Singly and Triply Linked Magnetic Porphyrin Lanthanide Arrays

The introduction of paramagnetic metal centers into a conjugated pi-system is a promising approach toward engineering spintronic materials. Here,we report an investigation of two types of spin-bearing dysprosium(III) andgadolinium(III) porphyrin dimers: singlymeso-meso-linked dimers with twistedconformations and planar edge-fused beta,meso,beta-linked tapes. The rare-earth spincenters sit out of the plane of the porphyrin, so that the singly linked dimers arechiral, and their enantiomers can be resolved, whereas the edge-fused tapecomplexes can be separated intosynandantistereoisomers. We compare thecrystal structures, UV-vis-NIR absorption spectra, electrochemistry, EPRspectroscopy, and magnetic behavior of these complexes. Low-temperatureSQUID magnetometry measurements reveal intramolecular antiferromagnetic exchange coupling between the GdIIIcenters in theedge-fused dimers (synisomer:J=-51 +/- 2 MHz;antiisomer:J=-19 +/- 3 MHz), whereas no exchange coupling is detected in thesingly linked twisted complex. The phase-memory times,Tm, are in the range of 8-10 mu s at 3 K, which is long enough to testquantum computational schemes using microwave pulses. Both thesynandantiDy2edge-fused tapes exhibit single-moleculemagnetic hysteresis cycles at temperatures below 0.5 K with slow magnetization dynamics.