Density functional theory investigations of NiN2S2 reactivity as a function of nitrogen donor type and N-H...S hydrogen bonding inspired by nickel-containing superoxide dismutase.

Density functional theory calculations on a series of six square-planar NiN2S2 complexes have been performed. The nitrogen donor type was varied from diamino in Ni(bme-dmed), 1, to amino-amido in [Ni(mama)]-, 2, to diamido in [Ni(ema)]2-, 3. The sulfur-oxygenated derivative Ni(bme-O2-dmed), 4, and hydrogen-bonded derivatives (5 and 6) of 2 and 3 were also studied. Full geometric optimization and subsequent population analyses were performed using the 6-311g(d,p) basis set. The frontier molecular orbitals for all complexes contain significant nickel and sulfur character. Molecular electrostatic potentials show that amido nitrogen donors increase electron density at nickel relative to sulfur. Sulfur modification further shifts electron density away from the ligand towards the metal. It is proposed that the nitrogen donor type and sulfur modification may regulate sulfur-site reactivity in nickel-containing superoxide dismutase.

Molecular and electronic structure of [Mn(V)N(cyclam-acetato)]PF6. A combined experimental and DFT study.

From the reaction of Li(cyclam-acetate), MnCl(2).4H(2)O, and KPF(6) in methanol brown microcrystals of [Mn(III)Cl(cyclam-acetato)]PF(6) (1) were obtained in the presence of air (cyclam-acetic acid = 1,4,8,11-tetraazacyclotetradecane-1-acetic acid). The reaction of 1 in aqueous NH(3) solution with NaOCl produced blue crystals of [Mn(V)N(cyclam-acetato)]PF(6) (2). Complexes 1 and 2 were characterized by single-crystal X-ray crystallography, IR and Raman, electronic absorption, and (1)H, (13)C, and (15)N NMR spectroscopies. Their magnetochemistry as well as their electrochemistry have been investigated. The complexes [MnN(cyclam-acetato)](+/2+) were studied by theoretical calculations at the DFT and semiempirical levels in order to obtain more insight into the ground and excited states of the Mn(V)(triple bond)N unit. Structural and spectroscopic parameters were successfully calculated and compared to experiment. A pictorial description of the bonding has been developed.

Subtle bite-angle influences on N(2)S(2)Ni complexes.

A new N(2)S(2)Ni complex based on the 1,4-diazacycloheptane (dach) framework allows the study of the effects of ring size, in fused diamines, on the structural and chemical properties of nickel(II) dithiolate and dithioether complexes. Compared to its 1,5-diazacyclooctane (daco) derivatives, the dithiolate complex (bmedach)Ni and the S-templated, macrocyclic dithioether complex (propyl-bmedach)NiBr(2) show decreased cavity sizes with narrower angleN-Ni-N angles (by ca. 6 degrees ) and wider angleS-Ni-S angles (also by ca. 6 degrees ). The electrochemical properties of the dithiolate complexes based on dach and daco are nearly identical, while the (propyl-bmedach)NiBr(2) complex shows a 140 mV destabilization of the Ni(I) oxidation state relative to its daco analogue. Molecular structures for the (bmedach)Ni and (propyl-bmedach)NiBr(2) complexes and their respective electrochemical and spectroscopic properties are reported.

Mononuclear (nitrido)iron(V) and (oxo)iron(IV) complexes via photolysis of [(cyclam-acetato)FeIII(N3)]+ and ozonolysis of [(cyclam-acetato)FeIII(O3SCF3)]+ in water/acetone mixtures.

Reaction of the monoanionic, pentacoordinate ligand lithium 1,4,8,11-tetraazacyclotetradecane-1-acetate, Li(cyclam-acetate), 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 (d5, S = 1/2) as determined by variable-temperature magnetic susceptibility measurements, Mössbauer and EPR spectroscopy. The low-spin iron(II) (d6, S = 0) complexes 1red and 2ared have been prepared by electrochemical and chemical methods and have been characterized by Mössbauer 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 delta EQ = -1.67 mm/s. A spin-Hamiltonian analysis of the magnetic Mössbauer spectra is consistent with an FeV ion (d3, S = 3/2). The proposed [(cyclam-acetato)FeV=N]+ results from the photooxidation of 2a via heterolytic N-N cleavage of coordinated azide. Photolysis of 2a in acetonitrile solution at -35 degrees C (300 nm) or 20 degrees C (Hg immersion lamp) results primarily in photoreduction via homolytic Fe-Nazide cleavage yielding FeII (d,6 S = 0) with an isomer shift delta = 0.56 mm/s and quadrupole splitting delta EQ = 0.54 mm/s. A minor product containing high-valent iron is suggested by Mössbauer spectroscopy and is proposed to originate from [((cyclam-acetato)Fe)2(mu-N)]2+ with a mixed-valent (FeIV(mu-N)FeIII))4+S = 1/2 core. Exposure of 3 to a stream of oxygen/ozone at low temperatures (-80 degrees C) in acetone/water results in a single oxidized product with an isomer shift delta = 0.01 mm/s and quadrupole splitting delta EQ = 1.37 mm/s. A spin-Hamiltonian analysis of the magnetic Mössbauer yields parameters similar to those of compound II of horseradish peroxidase which are consistent with an FeIV=O monomeric complex (S = 1).