>-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. temperature dependence;55 K;relaxation rate;Dynamic susceptibility measurements evidence;metal ions;helicate;Orbach mechanism;EPR spectroscopy;axis type anisotropy;dc field;Zn;fluorescence quantum yields;Co;exhibits fluorescence emission;tetrahedral geometry;M 2L;center;cobalt ions;helicand H 2L 2014-07-21
    https://acs.figshare.com/articles/journal_contribution/Magnetic_and_Luminescent_Binuclear_Double_Stranded_Helicates/2272801
10.1021/ic501051q.s004