ja7b07803_si_003.pdf (9.85 MB)
Cobalt Porphyrin–Thiazyl Radical Coordination Polymers: Toward Metal–Organic Electronics
journal contribution
posted on 2017-09-19, 00:00 authored by Delia A. Haynes, Laura J. van Laeren, Orde Q. MunroHerein we delineate an unusual one-dimensional
coordination polymer
(CP), 3, prepared from S = 1/2 Co(TPP), 1 (TPP = 5,10,15,20-tetraphenylporphyrin dianion), and S = 1/2 4-(4′-pyridyl)-1,2,3,5-dithiadiazolyl (py-DTDA)
radical, 2. The atypically long S–S distance for
CP 3 (2.12 Å) reflects fractional electron transfer
from the formally Co(II) ion into the antibonding π-SOMO of
the metal-bound py-DTDA bridging ligand. The bonding in solid CP 3 involves noninteger redox states in a resonance hybrid repeat
unit best formulated as [Co(TPP)]0.5+ hemication (Co2.5+) bound to a dithiadiazolide hemianion (py-DTDA0.5–). DFT calculations confirm the metal to ligand charge transfer (MLCT)
character of the low-lying electronic states (641, 732, and 735 nm)
observed for CP 3 and show that oligomer chains of length
≥14 repeat units tend toward a band structure with a limiting
band gap energy of 0.669(6) eV. In dichloromethane, the reaction between
radicals 1 and 2 involves coordination of
the Co(II) ion by a py-DTDA ring sulfur atom, orbitally favored spin-pairing,
and the formation of the thermodynamically favored diamagnetic five-coordinate
S-bound adduct, Co(TPP)(S-py-DTDA), 3a. Polymerization and crystallization of 3a affords diamagnetic
CP 3. Dissolution of CP 3 in DMSO favors
Co–S bond heterolysis, yielding the diamagnetic six-coordinate
purple N-bound CoIII(TPP)(N-py-DTDA–)(OSMe2) complex (λmax, 436 nm). However, monomerization of CP 3 in dry 1,2-dichloroethane
affords bright green diamagnetic CoIII(TPP)(N-py-DTDA–), 3b, with multiple MLCT
bands in the 800–1100 nm NIR region and a red-shifted Soret
band (λmax, 443 nm). Implications for the use of
CP 3 in electronic devices are discussed based on its
density of states.