Flavodiiron nitric oxide reductases (FNORs), found in many pathogenic bacteria, are able to detoxify NO by reducing it to N2O. In this way, FNORs equip these pathogens with immunity to NO, which is a central immune defense agent in humans. Hence, FNORs are thought to promote infection of the human body, leading to chronic diseases. Despite this importance of FNORs for bacterial pathogenesis, the mechanism of NO reduction by these enzymes is not well understood. Here we present the synthesis and spectroscopic characterization of the diiron dinitrosyl model complex [Fe2(BPMP)(OPr)(NO)2](BPh4)2. The crystal structure of this complex shows two end-on-coordinated {FeNO}(7) units that, based on spectroscopic and electrochemical results, are only weakly electronically coupled. Importantly, reduction of this complex by two electrons leads to the clean formation of N2O in quantitative yield. This complex therefore represents the first example of a functional model system for FNORs. The results provide key mechanistic insight into the mechanism of FNORs and, in particular, represent strong support for the proposed "super-reduced" mechanism for these enzymes.

Three paramagnetic heterobimetallic lantern complexes of the form [PtM(tba) 4 (OH 2 )] (M ¼ Fe, 1; Co, 2; Ni, 3; tba ¼ thiobenzoate) have been prepared in a single-step, bench-top procedure. In all three cases, a lantern structure with Pt-M bonding is observed in solution and in the solid state. Compound 1 is a monomer whereas 3 exists as a dimer in the solid state via a Pt/Pt metallophilic interaction. Compound 2 has been characterized in forms with (2a, purple) and without (2b, yellow) Pt/Pt metallophilic interactions. The dimers 2a (J ¼ À10 cm À1 , based on the spin Hamiltonian Ĥ ¼ À2J (S A $S B )) and 3 (J ¼ À60 cm À1 ) exhibit antiferromagnetic coupling between the two first-row metal ions in the solid state via a Pt/Pt non-covalent metallophilic interaction. The electronic structure ofNi, units have been studied with DFT calculations, confirming the relative spin-state energies observed and the antiferromagnetic exchange pathway through four d z 2 orbitals. The compounds 2a and 3 are the first examples of antiferromagnetic coupling through an unbridged M/M contact.

A series of copper complexes bearing new 6-substituted tris(2-pyridylmethyl)amine ligands (L) appended with NH(p-R-CH) groups (R = H, CF, OMe) were prepared. These ligands are electronically tunable (ΔE = 160 mV) and Cu(L) complexes react with oxygen to form hydrogen bonded (trans-1,2-peroxo)dicopper species.