Mononuclear (nitrido)iron(V) and (oxo)iron(IV) complexes via photolysis of [(cyclam-acetato)Fe-III(N-3)](+) and ozonolysis of [(cyclam-acetato)Fe-III(O3SCF3)](+) in water/acetone mixtures

摘要

Reaction of the monoanionic, pentacoordinate ligand lithium 1,4,8,11-tetraazacyclotetradecane-1-acetate, Li(cyclamacetate), with FeCl3 yields, upon addition of KPF6, [(cyclam-acetato)FeCl]PF6 (1) as a red microcrystalline solid. Addition of excess NaN3 prior to addition of KPF6 yields the azide derivative [(cyclam-acetato)FeN3]PF6 (2a) as orange microcrystals. The X-ray crystal structure of the azide derivative has been determined as the tetraphenylborate salt (2b). Reaction of 1 with silver triflate yields [(cyclam-acetato)Fe(O3SCF3)]PF6 (3), which partially dissociates triflate in nondried solvents to yield a mixture of triflate and aqua bound species. Each of the iron(III) derivatives is low-spin (d(5), S = 1/2) as determined by variable-temperature magnetic susceptibility measurements, Mossbauer and EPR spectroscopy. The low-spin iron(II) (d(6), S = 0) complexes 1(red) and 2a(red) have been prepared by electrochemical and chemical methods and have been characterized by Mossbauer spectroscopy. Photolysis of 2a at 419 nm in frozen acetonitrile yields a nearly colorless species in approximately 80% conversion with an isomer shift delta = -0.04 mm/s and a quadrupole splitting DeltaE(Q) = -1 67 mm/s. A spin-Hamiltonian analysis of the magnetic Mossbauer spectra is consistent with an Fe-V ion (d(3), S = 3/2). The proposed [(cyclam-acetato)Fe-V=N](+) results from the photooxidation of 2a via heterolytic N-N cleavage of coordinated azide. Photolysis of 2a in acetonitrile solution at -35 degreesC (300 nm) or 20 degreesC (Hg immersion lamp) results primarily in photoreduction via homolytic Fe-N-azide cleavage yielding Fe-II (d,(6) S = 0) with an isomer shift delta = 0.56 mm/s and quadrupole splitting DeltaE(Q) = 0.54 mm/s. A minor product containing high valent iron is suggested by Mossbauer spectroscopy and is proposed to originate from [{(cyclam-acetato)Fe}(2)(mu -N)](2+) With a mixed-valent {Fe-IV(mu -N)Fe-III}4(+) S = 1/2 core. Exposure of 3 to a stream of oxygen/ozone at low temperatures (-80 degreesC) in acetone/water results in a single oxidized product with an isomer shift delta = 0.01 mm/s and quadrupole splitting DeltaE(Q) = 1.37 mm/s. A spin-Hamiltonian analysis of the magnetic Mossbauer yields parameters similar to those of compound II of horseradish peroxidase which are consistent with an Fe-IV=O monomeric complex (S = 1). [References: 61]