Neutral Cyanide Research Articles

Controlled Synthesis of Heterotrimetallic Single‐Chain Magnets from Anisotropic High‐Spin 3 d–4 f Nodes and Paramagnetic Spacers

By using the node-and-spacer approach in suitable solvents, four new heterotrimetallic 1D chain-like compounds (that is, containing 3d-3d'-4f metal ions), {[Ni(L)Ln(NO(3))(2)(H(2)O)Fe(Tp*)(CN)(3)]⋅2 CH(3)CN⋅CH(3)OH}(n) (H(2)L = N,N'-bis(3-methoxysalicylidene)-1,3-diaminopropane, Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate; Ln = Gd (1), Dy (2), Tb (3), Nd (4)), have been synthesized and structurally characterized. All of these compounds are made up of a neutral cyanide- and phenolate-bridged heterotrimetallic chain, with a {-Fe-C≡N-Ni(-O-Ln)-N≡C-}(n) repeat unit. Within these chains, each [(Tp*)Fe(CN)(3)](-) entity binds to the Ni(II) ion of the [Ni(L)Ln(NO(3))(2)(H(2)O)](+) motif through two of its three cyanide groups in a cis mode, whereas each [Ni(L)Ln(NO(3))(2)(H(2)O)](+) unit is linked to two [(Tp*)Fe(CN)(3)](-) ions through the Ni(II) ion in a trans mode. In the [Ni(L)Ln(NO(3))(2)(H(2)O)](+) unit, the Ni(II) and Ln(III) ions are bridged to one other through two phenolic oxygen atoms of the ligand (L). Compounds 1-4 are rare examples of 1D cyanide- and phenolate-bridged 3d-3d'-4f helical chain compounds. As expected, strong ferromagnetic interactions are observed between neighboring Fe(III) and Ni(II) ions through a cyanide bridge and between neighboring Ni(II) and Ln(III) (except for Nd(III) ) ions through two phenolate bridges. Further magnetic studies show that all of these compounds exhibit single-chain magnetic behavior. Compound 2 exhibits the highest effective energy barrier (58.2 K) for the reversal of magnetization in 3d/4d/5d-4f heterotrimetallic single-chain magnets.

A novel free-standing nanowire substrate with surface enhanced Raman scattering (SERS) activity

Free-standing nickel nanowires supported by a nickel base were electrochemically fabricated on nanoporous alumina templates. A novel technique based on zincating was used for the activation of the pore bottoms of aluminum anodic oxide (AAO) that enabled the direct electrodeposition in the pores. For SERS applications, gold was electrodeposited on free-standing nickel nanowires in a conventional neutral cyanide bath. Under optimized conditions the SERS signal intensity of Rhodamine 6G molecules adsorbed on the nanowires was amplified to the order of 5 × 10 6. The results demonstrate the potential of this easy technique for reproducible SERS substrate preparation and activity.

Structure and stability of neutral cyanide complexes of copper and zinc

A theoretical study of neutral Zn[CN] n and Cu[CN] n complexes has been carried out, as representative examples of cyanide complexes of late transition metals. Both complexes prefer the cyanide arrangement over the isocyanide form, in agreement with the experimental evidence for the monocyanide compounds. The successive complexation energies suggest that the preferred complex in the case of copper is the monocyanide, CuCN, whereas for zinc the most favourable complex seems to be Zn(CN) 2. Both Zn and Cu have preference for low coordination numbers, since mixed complexes with cyanide and cyanogen ligands are preferred over homoleptic M(CN) n complexes for n > 2.

Neutral cyanide complexes of iron: Structure and stability

Neutral iron-cyanide complexes have been studied through computational techniques. Fe[CN] n complexes are shown to prefer the cyanide arrangement. Only in the case of Fe[CN] the isocyanide isomer is found to lie slightly below the cyanide isomer. According to the complexation energies, Fe(CN) 2 seems to be the main target for possible experimental observation in the gas phase. Mixed complexes with cyanide and cyanogen ligands, Fe(CN) x (C 2N 2) y , have also been studied. The balance between the stronger ligand character of CN and the preference for low coordination numbers, makes Fe(CN) 2, Fe(CN)(C 2N 2), Fe(CN) 2(C 2N 2), Fe(CN)(C 2N 2) 2, and Fe(CN) 2(C 2N 2) 2 the most stable complexes for each stoichiometry.

Dimolybdenum–μ-cyanide complexes supported by N-tert-butylanilide ligation: in pursuit of cyanide reductive cleavage

The red cyanide complex (NC)Mo(N[R]Ar)_3 (R=C(CD_3)_2CH_3, Ar=3,5-C_6H_3Me_2) was prepared in 77% yield by reaction of iodide IMo(N[R]Ar)_3 with tetra-n-butyl ammonium cyanide. By reaction of cyanide (NC)Mo(N[R]Ar)_3 with the three-coordinate molybdenum(III) complex Mo(N[R]Ar)_3 was prepared the dimolybdenum-μ-cyanide complex (μ-CN){Mo(N[R]Ar)_3}_2 as a violet solid in 80% yield. Reduction of μ-cyanide (μ-CN){Mo(N[R]Ar)_3}_2 by one electron would give a cyanide-bridged anion isoelectronic with the known μ-N_2 complex (μ-N_2){Mo(N[R]Ar)_3}_2, an intermediate in dinitrogen cleavage to two equivalents of nitride NMo(N[R]Ar)_3 by Mo(N[R]Ar)_3. Instead of undergoing an analogous cleavage of cyanide upon one-electron reduction, μ-cyanide (μ-CN){Mo(N[R]Ar)_3}_2 was found to undergo expulsion of a ligand C(CD_3)_2CH_3 substituent upon exposure to reducing conditions, the product isolated in 50% yield being imido–μ-cyanide (Ar[R]N)_2(ArN)Mo(μ-NC)Mo(N[R]Ar)_3. By reaction of [N^nBu_4][CN] with the 1-adamantyl-substituted molybdenum complex Mo(N[Ad]Ar)_3, the blue salt [N^nBu_4][(NC)Mo(N[Ad]Ar)_3] was obtained in 91% yield. Reaction of ferrocenium triflate or silver triflate with [N^nBu_4][(NC)Mo(N[Ad]Ar)_3] gave ferrocene or silver along with the neutral cyanide complex (NC)Mo(N[Ad]Ar)_3, isolated in 74% yield. While reaction of (NC)Mo(N[Ad]Ar)_3 with Mo(N[R]Ar)_3 gave in 53% yield a burgundy-colored dimolybdenum–μ-cyanide complex (Ar[Ad]N)_3Mo(μ-CN)Mo(N[R]Ar)_3. the 1-adamantyl-substituted cyanide did not exhibit any reaction with the 1-adamantyl-substituted tricoordinate complex Mo(N[Ad]Ar)_3. The latter results indicate that cyanide is too small to serve as a bridge for two equivalents of the highly sterically encumbered Mo(N[Ad]Ar)_3 fragment. A metathetical route to a heterodinuclear cyanide-bridged complex was explored involving addition of [N^nBu_4][(NC)Mo(N[Ad]Ar)_3] to the vanadium iodide complex IV(N[R]Ar_F)_2. By this reaction was obtained the orange–brown μ-cyanide complex (Ar_F[R]N)_2V(μ-NC)Mo(N[Ad]Ar)_3 in 30% recrystallized yield. The latter was characterized by X-ray crystallography. The cyanide chemistry reported here is interpreted with the aid of bonding considerations and cyclic voltammetry studies on the new complexes.

Fabrication of tenth of micron stress minimized electroplated gold patterns for x-ray lithography masks

An optimized gold direct current (dc) electroplating process from a cyanide bath was developed for the fabrication of x-ray lithography masks. The stress behavior of 0.4–2 μm thick gold thin films dc electrodeposited from a neutral cyanide bath was studied as a function of their deposition parameters. Temperatures in the 40–70 °C range and current densities varying from 1 to 10 mA/cm2 were used. Deposits with low total tensile stress (down to 10 MPa) were obtained. The influence of the plating base was addressed. A structuring process was developed, which enabled the fabrication of 0.65 μm thick gold patterns for x-ray lithography masks. The minimum linewidth obtained was 70 nm in a single layer process and 0.2 or 0.3 μm period gratings in a single layer or trilayer stencil, respectively. The problem of thickness uniformity in the deposits was also studied.

Synthesis of octahedral carbonyl complexes of manganese(I) with SCN or CN ligands. Crystal structure of fac-[SCNMn(CO) 3(dppm)

The complexes fac-[XMn(CO) 3(dppm)], cis, cis-[XMn(CO) 2(dppm)(P(OPh) 3)] and trans-[XMn(CO)(dppm) 2] with X = SCN or CN have been prepared from the corresponding bromocarbonyls and the salts AgX or KX, or, in the case of the di- and mono-carbonyls, from fac-[XMn(CO) 3(dppm)] with X = SCN or CN by thermal or photochemical CO substitution by the ligands P(OPh) 3 or dppm. The structure of fac-[SCNMn(CO) 3(dppm)] has been determined by X-ray diffraction. The crystals are monoclinic, space group P2 1/ n, and the structure has been refined to R = 0.058 for 4123 reflexions measured in the range 2 ⩽ θ ⩽ 30 at room temperature. The cis, cis-[NCMn(CO) 2(dppm)(P(OPh) 3)] complex can be oxidized and subsequently reduced to the isomer trans-[NCMn(CO) 2(dppm)(P(OPh) 3)]. All the neutral cyanide complexes react readily with MeI and KPF 6 to give the corresponding methylisocyanide derivatives [Mn(CO) 2(dppm)(P(OPh) 3)(CNMe)]PF 6 and [Mn(CO)(dppm) 2(CNMe)]PF 6. The stereochemistries of the compounds is discussed in relation to the 31P NMR spectra.

A New Concept for Electroplated Electronic Contact Golds

Due to the shortcomings of the present-day standard gold/cobalt and gold/nickel low-alloy contact golds, especially from aspects of high-temperature storage (approximately 125°C for 1000 h plus) and also their consistent risk of spontaneous cracking and solution operating difficulties, efforts were made to deviate from this thinking. The deposit was required to have low porosity at approximately 2-2.5-µm deposit thicknesses. Solution parameters were required to be broad without adverse influence on deposit characteristics. The resistance of the solution to metallic and organic contamination was also considered. A bath of high-cathode efficiency with good throwing power and with a wide permissible current density spectrum was also regarded as essential to the industry. A deposit of gold of approximately one percent cadmium and one percent organic polymer was finally selected, being plated from solutions based on neutral cyanide systems. It is considered that this alloy heralds a new generation of gold deposits for electrical contacts.

Compatibility of Gold Deposits for Connector Contacts

A forty way, two part, printed circuit board connector has been the test vehicle for the evaluation of wear of a number of gold deposits in similar and dissimilar combinations. The proprietary electrolytes, from four suppliers, consisted of four acid cyanide types (cobalt or nickel hardened) two noncyanide (sulphite) and two neutral cyanide organically hardened golds. Assessment of wear was made by scanning electron microscope examination of wear tracks and by changes in contact resistance when the connectors were subsequently exposed to a corrosive environment. The acid Cyanide deposits exhibited least wear, the sulphite types wore excessively by cold pressure welding to produce platelets of debris, and the neutral cyanide golds were of mixed extent of wear. A hypothesis involving a polymer lubrication mechanism is proposed to explain the Iow wear of the acid golds. Scanning electron micrographs support this pro- posal.

Electrochemical characteristics of manganese in cyanide solutions: I. Polarography of manganese(I), (II), and (III)

In neutral sodium cyanide solutions, manganese(II) is reversibly reduced to the + I state at a dropping mercury electrode. The half-wave potential of the resulting polarographic wave is −1.364 ± 0.007 V vs S.C.E. in 1 F sodium cyanide, and varies with sodium cyanide concentration in a manner that can be ascribed to activity effects. The value of i d / C for this wave decreases on adding sodium hydroxide, on increasing the manganese(II) concentration, and (at an anomalous rate) on increasing the drop time. These facts indicate that manganese(I) reacts with hydrogen cyanide to regenerate manganese(II), and that this reaction is fractional order with respect to manganese(I). Direct polarographic and spectrophotometric measurements of the rates of decomposition of air-free cyanide solutions of manganese (I) give for the pseudo-half-order rate constant ▪ The absorption spectra of very dilute (0.02–0.05 m F) solutions of manganese(I) in cyanide media indicate the presence of more than one absorbing species. Adding sodium hydroxide to a solution of manganese(II) in 1 F sodium cyanide results in a reaction which is probably best represented by the equation ▪ and the resulting hydroxocyano complex undergoes an irreversible 2-electron reduction to the metal at E 1 2 = −1.72 V. The data do not appear to confirm the supposition that Mn(CN) 6 4− is the sole important species of manganese (II) in moderately concentrated neutral cyanide solutions. Manganese(III) is the principal product of the oxidation of manganese(II) with air or oxygen in neutral cyanide media, but the reaction is not stoichiometric. At high concentrations of manganese and/or cyanide, the oxidation is incomplete even though, very prolonged; at low concentrations of both, substantial amounts of a more highly oxidized species are present. Manganese(III) in neutral cyanide media is polarographically reduced to the +1 state in two successive 1-electron steps.

On the binding of copper by hemocyanin

One new sulfhydryl group can be determined by amperometric silver titration in several denaturing media, for each four atoms of copper removed from hemocyanin by anaerobic dialysis with neutral cyanide.