Two new hybrid organic/inorganic copper(II)-oxovanadate(V) diphosphonates: [Cu2(phen)2(O3PCH2PO3)(V2O5)(H2O)] x H2O and [Cu2(phen)2(O3P(CH2)3PO3)(V2O5)] x C3H8. Synthesis, structure, and magnetic properties

Two new hybrid organic/inorganic copper oxovanadium diphosphonates [Cu2(phen)2(O3PCH2PO3)(V2O5)(H2O)] x H2O (1) and [(Cu2(phen)2(O3P(CH2)3PO3)(V2O5)] x C3H8 (2) have been obtained by hydrothermal synthesis. The compounds are monoclinic, and they crystallize in the space group P2(1)/n with cell parameters of a = 11.788(2) A, b = 17.887(3) A, c = 14.158(2) A, and beta = 93.99(0) degrees and in the space group C2/c with cell parameters of a = 11.025(1) A, b = 18.664(2) A, c = 15.054(2) A, and beta = 90.06(0) degrees, respectively. Both compounds present two-dimensional frameworks built up from infinite chains of corner-sharing vanadium tetrahedra and diphosphonate groups connected by copper tetramers for (1) and copper dimers for (2). The remarkable feature of (2) is the encapsulation of propane molecules, stabilized by strong hydrogen bonding between the layers. The magnetic properties of the compounds have been investigated showing antiferromagnetic coupling with Tmax = 64 K for (1) and Curie-like paramagnetic behavior for (2).     

Synthesis and pyrolysis of silicon and tin containing poly(2,2′-dioxy-1,1′-biphenoxy-phosphazenes)

The polyphosphazene {[NP(O₂C₁₂H₈)]_0.5[NP(OC₆H₄Br)₂]_0.5}_n (1) [(O₂C₁₂H₈) = 2,2′-dioxy-1,1′-biphenyl] that, as an strictly alternating copolymer, can be considered nearly as the homopolymer [NP(O₂C₁₂H₈)NP(OC₆H₄Br)₂]_n, was reacted first with ^tBuLi in THF at −78 °C to give the intermediate [NP(O₂C₁₂H₈)NP(OC₆H₄Li)₂]_n (2) and subsequently with the chlorosilanes SiMe₃Cl and SiMe₂(C₆H₅)Cl or with the chlorostannane SnMe₃Cl, to obtain the new polyphosphazenes {(NP[O₂C₁₂H₈])_0.5[NP(OC₆H₄SiMe₃)₂]_0.5−x[NP(OC₆H₅)(OC₆H₄SiMe₃)]_x}_n (3a) (x = 0.15-0.5), {(NP[O₂C₁₂H₈])_0.5[N(POC₆H₄SiMe₂Ph)₂]_0.2[NP(OC₆H₅)(OC₆H₄SiMe₂Ph)]_0.3}_n (3b), and {(NP[O₂C₁₂H₈])_0.5[NP(OC₆H₅)(OC₆H₄SnMe₃)]_0.5}_n (4), having a very regular distribution of the silicon or tin organometallic sites along the chains. The pyrolysis of the polymers in air at 800 °C gave microcrystalline residues (characterized by IR, XRD, SEM and TEM-EDXA) consisting on phases of SiO₂ · P₂O₅ · P₂O_7.9 · SiP₂O₇, or, in the case of the tin derivative, almost pure SnP₂O₇. The results indicate that, while part of the Si content is lost during the pyrolysis, almost all the tin in the original polymer was incorporated to the final residue.     

Corrosion properties of nickel coatings obtained from aqueous and nonaqueous electrolytes

Nickel was deposited on a copper substrate from aqueous and nonaqueous ethanol electrolytes. X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and chronovoltametry, scanning electron microscopy, and atomic force microscopy were used to study the effect of the solvent on the surface and corrosion properties of the Ni coatings formed. Unifom and relatively smooth Ni films were obtained as measured with microscopy techniques. The formation of a passive film in acidic, alkaline, and neutral chloride-containing media was confirmed with X-ray photoelectron spectroscopy. The water-based nickel-plating electrolyte makes it possible to deposit coatings with higher corrosion resistance as compared with coatings deposited from ethanol electrolyte in NaOH and NaCl media. The proposed mechanism of corrosion in a 0.5 M H₂SO₄ solution involves cycles of active-passive surface behavior due to its passivation by corrosion products.     

Comparative study of two chemically isostructural polymers: [Cu2(VO2)(HPO4)2(NO3)(bpy)2]·2H2O/H3PO4 (bpy is 2,2′‐bi­pyridine)

The title compounds, poly­[bis(2,2′‐bi­pyridine)­bis(μ₃‐hydrogen phosphato)­nitratodi‐μ₂‐oxo‐dicopper(II)­vanadium dihydrate], [Cu₂(VO₂)(HPO₄)₂(NO₃)(C₁₀H₈N₂)₂]·2H₂O, (I), and poly­[bis(2,2′‐bi­pyridine)­bis(μ₃‐hydrogen phosphato)­nitratodi‐μ₂‐oxo‐dicopper(II)­vanadium phospho­ric acid solvate], [Cu₂(VO₂)(HPO₄)₂(NO₃)(C₁₀H₈N₂)₂]·H₃PO₄, (II), were obtained by similar hydro­thermal methods but under different crystallization conditions. The trinuclear entity which serves as the basic unit in both structures presents two independent Cu^II ions immersed in similar square‐pyramidal N₂O₃ environments plus an octahedral VO₆ core and is organized into a one‐dimensional polymer, which is essentially identical in the two structures. The compounds are stabilized by different solvates, viz. two crystallization water mol­ecules in (I) and a phospho­ric acid mol­ecule in (II), which provide the main structural differences through the diversity of interchain interactions in which they serve as bridges.     

Synthesis and Characterization of N3P3(O2C12H8)2(OC6H4Si(CH3)3)(OC6H4Br) and Its Conversion to Nanostructured Si Material

A new silicated cyclotriphosphazene N₃P₃(O₂C₁₂H₈)₂(OC₆H₄Si(CH₃)₃)(OC₆H₄Br) 1 has been synthesized and characterized. The solid state pyrolysis of 1 in air gives a nanostructured SiP₂O₇ 3D network. The morphology of the network strongly depends on the temperature of the pyrolysis. Spinal-like columns and ring-shaped SiP₂O₇ are formed at 800 °C, while, at 600 °C, fused grains of about 300 nm were observed. Based on air TG and DSC thermal studies, we propose the mechanism of formation for the nanostructured network.