Reaction of cis-[FeIII(cyclam)Cl2]Cl in acidic H2O/CH3OH or CH3CN/H2O mixtures with NaN3 at 50 °C produced upon addition of NaClO4 or NaPF6 the complex trans-[FeIII(cyclam)(N3)2]ClO4 (1a) or the hexafluorophosphate salt 1b, whereas at −18 °C the same reaction produced cis-[FeIII(cyclam)(N3)2](ClO4) (2) (cyclam = 1,4,8,11-tetraazacyclotetradecane). The crystal structures of 1b and 2 were determined by single-crystal X-ray crystallography. Complexes 1a, b, contain a low-spin (S = 1/2) and 2, a high-spin ferric ion (S = 5/2) as was established by variable-temperature magnetic susceptibility measurements and Mossbauer and X-band EPR spectroscopy. The low-spin trans-[(cyclam)FeII(N3)2] and high-spin cis-[(cyclam)FeII(N3)2] species were generated electrochemically in CH3CN solution and were characterized by Mossbauer spectroscopy. Photolysis of 1a in CH3CN at −35 °C and 20 °C with a Hg immersion lamp generated within 15 min a yellow solution. EPR and Mossbauer spectra show that a single high-valent species with...

Photolysis of cis- and trans-[FeIII(cyclam)(N3)2]+ Complexes: Spectroscopic Characterization of a Nitridoiron(V) Species

Monovalent, trivalent and tetravalent nickel

From the reaction of cis-[(cyclam)FeIII(Cl)2]Cl (cyclam = 1,4,8,11-tetraazacyclotetradecane) with hydroxylamine in water the octahedral nitrosyliron complexes trans-[(cyclam)Fe(NO)Cl](ClO4) (1) and cis-[(cyclam)Fe(NO)I]I (2) have been isolated as crystalline solids. EPR spectroscopy and variable-temperature susceptibility measurements established that 1 possesses an S = 1/2 and 2 an S = 3/2 ground state; both species are of the {Fe−NO}7 type. Electrochemically, 1 can be reversibly one-electron oxidized yielding trans-[(cyclam)Fe(NO)Cl]2+, an {Fe−NO}6 species, and one-electron reduced yielding trans-[(cyclam)Fe(NO)Cl]0, an {Fe−NO}8 species. These complexes have been characterized in CH3CN solutions by UV−vis and EPR spectroscopy; both possess a singlet ground state. All of these nitrosyliron complexes, including [LFe(NO)(N3)2] (S = 3/2; L = 1,4,7-trimethyl-1,4,7-triazacyclononane) and [L‘Fe(NO)(ONO)(NO2)](ClO4) (S = 0; L‘ = 1,4,7-triazacyclononane), have been studied by variable-temperature Mossbauer spect...

The Electronic Structures of an Isostructural Series of Octahedral Nitrosyliron Complexes {Fe−NO}6,7,8 Elucidated by Mössbauer Spectroscopy

Two new azido-bridged polyoxometalate compounds were synthesized in acetonitrile/methanol media and their molecular structures have been determined by X-ray crystallography. The [[(gamma-SiW10O36)Mn2(OH)2(N3)(0.5)(H2O)(0.5)]2(mu-1,3-N3)](10-) (1 a) tetranuclear Mn(III) complex, in which an end-to-end N3- ligand acts as a linker between two [(gamma-SiW10O36)Mn2(OH)2]4- units, represents the first manganese-azido polyoxometalate. The magnetic properties have been studied considering the spin Hamiltonian H = -J1(S1S2+S1*S2*)-J2(S1S1*), showing that antiferromagnetic interactions between the paramagnetic centers (g = 1.98) occur both through the di-(mu-OH) bridge (J1 = -25.5 cm(-1)) and the mu-1,3-azido bridge (J2 = -19.6 cm(-1)). The [(gamma-SiW10O36)2Cu4(mu-1,1,1-N3)2(mu-1,1-N3)2]12- (2 a) tetranuclear Cu(II) complex consists of two [gamma-SiW10O36Cu2(N3)2]6- subunits connected through the two mu-1,1,1-azido ligands, the four paramagnetic centers forming a lozenge. The magnetic susceptibility data have been fitted. This reveals ferromagnetic interactions between the four Cu(II) centers, leading to an S=2 ground state (H = -J1(S1S2+S1*S2*)-J2(S2S2*), J1 = +294.5 cm(-1), J2 = +1.6 cm(-1), g = 2.085). The ferromagnetic coupling between the Cu(II) centers in each subunit is the strongest ever observed either in a polyoxometalate compound or in a diazido-bridged Cu(II) complex. Considering complex 2 a and the previously reported basal-basal di-(mu-1,1-N3)-bridged Cu(II) complexes in which the metallic centers are not connected by other magnetically coupling ligands, the linear correlation J1 = 2639.5-24.95*theta(av) between the theta(av) bridging angle and the J1 coupling parameter has been proposed. The electronic structure of complex 2 a has also been investigated by using multifrequency high-field electron paramagnetic resonance (HF-EPR) spectroscopy between 95 and 285 GHz. The spin Hamiltonian parameters of the S = 2 ground state (D = -0.135(2) cm(-1), E = -0.003(2) cm(-1), g(x) = 2.290(5), g(y) = 2.135(10), g(z) = 2.158(5)) as well as of the first excited spin state S = 1 (D = -0.960(4) cm(-1), E = -0.080(5) cm(-1), g(x) = 2.042(5), g(y) = 2.335(5), g(z) = 2.095(5)) have been determined, since the energy gap between these two spin states is very small (1.6 cm(-1)).

Structural and Magnetic Properties of MnIII and CuII Tetranuclear Azido Polyoxometalate Complexes: Multifrequency High‐Field EPR Spectroscopy of Cu4 Clusters with S=1 and S=2 Ground States

The positive axial zero-field splitting parameter D relevant for the S = 2 ground state of [Mn(cyclam)I2]I (cyclam = 1,4,8,11-tetraazacyclotetradecane) is interpreted using the valence bond configuration interaction model which explicitly considers the covalency of the manganese-iodide bond.

Is the axial zero-field splitting parameter of tetragonally elongated high-spin manganese(III) complexes always negative?

The syntheses and characterization of complexes of the type cis-[FeX2(L4)]+[L4= 1,4,8,11-tetra-azacyclotetradecane (cyclam); X = Cl, Br, and NCS] and trans-[MX2(L4)]+(M = Mn, X = Cl, Br, NCS, or N3; M = Fe, X = Cl, Br, or NCS: and M = Ni, X = Cl or Br) are described. The assignment of geometrical configuration to these complexes is made on the basis of their i.r. spectra in the 790–910 cm–1 region. In some cases, the assignment of a trans configuration to the dihalogeno-complexes is confirmed by the presence of only one ν(M–X) stretching frequency in their far-i.r. spectra. Magnetic susceptibilities show that all the d4 complexes prepared are high spin, whereas d6 and d7 complexes are low spin. For the d5 iron(III) system, all the cis complexes prepared are high spin, whereas trans complexes are low spin. However, trans-[FeBr2(L4)][ClO4] with µ295 3.90 B.M. appears to be in a high-spin–low-spin equilibrium at room temperature. The ambidentate thiocyanate ligand is N-bonded in each case. The electronic and far-i.r. spectra of these complexes are consistent with the electronic structures based on the magnetic properties.

Structural and mechanistic studies of co-ordination compounds. Part XII. Syntheses and characterization of some dianiono(1,4,8,11-tetra-azacyclotetradecane)-manganese(III), -iron(III), and -nickel(III) salts

Structural and mechanistic studies of coordination compounds. part xiii. syntheses and characterization of some dianiono(1,4,8,11-tetraazacyclotetradecane)manganese(iii), -iron(iii), and -nickel(iii) salts

Pui-Ki Chan

Papers

Structural and mechanistic studies of co-ordination compounds. Part XII. Syntheses and characterization of some dianiono(1,4,8,11-tetra-azacyclotetradecane)-manganese(III), -iron(III), and -nickel(III) salts

Structural and mechanistic studies of coordination compounds. part xiii. syntheses and characterization of some dianiono(1,4,8,11-tetraazacyclotetradecane)manganese(iii), -iron(iii), and -nickel(iii) salts