Electronic structure and exchange interactions in cobalt-phthalocyanine chains

The magnetic properties and electronic structure of cobalt phthalocyanine (CoPc, spin-1/2) molecular chains have been studied using density functional theory with a hybrid exchange functional, over a wide range of chain geometries. Our theoretical results for the exchange interactions in the known phases alpha-CoPc (J/k(B) similar to 85 K) and beta-CoPc (J/k(B) similar to 2 K) are in quantitative agreement with recent magnetic measurements; we also find the computed exchange interaction agrees qualitatively with recentmeasurements by inelastic tunneling spectroscopy on thin films. The computed exchange interactions are much larger than those in copper phthalocyanine (CuPc), and are predicted to rise to a maximum of J/k(B) similar to 400Kwhen the molecules are face-on. The dominant exchange mechanism is expected to be superexchange arising from the direct hopping between d(z2) orbitals.