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A family of tetradentate ligands, [N,N′-bis(pyridine-2-yl)]ethane-1,2-diamine (L1), [N,N′-bis(pyridine-2-yl)]propane-1,3-diamine (L2) and [N,N′-bis(pyridine-2-yl)]butane-1,4-diamine (L3) has been prepared. These ligands differ only in the number of CH2groups separating two pyridyl/imine moieties, however, in reactions with MnIIand N−3salts, they produce structurally very diverse solids; [Mn2(L1)3(N3)]n(ClO4)3n(1), [Mn2(L2)2(N3)2](PF6)2(2) and [Mn2(L3)(N3)2]n(ClO4)2n(3). Complexes 1, 2and 3consist of azido-bridged magnetically dilute Mn2pairs, arranged as 1-D, discrete and 2-D arrays, respectively. In these materials, the connection between Mn centers within the dinuclear entities occurs through mono-1,3-N−3, bis-1,3-N−3and bis-1,1-N−3bridges, respectively, for 1, 2and 3. Bulk magnetic measurements reveal that the coupling within such units is antiferromagnetic (J= −1.8 cm−1, 1; J= −4.8 cm−1, 2) and ferromagnetic (J= +1.45 cm−1, 3), depending on whether the N−3binding mode is end-to-end (EE) or end-on (EO). The reported values are given according to the convention H= −2JS1S2for the spin-Hamiltonian.

A series of mixed-tris chelates of OsIII and OsIV of the general formula [OsDQ2]0/1+ [D =ß-ketoenolates (D1-D3) or tropolonate (D4); Q = deprotonated 8-quinolinol] has been prepared and characterized by physico-chemical and spectroscopic methods. In MeCN solution the OsN2O4 unit displays reversible OsIV-OsIII and OsIII-OsII couples in the ca. - 1.2 to + 0.3 V range versus s.c.e. An irreversible oxidative response corresponding to a higher degree of oxidation is also observed at ca. 1.6 V. The chemistry in different oxidation states is discussed in terms of the electrochemical results.

The synthesis and characterization of a series of complexes of the type [OsX(B)L2] + (X = Cl or Br, B = pyridine (py) and pyrazine (pyz), L = 2-(phenylazo)pyridine (L1) or 2-(m-tolylazo)pyridine (L2)) is described. The cations have been isolated as crystalline perchlorate monohydrates after purification by column chromatography. The diamagnetic compounds display several spin-allowed and spin-forbidden m.l.c.t. transitions in the visible region. The metal-centred oxidations and ligand-based reductions of the complexes are studied electrochemically in MeCN. Two consecutive one-electron oxidations corresponding to OsIII/OsII and OsIV/OsIII couples occur at ca. 1.3 and ca. 2.3 V versus s.c.e. respectively. Four successive azo-reductions are observable in the potential range -0.4 to -2.4V.

A group of mixed-tris chelates of type [OsAQ2] [A = isonitrosoacetophenonate (A1) and isonitroso-propiophenonate (A2); Q = deprotonated 8-quinolinol (Q1) and 2-methyl-8-quinolinol (Q2)] have been prepared by two distinct synthetic approaches. [OsAQ2]+, obtained by CeIV oxidation of [OsAQ2], can be regenerated by hydrazine hydrate reduction of the former. The complexes, characterized by physico-chemical, magnetic and spectroscopic methods, exhibit several spin-allowed and spin-forbidden charge transfer transitions in their electronic spectra. In MeCN solution the OsN3O3 unit displays a nearly-reversible OsIV-OsIII change and an OsIII-OsII couple in the ca. -1.0– + 0.3V range versus s.c.e. The stability of the metal oxidation levels is discussed in terms of the chemical and electrochemical results.

A high yield synthetic route to osmium mononitrosyls of type [OsX(NO)Q2] (2) [X = Cl or Br, Q = anions of quinolin-8-ol (HQ1) and its substituted species (HQ2)] from [OsX2Q2] (1) is described. The orange-red complexes are diamagnetic and exhibit?(NO) at ca. 1910 cm-1 in their i.r. spectra, indicating a high degree of nitrosonium ion (NO+) character. A single sharp Q2 methyl signal is in line with the geometry of (2). The complexes display both spin-allowed and spin-forbidden charge transfer transitions in the 800–200 nm range. Chemical reactions toward nucleophiles, namely acetylacetone and propiophenone, clearly establish the electrophilic nature of the bound NO.

A group of mixed-tris chelates of osmium(III) and osmium(IV) of type [OsAQ2]0/1 + [HA = glycine (glyH), picolinic acid (PicH) and quinaldic acid (qndH); HQ = 8-quinolinol] were prepared and characterized by physicochemical, magnetic and spectroscopic methods. The complexes exhibit several spin-allowed and spin-forbidden absorption bands and shoulders in the 200–700 nm region. The new chelates are electroactive and display nearly reversible OsIV-OsIII and OsIII-OsII couples in the ca. -1.1 to +0.3 V range versus s.c.e. The stability of metal oxidation states is discussed in terms of the electrochemical results.

A new tetranuclear double-open dicubane complex [Ni₄(μ₂-N₃)₄(μ₃-N₃)₂(N₃)₂(enbzpy)₂]·2H₂O (enbzpy = [N,N-bis(pyridin-2-yl)benzylidene]ethane-1,2-diamine) has been characterised structurally and magnetostructurally.