Influence of Tetraazamacrocyclic Ligands on the Nitric Oxide Reactivity of their Cobalt(II) Complexes

Abstract

The reactions of cobalt(II) complexes of tetraazamacrocyclic tropocoronand (TC) ligands with nitric oxide (NO) were investigated. When [Co(TC-5,5)] was allowed to react with NO(g), the {CoNO}(8) mononitrosyl [Co(NO)(TC-5,5)] was isolated and structurally characterized. In contrast, a {Co(NO)(2)}(10) species formed when [Co(TC-6,6)] was exposed to NO(g), and the nitrito [Co(NO(2))(TC-6,6)] complex was structurally and spectroscopically characterized from the reaction mixture. The {Co(NO)(2)}(10) species was assigned as the bis(cobalt dinitrosyl) complex [Co(2)(NO)(4)(TC-6,6)] by spectroscopic comparison with independently synthesized and characterized material. These results provide the first evidence for the influence of tropocoronand ring size on the nitric oxide reactivity of the cobalt(II) complexes.

Singlet–Triplet Gaps of Cobalt Nitrosyls: Insights from Tropocoronand Complexes

“…The calculations also revealed a decreasing singlet-triplet gap and low-energy triplet states as the coordination geometry changed from the nearly SQP TC-3,3 complex to the TBP TC [5][6]6 complexes. Thermally accessible triplet states are a distinct possibility for 6,6)(NO)], which would explain its apparent instability.…”

“…The hybrid functional B3LYP overestimates the Co-N distance by up to 20 0.06 Å, whereas the pure functionals PW91 and OLYP underestimate this distance by up to 0.07 Å. For 5) (NO)], all three functionals appear to overestimate the CoNO angle by about 10°. Although these errors are slightly on the high side, they are still within acceptable limits, given that 25 we have not made any attempt to model the solid-state environments of the molecules in question.…”

Recent advances in multinuclear metal nitrosyl complexes

“…Lippard’s group also investigated reactions between cobalt(II) complexes containing tetraazamacrocyclic tropocoronand (TC) ligands and nitric oxide and reported that a bis(cobalt dinitrosyl) complex [Co 2 (NO) 4 (TC-6,6)], 23 , was formed when [Co(TC-6,6)] was exposed to gaseous NO [109]. The end product depended on the ring size: in the same reaction with [Co(TC-5,5)], only the mononitrosyl complex [Co(NO)(TC-5,5)] was isolated.…”

The Preparation, Structural Characteristics, and Physical Chemical Properties of Metal-Nitrosyl Complexes

“…Recent work is also focusing on compounds that are harder to synthesize, like those involving rare or radioactive metals [58, 59], or the isolation of unstable products with metals that usually do not form nitrosyls such as copper [60] while other molecules are synthesized for their specific abilities, such as hydrogen bonding [61]. …”