Syntheses, crystal structures and spectroscopic properties of two Cu2+-doped single crystals containing 3,14-diethyl-2,6,13,17-tetraazatricyclo[16.4.0.07,12]docosane

A Bioinspired Nonheme FeIII-(O22-)-CuII Complex with an St = 1 Ground State

Cytochrome c oxidase (CcO) is a heme copper oxidase (HCO) that catalyzes the natural reduction of oxygen to water. A profound understanding of some of the elementary steps leading to the intricate 4e-/4H+ reduction of O2 is presently lacking. A total spin St = 1 FeIII-(O22-)-CuII (IP) intermediate is proposed to reduce the overpotentials associated with the reductive O-O bond rupture by allowing electron transfer from a tyrosine moiety without the necessity of any spin-surface crossing. Direct evidence of the involvement of IP in the CcO catalytic cycle is, however, missing. A number of heme copper peroxido complexes have been prepared as synthetic models of IP, but all of them possess the catalytically nonrelevant St = 0 ground state resulting from antiferromagnetic coupling between the S = 1/2 FeIII and CuII centers. In a complete nonheme approach, we now report the spectroscopic characterization and reactivity of the FeIII-(O22-)-CuII intermediates 1 and 2, which differ only by a single -CH3 versus -H substituent on the central amine of the tridentate ligands binding to copper. Complex 1 with an end-on peroxido core and ferromagnetically (St = 1) coupled FeIII and CuII centers performs H-bonding-mediated O-O bond cleavage in the presence of phenol to generate oxoiron(IV) and exchange-coupled copper(II) and PhO• moieties. In contrast, the μ-η2:η1 peroxido complex 2, with a St = 0 ground state, is unreactive toward phenol. Thus, the implications for spin topology contributions to O-O bond cleavage, as proposed for the heme FeIII-(O22-)-CuII intermediate in CcO, can be extended to nonheme chemistry.

Crystal structure of cis-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N)bis-(thio-cyanato-κN)chromium(III) bromide from synchrotron X-ray diffraction data

The crystal structure of the title complex, cis-[Cr(NCS)2(cyclam)]Br (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-decane, C10H24N4), has been determined from synchrotron X-ray data. The asymmetric unit contains one [Cr(NCS)2(cyclam)]+ cation and one bromide anion. The CrIII ion of the complex cation is coordinated by the four N atoms of the cyclam ligand and by two N-coordinating NCS groups in a cis arrangement, displaying a distorted octa-hedral coordination sphere. The Cr-N(cyclam) bond lengths are in the range 2.075 (3) to 2.081 (3) Å while the average Cr-N(NCS) bond length is 1.996 (16) Å. The macrocyclic cyclam moiety adopts the most stable cis-V conformation. The crystal structure is stabilized by inter-molecular hydrogen bonds involving the cyclam N-H groups as donor groups, and the bromide anion and the S atom of one of the NCS ligands as acceptor groups.