Kinetics and mechanism of platinum-thallium bond formation: the binuclear [(CN)5Pt-Tl(CN)](-) and the trinuclear [(CN)5Pt-Tl-Pt(CN)5](3-) complex

Formation kinetics of the metal-metal bonded binuclear [(CN)(5)Pt-Tl(CN)](-) (1) and the trinuclear [(CN)(5)Pt-Tl-Pt(CN)(5)](3-) (2) complexes is studied, using the standard mix-and-measure spectrophotometric method. The overall reactions are Pt(CN)(4)(2-) + Tl(CN)(2)(+) <==> 1 and Pt(CN)(4)(2-) + [(CN)(5)Pt-Tl(CN)](-) <==> 2. The corresponding expressions for the pseudo-first-order rate constants are k(obs) = (k(1)[Tl(CN)(2)(+)] + k(-1))[Tl(CN)(2)(+)] (at Tl(CN)(2)(+) excess) and k(obs) = (k(2b)[Pt(CN)(4)(2-)] + k(-2b))[HCN] (at Pt(CN)(4)(2-) excess), and the computed parameters are k(1) = 1.04 +/- 0.02 M(-2) s(-1), k(-1) = k(1)/K(1) = 7 x 10(-5) M(-1) s(-1) and k(2b) = 0.45 +/- 0.04 M(-2) s(-1), K(2b) = 26 +/- 6 M(-1), k(-2b) = k(2b)/K(2b) = 0.017 M(-1) s(-1), respectively. Detailed kinetic models are proposed to rationalize the rate laws. Two important steps need to occur during the complex formation in both cases: (i) metal-metal bond formation and (ii) the coordination of the fifth cyanide to the platinum site in a nucleophilic addition. The main difference in the formation kinetics of the complexes is the nature of the cyanide donor in step ii. In the formation of [(CN)(5)Pt-Tl(CN)](-), Tl(CN)(2)(+) is the source of the cyanide ligand, while HCN is the cyanide donating agent in the formation of the trinuclear species. The combination of the results with previous data predict the following reactivity order for the nucleophilic agents: CN(-) > Tl(CN)(2)(+) > HCN.     

Kinetics and mechanism of the interaction of nitric oxide with pentacyanoferrate(II). Formation and dissociation of [Fe(CN)5NO]3 -

The interaction of NO with [Fe(CN)(5)H(2)O](3)(-) (generated by aquation of the corresponding ammine complex) to produce [Fe(CN)(5)NO](3)(-) was studied by UV-vis spectrophotometry. The reaction product is the well characterized nitrosyl complex, described as a low-spin Fe(II) bound to the NO radical. The experiments were performed in the pH range 4-10, at different concentrations of NO, temperatures and pressures. The rate law was first-order in each of the reactants, with the specific complex-formation rate constant, k(f)( )()= 250 +/- 10 M(-)(1) s(-)(1) (25.4 degrees C, I = 0.1 M, pH 7.0), DeltaH(f)() = 70 +/- 1 kJ mol(-)(1), DeltaS(f)() = +34 +/- 4 J K(-)(1) mol(-)(1), and DeltaV(f)() = +17.4 +/- 0.3 cm(3) mol(-)(1). These values support a dissociative mechanism, with rate-controlling dissociation of coordinated water, and subsequent fast coordination of NO. The complex-formation process depends on pH, indicating that the initial product [Fe(CN)(5)NO](3)(-) is unstable, with a faster decomposition rate at lower pH. The decomposition process is associated with release of cyanide, further reaction of NO with [Fe(CN)(4)NO](2)(-), and formation of nitroprusside and other unknown products. The decomposition can be prevented by addition of free cyanide to the solutions, enabling a study of the dissociation process of NO from [Fe(CN)(5)NO](3)(-). Cyanide also acts as a scavenger for the [Fe(CN)(5)](3)(-) intermediate, giving [Fe(CN)(6)](4)(-) as a final product. From the first-order behavior, the dissociation rate constant was obtained as k(d) = (1.58 +/- 0.06) x 10(-)(5) s(-)(1) at 25.0 degrees C, I = 0.1 M, and pH 10.2. Activation parameters were found to be DeltaH(d)() = 106.4 +/- 0.8 kJ mol(-)(1), DeltaS(d)() = +20 +/- 2 J K(-)(1) mol(-)(1), and DeltaV(d)() = +7.1 +/- 0.2 cm(3) mol(-)(1), which are all in line with a dissociative mechanism. The low value of k(d) as compared to values for the release of other ligands L from [Fe(II)(CN)(5)L](n)()(-) suggests a moderate to strong sigma-pi interaction of NO with the iron(II) center. It is concluded that the release of NO from nitroprusside in biological media does not originate from [Fe(CN)(5)NO](3)(-) produced on reduction of nitroprusside but probably proceeds through the release of cyanide and further reactions of the [Fe(CN)(4)NO](2)(-) ion.     

Mechanistic diversity covering 15 orders of magnitude in rates: cyanide exchange on [M(CN)(4)](2-) (M = Ni, Pd, and Pt)

Kinetic studies of cyanide exchange on [M(CN)(4)](2-) square-planar complexes (M = Pt, Pd, and Ni) were performed as a function of pH by (13)C NMR. The [Pt(CN)(4)](2-) complex has a purely second-order rate law, with CN(-) as acting as the nucleophile, with the following kinetic parameters: (k(2)(Pt,CN))(298) = 11 +/- 1 s(-1) mol(-1) kg, DeltaH(2) (Pt,CN) = 25.1 +/- 1 kJ mol(-1), DeltaS(2) (Pt,CN) = -142 +/- 4 J mol(-1) K(-1), and DeltaV(2) (Pt,CN) = -27 +/- 2 cm(3) mol(-1). The Pd(II) metal center has the same behavior down to pH 6. The kinetic parameters are as follows: (k(2)(Pd,CN))(298) = 82 +/- 2 s(-1) mol(-1) kg, DeltaH(2) (Pd,CN) = 23.5 +/- 1 kJ mol(-1), DeltaS(2) (Pd,CN) = -129 +/- 5 J mol(-1) K(-1), and DeltaV(2) (Pd,CN) = -22 +/- 2 cm(3) mol(-1). At low pH, the tetracyanopalladate is protonated (pK(a)(Pd(4,H)) = 3.0 +/- 0.3) to form [Pd(CN)(3)HCN](-). The rate law of the cyanide exchange on the protonated complex is also purely second order, with (k(2)(PdH,CN))(298) = (4.5 +/- 1.3) x 10(3) s(-1) mol(-1) kg. [Ni(CN)(4)](2-) is involved in various equilibrium reactions, such as the formation of [Ni(CN)(5)](3-), [Ni(CN)(3)HCN](-), and [Ni(CN)(2)(HCN)(2)] complexes. Our (13)C NMR measurements have allowed us to determine that the rate constant leading to the formation of [Ni(CN)(5)](3-) is k(2)(Ni(4),CN) = (2.3 +/- 0.1) x 10(6) s(-1) mol(-1) kg when the following activation parameters are used: DeltaH(2)() (Ni,CN) = 21.6 +/- 1 kJ mol(-1), DeltaS(2) (Ni,CN) = -51 +/- 7 J mol(-1) K(-1), and DeltaV(2) (Ni,CN) = -19 +/- 2 cm(3) mol(-1). The rate constant of the back reaction is k(-2)(Ni(4),CN) = 14 x 10(6) s(-1). The rate law pertaining to [Ni(CN)(2)(HCN)(2)] was found to be second order at pH 3.8, and the value of the rate constant is (k(2)(Ni(4,2H),CN))(298) = (63 +/- 15) x10(6) s(-1) mol(-1) kg when DeltaH(2) (Ni(4,2H),CN) = 47.3 +/- 1 kJ mol(-1), DeltaS(2) (Ni(4,2H),CN) = 63 +/- 3 J mol(-1) K(-1), and DeltaV(2) (Ni(4,2H),CN) = - 6 +/- 1 cm(3) mol(-1). The cyanide-exchange rate constant on [M(CN)(4)](2-) for Pt, Pd, and Ni increases in a 1:7:200 000 ratio. This trend is modified at low pH, and the palladium becomes 400 times more reactive than the platinum because of the formation of [Pd(CN)(3)HCN](-). For all cyanide exchanges on tetracyano complexes (A mechanism) and on their protonated forms (I/I(a) mechanisms), we have always observed a pure second-order rate law: first order for the complex and first order for CN(-). The nucleophilic attack by HCN or solvation by H(2)O is at least nine or six orders of magnitude slower, respectively than is nucleophilic attack by CN(-) for Pt(II), Pd(II), and Ni(II), respectively.     

Cyanide-limited complexation of molybdenum(III): synthesis of octahedral [Mo(CN)(6)](3-) and cyano-bridged [Mo(2)(CN)(11)](5-)

Octahedral coordination of molybdenum(III) is achieved by limiting the amount of cyanide available upon complex formation. Reaction of Mo(CF(3)SO(3))(3) with LiCN in DMF affords Li(3)[Mo(CN)(6)] x 6DMF (1), featuring the previously unknown octahedral complex [Mo(CN)(6)](3-). The complex exhibits a room-temperature moment of mu(eff) = 3.80 mu(B), and assignment of its absorption bands leads to the ligand field parameters Delta(o) = 24800 cm(-1) and B = 247 cm(-1). Further restricting the available cyanide in a reaction between Mo(CF(3)SO(3))(3) and (Et(4)N)CN in DMF, followed by recrystallization from DMF/MeOH, yields (Et(4)N)(5)[Mo(2)(CN)(11)] x 2DMF x 2MeOH (2). The dinuclear [Mo(2)(CN)(11)](5-) complex featured therein contains two octahedrally coordinated Mo(III) centers spanned by a bridging cyanide ligand. A fit to the magnetic susceptibility data for 2, gives J = -113 cm(-1) and g = 2.33, representing the strongest antiferromagnetic coupling yet observed through a cyanide bridge. Efforts to incorporate these new complexes in magnetic Prussian blue-type solids are ongoing.     

Synthesis and magnetic properties of 3-D [Ru(II/III)(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)] (M = Cr,Fe, Co)

Three-dimensional network structures of [Ru(II/III)(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)] (M = Cr, Fe, Co) composition have been formed and their magnetic properties characterized. [Ru(II/III)(2)(O(2)CMe)(4)](3)[M(III)(CN)(6)] (M = Cr, Fe, Co) have nu(CN) IR absorptions at 2138, 2116, and 2125 cm(-1) and have body-centered unit cells (a = 13.34, 13.30, and 13.10 A, respectively) with -M-Ctbd1;N-Ru=Ru-Ntbd1;C-M- linkages along all three Cartesian axes. [Ru(II/III)(2)(O(2)CMe)(4)](3)[Cr(III)(CN)(6)] magnetically orders as a ferrimagnet (T(c) = 33 K) and has an unusual constricted hysteresis loop.     

Record ferromagnetic exchange through cyanide and elucidation of the magnetic phase diagram for a Cu(II)Re(IV)(CN)2 chain compound

Reaction of the high-magnetic anisotropy building unit [ReCl(4)(CN)(2)](2-) with [Cu(MeCN)(6)](2+) and hydrotris(pyrazol-1-yl)borate (Tp(-)) affords the zigzag chain compound (Bu(4)N)[TpCuReCl(4)(CN)(2)]. Dc magnetic susceptibility measurements reveal the presence of ferromagnetic exchange coupling between Re(IV) and Cu(II) centers along each chain and a fit to the data gives an exchange constant of J/k(B) = +41 K (+29 cm(-1)), representing the strongest ferromagnetic coupling yet observed through cyanide. Below 11.4 K and at applied fields of less than 3600 Oe, the compound undergoes a phase transition to an antiferromagnetic ground state, stemming from weak π-π interchain interactions of strength J(⊥)/k(B) = -1.7 K (-1.2 cm(-1)). This metamagnetic behavior is fully elucidated using both experimental and theoretical methods. In addition, theoretical modeling provides a detailed determination of the local anisotropy tensors corresponding to the [ReCl(4)(CN)(2)](2-) units and demonstrates that the zigzag arrangement of the Re(IV) centers significantly reduces the effective anisotropy of the chain. These results demonstrate the utility of the Re(IV)-CN-Cu(II) linkage and the importance of anisotropic spin orientation in designing strongly coupled systems, which will aid in both the realization of single-chain magnets with higher relaxation barriers and in the construction of high-dimensional cyano-bridged materials exhibiting higher ordering temperatures.     

Fe(bipy)(CN)(4)](-) as a versatile building block for the design of heterometallic systems: synthesis, crystal structure, and magnetic properties of PPh(4)[Fe(III)(bipy)(CN)(4)] x H(2)O, [[Fe(III)(bipy)(CN)(4)](2)M(II)(H(2)O)(4)] x 4H(2)O, and [[Fe(III)(bipy)(CN)(4)](2)Zn(II)] x 2H(2)O [bipy = 2,2'-Bipyridine; M = Mn and Zn

The new cyano complexes of formulas PPh(4)[Fe(III)(bipy)(CN)(4)] x H(2)O (1), [[Fe(III)(bipy)(CN)(4)](2)M(II)(H(2)O)(4)] x 4H(2)O with M = Mn (2) and Zn (3), and [[Fe(III)(bipy)(CN)(4)](2)Zn(II)] x 2H(2)O (4) [bipy = 2,2'-bipyridine and PPh(4) = tetraphenylphosphonium cation] have been synthesized and structurally characterized. The structure of complex 1 is made up of mononuclear [Fe(bipy)(CN)(4)](-) anions, tetraphenyphosphonium cations, and water molecules of crystallization. The iron(III) is hexacoordinated with two nitrogen atoms of a chelating bipy and four carbon atoms of four terminal cyanide groups, building a distorted octahedron around the metal atom. The structure of complexes 2 and 3 consists of neutral centrosymmetric [[Fe(III)(bipy)(CN)(4)](2)M(II)(H(2)O)(4)] heterotrinuclear units and crystallization water molecules. The [Fe(bipy)(CN)(4)](-) entity of 1 is present in 2 and 3 acting as a monodentate ligand toward M(H(2)O)(4) units [M = Mn(II) (2) and Zn(II) (3)] through one cyanide group, the other three cyanides remaining terminal. Four water molecules and two cyanide nitrogen atoms from two [Fe(bipy)(CN)(4)](-) units in trans positions build a distorted octahedron surrounding Mn(II) (2) and Zn(II) (3). The structure of the [Fe(phen)(CN)(4)](-) complex ligand in 2 and 3 is close to that of the one in 1. The intramolecular Fe-M distances are 5.126(1) and 5.018(1) A in 2 and 3, respectively. 4 exhibits a neutral one-dimensional polymeric structure containing two types of [Fe(bipy)(CN)(4)](-) units acting as bismonodentate (Fe(1)) and trismonodentate (Fe(2)) ligands versus the divalent zinc cations through two cis-cyanide (Fe(1)) and three fac-cyanide (Fe(2)) groups. The environment of the iron atoms in 4 is distorted octahedral as in 1-3, whereas the zinc atom is pentacoordinated with five cyanide nitrogen atoms, describing a very distorted square pyramid. The iron-zinc separations across the single bridging cyanides are 5.013(1) and 5.142(1) A at Fe(1) and 5.028(1), 5.076(1), and 5.176(1) A at Fe(2). The magnetic properties of 1-3 have been investigated in the temperature range 2.0-300 K. 1 is a low-spin iron(III) complex with an important orbital contribution. The magnetic properties of 3 correspond to the sum of two magnetically isolated spin triplets, the antiferromagnetic coupling between the low-spin iron(III) centers through the -CN-Zn-NC- bridging skeleton (iron-iron separation larger than 10 A) being very weak. More interestingly, 2 exhibits a significant intramolecular antiferromagnetic interaction between the central spin sextet and peripheral spin doublets, leading to a low-lying spin quartet.     

Solubility, complex formation, and redox reactions in the Tl2O3-HCN/CN(-)-H2O system. Crystal structures of the cyano compounds Tl(CN)3.H2O, Na[Tl(CN)4].3H2O, K[Tl(CN)4], and Tl(I)[Tl(III)(CN)4] and of Tl(I)2C2O4

Thallium(III) oxide can be dissolved in water in the presence of strongly complexing cyanide ions. Tl(III) is leached from its oxide both by aqueous solutions of hydrogen cyanide and by alkali-metal cyanides. The dominating cyano complex of thallium(III) obtained by dissolution of Tl2O3 in HCN is [Tl(CN)3(aq)] as shown by 205Tl NMR. The Tl(CN)3 species has been selectively extracted into diethyl ether from aqueous solution with the ratio CN-/Tl(III) = 3. When aqueous solutions of the MCN (M = Na+, K+) salts are used to dissolve thallium(III) oxide, the equilibrium in liquid phase is fully shifted to the [Tl(CN)4]- complex. The Tl(CN)3 and Tl(CN)4- species have for the first time been synthesized in the solid state as Tl(CN)3.H2O (1), M[Tl(CN)4] (M = Tl (2) and K (3)), and Na[Tl(CN)4].3H2O (4) salts, and their structures have been determined by single-crystal X-ray diffraction. In the crystal structure of 1, the thallium(III) ion has a trigonal bipyramidal coordination with three cyanide ions in the equatorial plane, while an oxygen atom of the water molecule and a nitrogen atom from a cyanide ligand, attached to a neighboring thallium complex, form a linear O-Tl-N fragment. In the three compounds of the tetracyano-thallium(III) complex, 2-4, the [Tl(CN)4]- unit has a distorted tetrahedral geometry. Along with the acidic leaching (enhanced by Tl(III)-CN- complex formation), an effective reductive dissolution of the thallium(III) oxide can also take place in the Tl2O3-HCN-H2O system yielding thallium(I), while hydrogen cyanide is oxidized to cyanogen. The latter is hydrolyzed in aqueous solution giving rise to a number of products including (CONH2)2, NCO-, and NH4+ detected by 14N NMR. The crystalline compounds, Tl(I)[Tl(III)(CN)4], Tl(I)2C2O4, and (CONH2)2, have been obtained as products of the redox reactions in the system.     

Direct Lanthanide-Transition Metal Interactions: Synthesis of (NH(3))(2)YbFe(CO)(4) and Crystal Structures of {[(CH(3)CN)(3)YbFe(CO)(4)](2).CH(3)CN}(infinity) and [(CH(3)CN)(3)YbFe(CO)(4)](infinity)

The heterometallic complex (NH(3))(2)YbFe(CO)(4) was prepared from the reduction of Fe(3)(CO)(12) by Yb in liquid ammonia. Ammonia was displaced from (NH(3))(2)YbFe(CO)(4) by acetonitrile in acetonitrile solution, and the crystalline compounds {[(CH(3)CN)(3)YbFe(CO)(4))](2).CH(3)CN}(infinity) and [(CH(3)CN)(3)YbFe(CO)(4)](infinity) were obtained. An earlier X-ray study of {[(CH(3)CN)(3)YbFe(CO)(4)](2).CH(3)CN}(infinity) showed that it is a ladder polymer with direct Yb-Fe bonds. In the present study, an X-ray crystal structure analysis also showed that [(CH(3)CN)(3)YbFe(CO)(4)](infinity) is a sheetlike array with direct Yb-Fe bonds. Crystal data for {[(CH(3)CN)(3)YbFe(CO)(4)](2).CH(3)CN}(infinity): monoclinic space group P2(1)/c, a = 21.515(8) ?, b = 7.838(2) ?, c = 19.866(6) ?, beta = 105.47(2) degrees, Z = 4. Crystal data for [(CH(3)CN)(3)YbFe(CO)(4)](infinity): monoclinic space group P2(1)/n, a = 8.364(3) ?, b = 9.605(5) ?, c = 17.240(6) ?, beta = 92.22(3) degrees, Z = 4. Electrical conductivity measurements in acetonitrile show that these acetonitrile complexes are partially dissociated into ionic species. IR and NMR spectra of the solutions reveal the presence of [HFe(CO)(4)](-). However, upon recrystallization, the acetonitrile complexes show no evidence for the presence of [HFe(CO)(4)](-) on the basis of their IR spectra. The solid state MAS (2)H NMR spectra of deuterated acetonitrile complexes give no evidence for [(2)HFe(CO)(4)](-). It appears that rupture of the Yb-Fe bond could occur in solution to generate the ion pair [L(n)Yb](2+)[Fe(CO)(4)](2-), but then the highly basic [Fe(CO)(4)](2-) anion could abstract a proton from a coordinated acetonitrile ligand to form [HFe(CO)(4)](-). However, upon crystallization, the proton could be transferred back to the ligand, which results in the neutral polymeric species.     

mer-[Fe(pcq)(CN)3]-: a novel cyanide-containing building block and its application to assembling cyanide-bridged trinuclear FeIII2MnII complexes [pcq- = 8-(pyridine-2-carboxamido)quinoline anion

A new cyanide-containing building block K[Fe(pcq)(CN)(3)] [1; pcq(-) = 8-(pyridine-2-carboxamido)quinoline anion] containing a low-spin Fe(III) center with three cyanide groups in a meridional arrangement has been successfully designed and synthesized. Three cyanide-bridged trinuclear Fe(III)(2)Mn(II) complexes, [Fe(pcq)(CN)(3)](2)[Mn(CH(3)OH)(2)(H(2)O)(2)].2H(2)O (2), [Fe(pcq)(CN)(3)](2)[Mn(bipy)(2)].CH(3)OH.2H(2)O (3), and [Fe(pcq)(CN)(3)](2)[Mn(phen)(2)].CH(3)OH.2H(2)O (4), have been synthesized and structurally characterized. The magnetic susceptibilities of the three heterometallic complexes have been investigated.     

Metal Cyanide Ions Mx(CN)y]+,- in the gas phase: M = Fe,Co, Ni,Zn, Cd,Hg, Fe + Ag,Co + Ag

The generation of metal cyanide ions in the gas phase by laser ablation of M(CN)(2) (M = Co, Ni, Zn, Cd, Hg), Fe(III)[Fe(III)(CN)(6)] x xH(2)O, Ag(3)[M(CN)(6)] (M = Fe, Co), and Ag(2)[Fe(CN)(5)(NO)] has been investigated using Fourier transform ion cyclotron resonance mass spectrometry. Irradiation of Zn(CN)(2) and Cd(CN)(2) produced extensive series of anions, [Zn(n)(CN)(2n+1)](-) (1 < or = n < or = 27) and [Cd(n)(CN)(2n+1)](-) (n = 1, 2, 8-27, and possibly 29, 30). Cations Hg(CN)(+) and [Hg(2)(CN)(x)](+) (x = 1-3), and anions [Hg(CN)(x)](-) (x = 2, 3), are produced from Hg(CN)(2). Irradiation of Fe(III)[Fe(III)(CN)(6)] x xH(2)O gives the anions [Fe(CN)(2)](-), [Fe(CN)(3)](-), [Fe(2)(CN)(3)](-), [Fe(2)(CN)(4)](-), and [Fe(2)(CN)(5)](-). When Ag(3)[Fe(CN)(6)] is ablated, [AgFe(CN)(4)](-) and [Ag(2)Fe(CN)(5)](-) are observed together with homoleptic anions of Fe and Ag. The additional heterometallic complexes [AgFe(2)(CN)(6)](-), [AgFe(3)(CN)(8)](-), [Ag(2)Fe(2)(CN)(7)](-), and [Ag(3)Fe(CN)(6)](-) are observed on ablation of Ag(2)[Fe(CN)(5)(NO)]. Homoleptic anions [Co(n)(CN)(n+1)](-) (n = 1-3), [Co(n)(CN)(n+2)](-) (n = 1-3), [Co(2)(CN)(4)](-), and [Co(3)(CN)(5)](-) are formed when anhydrous Co(CN)(2) is the target. Ablation of Ag(3)[Co(CN)(6)] yields cations [Ag(n)(CN)(n-1)](+) (n = 1-4) and [Ag(n)Co(CN)(n)](+) (n = 1, 2) and anions [Ag(n)(CN)(n+1)](-) (n = 1-3), [Co(n)(CN)(n-1)](-) (n = 1, 2), [Ag(n)Co(CN)(n+2)](-) (n = 1, 2), and [Ag(n)Co(CN)(n+3)](-) (n = 0-2). The Ni(I) species [Ni(n)(CN)(n-1)](+) (n = 1-4) and [Ni(n)(CN)(n+1)](-) (n = 1-3) are produced when anhydrous Ni(CN)(2) is irradiated. In all cases, CN(-) and polyatomic carbon nitride ions C(x)N(y)(-) are formed concurrently. On the basis of density functional calculations, probable structures are proposed for most of the newly observed species. General structural features are low coordination numbers, regular trigonal coordination stereochemistry for d(10) metals but distorted trigonal stereochemistry for transition metals, the occurrence of M-CN-M and M(-CN-)(2)M bridges, addition of AgCN to terminal CN ligands, and the occurrence of high spin ground states for linear [M(n)(CN)(n+1)](-) complexes of Co and Ni.     

Syntheses and structural characterizations of sheet- and column-like lanthanide-transition metal arrays: the effect of hydrogen bonding on the structure when K(+) is replaced by [NH4]+

Sheet- and column-like cyanide bridged lanthanide-transition metal arrays were synthesized through metathesis reactions between anhydrous LnCl(3) (Ln = Eu, Yb) and A(2)[M(CN)(4)] (A = K(+), NH(4)(+); M = Ni, Pt) in a 1:2 molar ratio in DMF (DMF = N,N-dimethylformamide) solution. Single-crystal X-ray analysis revealed that complexes of formula [K(DMF)(7)Ln[M(CN)(4)](2)](infinity) (Ln = Eu, M = Ni, 1; Ln = Yb, M = Pt, 2) consist of infinite layers of neutral, puckered sheets that contain hexagonal rings of composition [(DMF)(10)Ln(2)[M(CN)(4)](3)](6) with interstitial (DMF)(4)K(2)[M(CN)(4)] units located between the layers. The sheet structure is generated through the repeating (DMF)(10)Ln(2)[M(CN)(4)](3) unit with trans cyanide ligands in [M(CN)(4)](2)(-) serving as bridges. The column-like complex [(NH(4))(DMF)(4)Yb[Pt(CN)(4)](2)](infinity), 3, is formed when NH(4)(+) replaces K(+). It consists of infinite, negatively charged, square, parallel columns bundled through N-H...NC hydrogen bonds between NH(4)(+) and terminal CN from the columns. Cis cyanide ligands in [Pt(CN)(4)](2)(-) units serve as bridges. Complex 3 is the first known example where Ln(III) centers are coordinated to four [M(CN)(4)](2)(-) units. Bicapped (square face) trigonal prismatic coordination geometries were observed for Ln(III) centers in 1 and 2. Square antiprismatic geometry for Yb(III) centers are observed in 3. Crystal data for 1: triclinic space group P1, a = 8.797(2) A, b = 15.621(3) A, c = 17.973(6) A, alpha = 105.48(2) degrees, beta = 98.60(2) degrees, gamma = 98.15(2) degrees, Z = 2. Crystal data for 2: triclinic space group P1, a = 8.825(1) A, b = 15.673(1) A, c = 17.946(1) A, alpha = 105.46(2) degrees, beta = 99.10(1) degrees, gamma = 98.59(1) degrees, Z = 2. Crystal data for 3: monoclinic space group P2(1)/c, a = 9.032(1) A, b = 29.062(1) A, c = 15.316(1) A, beta = 94.51(1) degrees, Z = 2.     

Modification of binuclear Pt-Tl bonded complexes by attaching bipyridine ligands to the thallium site

Complex formation of monomeric thallium(III) species with 2,2'-bipyridine (bipy) in dimethyl sulfoxide (dmso) and acetonitrile solutions was studied by means of multinuclear ((1)H, (13)C, and (205)Tl) NMR spectroscopy. For the first time, NMR signals of the individual species [Tl(bipy)(m)(solv)](3+) (m = 1-3) were observed despite intensive ligand and solvent exchange processes. The tris(bipy) complex was crystallized as [Tl(bipy)(3)(dmso)](ClO(4))(3)(dmso)(2) (1), and its crystal structure determined. In this compound, thallium is seven-coordinated; it is bonded to six nitrogen atoms of the three bipy molecules and to an oxygen atom of dmso. Metal-metal bonded binuclear complexes [(NC)(5)Pt-Tl(CN)(n)(solv)](n)(-) (n = 0-3) have been modified by attaching bipy molecules to the thallium atom. A reaction between [(NC)(5)Pt-Tl(dmso)(4)](s) and 2,2'-bipyridine in dimethyl sulfoxide solution results in the formation of a new complex, [(NC)(5)Pt-Tl(bipy)(solv)]. The presence of a direct Pt-Tl bond in the complex is convincingly confirmed by a very strong one-bond (195)Pt-(205)Tl spin-spin coupling ((1)J((195)Pt-(205)Tl) = 64.9 kHz) detected in both (195)Pt and (205)Tl NMR spectra. In solutions containing free cyanide, coordination of CN(-) to the thallium atom occurs, and the complex [(NC)(5)Pt-Tl(bipy)(CN)(solv)](-) ((1)J((195)Pt-(205)Tl) = 50.1 kHz) is formed as well. Two metal-metal bonded compounds containing bipy as a ligand were crystallized and their structures determined by X-ray diffractometry: [(NC)(5)Pt-Tl(bipy)(dmso)(3)] (2) and [(NC)(5)Pt-Tl(bipy)(2)] (3). The Pt-Tl bonding distances in the compounds, 2.6187(7) and 2.6117(5) A, respectively, are among the shortest reported separations between these two metals. The corresponding force constants in the molecules, 1.38 and 1.68 N/cm, respectively, were calculated using Raman stretching frequencies of the Pt-Tl vibrations and are characteristic for a single metal-metal bond. Electronic absorption spectra were recorded for the [(NC)(5)Pt-Tl(bipy)(m)(solv)] compounds, and the optical transition was attributed to the metal-metal bond assigned.     

Kinetics of the reactions between [S(2)MoS(2)Cu(SC(6)H(4)R-4)](2-)(R = MeO, H, Cl or NO(2)) and CN(-): substitution mechanism at a 3-coordinate Cu(I) site

The kinetics of the reaction between [S(2)MoS(2)Cu(SC(6)H(4)R-4)](2-)(R = MeO, H, Cl or NO(2)) and CN(-) to form [S(2)MoS(2)CuCN](2-) have been studied in MeCN using stopped-flow spectrophotometry. In all cases, the rate law is of the form, Rate ={k+k(2)(R)[CN(-)]}[S(2)MoS(2)Cu(SC(6)H(4)R-4)(2-)]. It is proposed that both k and k correspond to associative substitution mechanisms. The k pathway involves attack by CN(-) at the copper site followed by dissociation of the thiolate. The k pathway involves attack of the solvent (MeCN) at the copper site, followed by dissociation of the thiolate to form [S(2)MoS(2)Cu(NCMe)](-). Subsequent rapid substitution of the coordinated solvent by cyanide produces [S(2)MoS(2)CuCN](2-). The evidence that both the k and k pathways involve associative mechanisms are: (i) the 4-R-substituent on the thiolate ligand has a similar effect on both k and k, with electron-withdrawing 4-R-substituents facilitating substitution; (ii) both the k and k pathways are associated with similar activation parameters (for k(1)(H): DeltaH++ = 5.5 +/- 0.5 kcal mol(-1), DeltaS++ = -23.9 +/- 2.0 cal deg(-1) mol(-1); for k(2)(H): DeltaH++ = 2.3 +/- 0.5 kcal mol(-1), DeltaS++ = - 23.9 +/- 2.0 cal deg(-1) mol(-1)) and (iii) addition of C(6)H(5)S(-) results in a similar increase in both k and k.     

Hybrid cluster-cages formed via cyanometalate condensation: Cs subset Co(4)Ru(6)S(2)(CN)(12), Co(4)Ru(9)S(6)(CN)(9), and Rh(4)Ru(9)S(6)(CN)(9) frameworks

Condensation of cyanometalates and cluster building blocks leads to the formation of hybrid molecular cyanometalate cages. Specifically, the reaction of [Cs subset [CpCo(CN)(3)](4)[CpRu](3)] and [(cymene)(2)Ru(3)S(2)(NCMe)(3)]PF(6) produced [Cs subset [CpCo(CN)(3)](4)[(cymene)(2)Ru(3)S(2)][CpRu](3)](PF(6))(2), Cs subset Co(4)Ru(6)S(2)(2+). Single-crystal X-ray diffraction, NMR spectroscopy, and ESI-MS measurements show that Cs subset Co(4)Ru(6)S(2)(2+ ) consists of a Ru(4)Co(4)(CN)(12) box fused with a Ru(3)S(2) cluster via a common Ru atom. The reaction of PPN[CpCo(CN)(3)] and 0.75 equiv of [(cymene)(2)(MeCN)(3)Ru(3)S(2)](PF(6))(2) in MeCN solution produced [[CpCo(CN)(3)](4)[(cymene)(2)Ru(3)S(2)](3)](PF(6))(2), Co(4)Ru(9)S(6)(2+). Crystallographic analysis, together with NMR and ESI-MS measurements, shows that Co(4)Ru(9)S(6)(2+ ) consists of a Ru(3)Co(4)(CN)(9) "defect box" core, wherein each Ru is fused to a Ru(3)S(2) clusters. The analogous condensation using [CpRh(CN)(3)](-) in place of [CpCo(CN)(3)](-) produced the related cluster-cage Rh(4)Ru(9)S(6)(2+). Electrochemical analyses of both Co(4)Ru(9)S(6)(2+) and Rh(4)Ru(9)S(6)(2+) can be rationalized in the context of reduction at the cluster and the Co(III) subunits, the latter being affected by the presence of alkali metal cations.     

Catalytic and direct oxidation of cysteine by octacyanomolybdate(V)

The oxidation of cysteine by [Mo(CN)(8)](3-) in deoxygenated aqueous solution at a moderate pH is strongly catalyzed by Cu(2+), to the degree that impurity levels of Cu(2+) are sufficient to dominate the reaction. Dipicolinic acid (dipic) is a very effective inhibitor of this catalysis, such that with 1 mM dipic, the direct oxidation can be studied. UV-vis spectra and electrochemistry show that [Mo(CN)(8)](4-) is the Mo-containing product. Cystine and cysteinesulfinate are the predominant cysteine oxidation products. The stoichiometric ratio (Deltan(Mo(V))/Deltan(cysteine)) of 1.4 at pH 10.8 is consistent with this product distribution. At pH 1.5, the reaction is quite slow and yields intractable kinetics. At pH 4.5, the rates are much faster and deviate only slightly from pseudo-first-order behavior. With 2 mM PBN (N-phenyl-tert-butyl nitrone) present at pH 4.5, the reaction rate is about 20% less and shows excellent pseudo-first-order behavior, but the stoichiometric ratio is not significantly changed. The rates also display a significant specific cation effect. In the presence of spin-trap PBN, the kinetics were studied over the pH range 3.48-12.28, with [Na(+)] maintained at 0.09-0.10 M. The rate law is -d[Mo(V)]/dt = k[cysteine](tot)[Mo(V)], with k = {2(k(b)K(a1)K(a2)[H(+)] + k(c)K(a1)K(a2)K(a3))}/([H(+)](3) + K(a1)[H(+)](2) + K(a1)K(a2)[H(+)] + K(a1)K(a2)K(a3)), where K(a1), K(a2), and K(a3) are the successive acid dissociation constants of HSCH(2)CH(NH(3)(+))CO(2)H. Least-squares fitting yields k(b) = (7.1 +/- 0.4) x 10(4) M(-1) s(-1) and k(c) = (2.3 +/-0.2) x 10(4) M(-1) s(-1) at mu = 0.1 M (NaCF(3)SO(3)) and 25 degrees C. A mechanism is inferred in which k(b) and k(c) correspond to electron transfer to Mo(V) from the thiolate forms of anionic and dianionic cysteine.     

Nickel(II)-molybdenum(III)-cyanide clusters: synthesis and magnetic behavior of species incorporating [(Me(3)tacn)Mo(CN)(3)

The substitution of Mo(III) for Cr(III) in metal-cyanide clusters is demonstrated as an effective means of increasing the strength of the magnetic exchange coupling and introducing magnetic anisotropy. Synthesis of the octahedral complex [(Me(3)tacn)Mo(CN)(3)] (Me(3)tacn = N,N',N"-trimethyl-1,4,7-triazacyclononane) is accomplished with the addition of precisely 3 equiv of LiCN to a solution of [(Me(3)tacn)Mo(CF(3)SO(3))(3)] in DMF. An excess of LiCN prompts formation of a seven-coordinate complex, [(Me(3)tacn)Mo(CN)(4)](1)(-), whereas less LiCN produces multinuclear species such as [(Me(3)tacn)(2)Mo(2)(CN)(5)](1+). In close parallel to reactions previously performed with [(Me(3)tacn)Cr(CN)(3)], assembly reactions between [(Me(3)tacn)Mo(CN)(3)] and [Ni(H(2)O)(6)](2+) or [(cyclam)Ni(H(2)O)(2)](2+) (cyclam = 1,4,8,11-tetraazacyclotetradecane) afford face-centered cubic [(Me(3)tacn)(8)Mo(8)Ni(6)(CN)(24)](12+) and linear [(Me(3)tacn)(2)(cyclam)NiMo(2)(CN)(6)](2+) clusters, respectively. Generation of the former involves a thermally induced cyanide linkage isomerization, which rapidly leads to a low-spin form of the cluster containing diamagnetic Ni(II) centers. The cyclic voltammagram of this species in DMF reveals a sequence of six successive reduction waves spaced approximately 130 mV apart, suggesting class II mixed-valence behavior upon reduction. The magnetic properties of the aforementioned linear cluster are consistent with the expected ferromagnetic coupling and an S = 4 ground state, but otherwise vary slightly with the specific conformation adopted (as influenced by the packing of associated counteranions and solvate molecules in the crystal). Magnetization data indicate an axial zero-field splitting parameter with a magnitude falling in the range [D] = 0.44-0.72 cm(-1), and fits to the magnetic susceptibility data yield exchange coupling constants in the range J = 17.0-17.6 cm(-1). These values represent significant increases over those displayed by the analogous Cr(III)-containing cluster. When perchlorate is used as a counteranion, [(Me(3)tacn)(2)(cyclam)NiMo(2)(CN)(6)](2+) crystallizes from water in a dimeric form with pairs of the linear clusters directly linked via hydrogen bonding. In this case, fitting the magnetic susceptibility data requires use of two coupling constants: one intramolecular with J = 14.9 cm(-1) and another intermolecular with J' = -1.9 cm(-1). Reacting [(Me(3)tacn)Mo(CN)(3)] with a large excess of [(cyclam)Ni(H(2)O)(2)](2+) produces a [(Me(3)tacn)(2)(cyclam)(3)(H(2)O)(2)Ni(3)Mo(2)(CN)(6)](6+) cluster possessing a zigzag structure that is a simple extension of the linear cluster geometry. Its magnetic behavior is consistent with weaker ferromagnetic coupling and an S = 6 ground state. Similar reactions employing an equimolar ratio of reactants afford related one-dimensional chains of formula [(Me(3)tacn)(cyclam)NiMo(CN)(3)](2+). Once again, the ensuing structure depends on the associated counteranions, and the magnetic behavior indicates ferromagnetic coupling. It is hoped that substitutions of the type exemplified here will be of utility in the design of new single-molecule magnets.     

Syntheses, structures, and magnetic properties of low-dimensional heterometallic complexes based on the versatile building block [(Tp)Cr(CN)3]-

Using the tricyano precursor (Bu(4)N)[(Tp)Cr(CN)(3)] (Bu(4)N(+) = tetrabutylammonium cation; Tp = tris(pyrazolyl)hydroborate), a pentanuclear heterometallic cluster [(Tp)(2)Cr(2)(CN)(6)Cu(3)(Me(3)tacn)(3)][(Tp)Cr(CN)(3)](ClO(4))(3)·5H(2)O (1, Me(3)tacn = N,N',N'-trimethyl-1,4,7-triazacyclononane), three tetranuclear heterometallic clusters [(Tp)(2)Cr(2)(CN)(6)Cu(2)(L(OEt))(2)]·2.5CH(3)CN (2, L(OEt) = [(Cp)Co(P(O)(OEt)(2))(3)], Cp = cyclopentadiene), [(Tp)(2)Cr(2)(CN)(6)Mn(2)(L(OEt))(2)]·4H(2)O (3), and [(Tp)(2)Cr(2)(CN)(6)Mn(2)(phen)(4)](ClO(4))(2) (4, phen = phenanthroline), and a one-dimensional (1D) chain polymer [(Tp)(2)Cr(2)(CN)(6)Mn(bpy)](n) (5, bpy = 2,2'-bipyridine) have been synthesized and structurally characterized. Complex 1 shows a trigonal bipyramidal geometry in which [(Tp)Cr(CN)(3)](-) units occupy the apical positions and are linked through cyanide to [Cu(Me(3)tacn)](2+) units situated in the equatorial plane. Complexes 2-4 show similar square structures, where Cr(III) and M(II) (M = Cu(II) or Mn(II)) ions are alternatively located on the rectangle corners. Complex 5 consists of a 4,2-ribbon-like bimetallic chain. Ferromagnetic interactions between Cr(III) and Cu(II) ions bridged by cyanides are observed in complexes 1 and 2. Antiferromagnetic interactions are presented between Cr(III) and Mn(II) ions bridged by cyanides in complexes 3-5. Complex 5 shows metamagnetic behavior with a critical field of about 22.5 kOe at 1.8 K.     

Cyanation of aryl bromides with K4[Fe(CN)6] catalyzed by dichloro[bis{1-(dicyclohexylphosphanyl)piperidine}]palladium, a molecular source of nanoparticles, and the reactions involved in the catalyst-deactivation processes

Dichloro[bis{1-(dicyclohexylphosphanyl)piperidine}]palladium [(P{(NC(5)H(10))(C(6)H(11))(2)})(2)PdCl(2)] (1) is a highly active and generally applicable C-C cross-coupling catalyst. Apart from its high catalytic activity in Suzuki, Heck, and Negishi reactions, compound 1 also efficiently converted various electronically activated, nonactivated, and deactivated aryl bromides, which may contain fluoride atoms, trifluoromethane groups, nitriles, acetals, ketones, aldehydes, ethers, esters, amides, as well as heterocyclic aryl bromides, such as pyridines and their derivatives, or thiophenes into their respective aromatic nitriles with K(4)[Fe(CN)(6)] as a cyanating agent within 24 h in NMP at 140 °C in the presence of only 0.05 mol % catalyst. Catalyst-deactivation processes showed that excess cyanide efficiently affected the molecular mechanisms as well as inhibited the catalysis when nanoparticles were involved, owing to the formation of inactive cyanide complexes, such as [Pd(CN)(4)](2-), [(CN)(3)Pd(H)](2-), and [(CN)(3)Pd(Ar)](2-). Thus, the choice of cyanating agent is crucial for the success of the reaction because there is a sharp balance between the rate of cyanide production, efficient product formation, and catalyst poisoning. For example, whereas no product formation was obtained when cyanation reactions were examined with Zn(CN)(2) as the cyanating agent, aromatic nitriles were smoothly formed when hexacyanoferrate(II) was used instead. The reason for this striking difference in reactivity was due to the higher stability of hexacyanoferrate(II), which led to a lower rate of cyanide production, and hence, prevented catalyst-deactivation processes. This pathway was confirmed by the colorimetric detection of cyanides: whereas the conversion of β-solvato-α-cyanocobyrinic acid heptamethyl ester into dicyanocobyrinic acid heptamethyl ester indicated that the cyanide production of Zn(CN)(2) proceeded at 25 °C in NMP, reaction temperatures of >100 °C were required for cyanide production with K(4)[Fe(CN)(6)]. Mechanistic investigations demonstrate that palladium nanoparticles were the catalytically active form of compound 1.     

Oxidation of thioglycolate by [Os(phen)3]3+: an unusual example of redox-mediated aromatic substitution

The aqueous oxidation of thioglycolic acid (TGA) by [Os(phen)(3)](3+) (phen = 1,10-phenanthroline) is catalyzed by traces of ubiquitous Cu(2+) and inhibited by the product [Os(phen)(3)](2+). In the presence of dipicolinic acid (dipic), which thoroughly masks trace Cu(2+) catalysis, and spin trap PBN, the kinetics under anaerobic conditions have been studied in the pH range 1.82-7.32. The rate law is -d[Os(phen)(3)(3+)]/dt = k[TGA](tot)[Os(phen)(3)(3+)], with k = 2{(k(b)K(a1) + k(c)K(a1)K(i))[H(+)] + k(d)K(a1)K(a2)}/{[H(+)](2) + K(a1)[H(+)] + K(a1)K(a2)}; K(a1) and K(a2) are the successive acid dissociation constants of TGA, and K(i) is the tautomerization constant of two TGA monoanions. k(b) + k(c)K(i) = (5.9 +/- 0.3) x 10(3) M(-)(1) s(-)(1), k(d) = (1.6 +/- 0.1) x 10(9) M(-)(1) s(-)(1) at mu = 0.1 M (NaCF(3)SO(3)) and 25 degrees C. The major products in the absence of spin traps are dithiodiglycolic acid, [Os(phen)(3)](2+), and [Os(phen)(2)(phen-tga)](2+), where phen-tga is phenanthroline with a TGA substituent. A mechanism is proposed in which neutral TGA is unreactive, the (minor) thiolate form of the TGA monoanion undergoes one-electron oxidation by [Os(phen)(3)](3+) (k(c)), and the dianion of TGA likewise undergoes one-electron oxidation by [Os(phen)(3)](3+) (k(d)). The Marcus cross relationship provides a good account for the magnitude of k(d) in this and related reactions of TGA. [Os(phen)(2)(phen-tga)](2+) is suggested to arise from a post-rate-limiting step involving attack of the TGA(*) radical on [Os(phen)(3)](3+).