Au(CN)4]- as a supramolecular building block for heterobimetallic coordination polymers

A series of the first coordination polymers using the [Au(CN)(4)](-) anion as a building block has been prepared. The planar tetracyanoaurate anion uses one, two, or four cyano groups to bridge to Ni(II) or Cu(II) centers and exhibits weak Au(III)-N(cyano) interactions between anions. Ni(en)(2)[Au(CN)(4)](2).H(2)O (1, en = ethylenediamine) is a molecular compound with the two [Au(CN)(4)](-) anions coordinating in a trans orientation to Ni(II) without further cyanide coordination. Cu(dien)[Au(CN)(4)](2) (2, dien = diethylenetriamine) forms a similar molecular complex; however, the dimensionality is increased through weak intermolecular Au-N(cyano) interactions of 3.002(14) A to form a 1-D zigzag chain. Cu(en)(2)[Au(CN)(4)](2) (3) also forms a molecular complex similar to 1, but with elongated axial bonds. The complex further aggregates through Au-N(cyano) interactions of 3.035(8) A to form a 2-D array. In [Cu(dmeda)(2)Au(CN)(4)][Au(CN)(4)] (4, dmeda = N,N-dimethylethylenediamine) one [Au(CN)(4)](-) anion coordinates via two cis-N(cyano) donors to the axial sites of two Cu(II) centers to form a 1-D zigzag chain of alternating [Cu(dmeda)(2)](2+) and [Au(CN)(2)](-) units; the other [Au(CN)(4)](-) anion forms a 1-D chain via Au-N(cyano) interactions. In [Cu(bipy)(H(2)O)(2)(Au(CN)(4))(0.5)][Au(CN)(4)](1.5) (5, bipy = 2,2'-bipyridine) one [Au(CN)(4)](-) anion uses all four cyano moieties to bridge four different Cu(II) centers, creating a 1-D chain.     

Metal-metal interactions in platinum(II)/gold(I) or platinum(II)/silver(I) salts containing planar cations and linear anions

The salts [Pt{C(NHMe)(2)}(4)][Au(CN)(2)](2), [Pt{C(NHMe)(2)}(4)][Ag(2)(CN)(3)][Ag(CN)(2)], [Pt(en)(2)][Au(CN)(2)](2), [Pt(en)(2)][Ag(CN)(2)](2), and [Pt(bipy)(2)][Au(CN)(2)](2) have been prepared by mixing solutions of salts containing the appropriate cation with solutions of K[Au(CN)(2)] or K[Ag(CN)(2)]. Because the platinum atom in the cation is sterically protected, the structures of [Pt{C(NHMe)(2)}(4)][Au(CN)(2)](2) and [Pt{C(NHMe)(2)}(4)][Ag(2)(CN)(3)][Ag(CN)(2)] reveal no close metal-metal interactions. Colorless crystals of [Pt(en)(2)][Au(CN)(2)](2) and [Pt(en)(2)][Ag(CN)(2)](2) are isostructural and involve extended chains of alternating cations and anions that run parallel to the crystallographic a axis, along with isolated anions. In the chains, the metal-metal separations are relatively short: Pt...Au, 3.1799(3) Angstroms; Pt...Ag, 3.1949(2) Angstroms. In [Pt(bipy)(2)][Au(CN)(2)](2), each cation has axial interactions with the anions through close Pt...Au contacts [3.1735(6) Angstroms]. In addition, the anions are weakly linked through Au...Au contacts of 3.5978(9) Angstroms. Unlike the previously reported Pt/Au complex [Pt(NH(3))(4)][Au(CN)(2)](2).1.5H(2)O, which is luminescent, none of the salts reported here luminesce.     

A charge-transfer-induced spin transition in a discrete complex: the role of extrinsic factors in stabilizing three electronic isomeric forms of a cyanide-bridged co/fe cluster

A series of bimetallic, trigonal bipyramidal clusters of type {[Co(N-N)(2)](3)[Fe(CN)(6)](2)} are reported. The reaction of {Co(tmphen)(2)}(2+) with [Fe(CN)(6)](3)(-) in MeCN affords {[Co(tmphen)(2)](3)[Fe(CN)(6)](2)} (1). The cluster can exist in three different solid-state phases: a red crystalline phase, a blue solid phase obtained by exposure of the red crystals to moisture, and a red solid phase obtained by desolvation of the blue solid phase in vacuo. The properties of cluster 1 are extremely sensitive to both temperature and solvent content in each of these phases. Variable-temperature X-ray crystallography; (57)Fe Mossbauer, vibrational, and optical spectroscopies; and magnetochemical studies were used to study the three phases of 1 and related compounds, Na{[Co(tmphen)(2)](3)[Fe(CN)(6)](2)}(ClO(4))(2) (2), {[Co(bpy)(2)](3)[Fe(CN)(6)](2)}[Fe(CN)(6)](1/3) (3), and {[Ni(tmphen)(2)](3)[Fe(CN)(6)](2)} (4). The combined structural and spectroscopic investigation of 1-4 leads to the unambiguous conclusion that 1 can exist in different electronic isomeric forms, {Co(III)(2)Co(II)Fe(II)(2)} (1A), {Co(III)Co(II)(2)Fe(III)Fe(II)} (1B), and {Co(II)(3)Fe(III)(2)} (1C), and that it can undergo a charge-transfer-induced spin transition (CTIST). This is the first time that such a phenomenon has been observed for a Co/Fe molecule.     

A new basic motif in cyanometallate coordination polymers: structure and magnetic behavior of M(mu-OH2)2[Au(CN)2]2 (M=Cu, Ni)

The structures of two cyanoaurate-based coordination polymers, M(mu-OH(2))(2)[Au(CN)(2)](2) (M=Cu, Ni), were determined by using a combination of powder and single-crystal X-ray diffraction techniques. The basic structural motif for both polymers contains rarely observed M(mu-OH(2))(2)M double aqua-bridges, which generate an infinite chain; two trans [Au(CN)(2)](-) units also dangle from each metal center. The chains form ribbons that interact three dimensionally through CNH hydrogen bonding. The magnetic properties of both compounds and of the dehydrated analogue Cu[Au(CN)(2)](2) were investigated by direct current (dc) and alternating current (ac) magnetometry; muon spin-relaxation data was also obtained to probe their magnetic properties in zero-field. In M(mu-OH(2))(2)[Au(CN)(2)](2), ferromagnetic chains of M(mu-OH(2))(2)M are present below 20 K. Interchain magnetic interactions mediated through hydrogen bonding, involving water and cyanoaurate units, yield a long-range magnetically ordered system in Cu(mu-OH(2))(2)[Au(CN)(2)](2) below 0.20 K, as indicated by precession in the muon spin polarization decay. Ni(mu-OH(2))(2)[Au(CN)(2)](2) undergoes a transition to a spin-glass state in zero-field at 3.6 K, as indicated by a combination of muon spin-relaxation and ac-susceptibility data. This transition is probably due to competing interactions that lead to spin frustration. A phase transition to a paramagnetic state is possible for Ni(mu-OH(2))(2)[Au(CN)(2)](2) upon application of an external field; the critical field was determined to be 700 Oe at 1.8 K. The dehydrated compound Cu[Au(CN)(2)](2) shows weak antiferromagnetic interactions at low temperatures.     

Thermally triggered reductive elimination of bromine from Au(III) as a path to Au(I)-based coordination polymers

Four new [AuBr(2)(CN)(2)](-)-based coordination polymers, Zn(pyz)(NCMe)(2)[AuBr(2)(CN)(2)](2) (1; pyz = pyrazine), Co(pyz)[AuBr(2)(CN)(2)](2)·H(2)O (2) and [M(bipy)(2)(AuBr(2)(CN)(2))][(n)Bu(4)N][AuBr(2)(CN)(2)](2) (bipy = 4,4'-bipyridine), where M = Co (5) and Zn (6), were synthesized and three of them structurally characterized. 1 forms 1-D chains connected by pyz ligands while isostructural 5 and 6 form 3-D frameworks via [AuBr(2)(CN)(2)](-) and bipy linkers. Aqueous suspensions of 2, 5 and 6 or their precursors in situ (preferred) were heated hydrothermally to 125 °C, triggering the reductive elimination of bromine from the Au(III) centres, which yielded the [Au(CN)(2)](-)-based coordination polymers M(pyz)[Au(CN)(2)](2), where M = Zn (3) or Co (4) and Zn(bipy)[Au(CN)(2)][Au{Br(0.68)(CN)(0.32)}CN] (7), or a mixture of cyanoaurate(I)-containing products in the case of 5 and 6. The structural characterization of 3 revealed a [Au(CN)(2)](-)/pyz-based framework similar to previously reported Cu(pyz)[Au(CN)(2)](2), whereas 7 formed an intricate network consisting of individual 2-D networks held together by AuAu interactions and featuring the rare [AuBrCN](-) unit. The kinetics of the thermally-induced reductive elimination of Br(2) from K[AuBr(2)(CN)(2)] in 1-BuOH yielded a t(?) of approx. 10 min to 4 h from 98 to 68 °C, and activation parameters of ΔH(?) = 131(15) kJ mol(-1) and ΔS(?) = 14.97(4) kJ K(-1)mol(-1), indicating that the elimination of the halogen provides the highest barrier to activation.     

Tunable photoluminescence of closed-shell heterobimetallic Au-Ag dicyanide layered systems

The excited-state properties of the layered La[Ag(CN)(2)](3) and La[Au(CN)(2)](3) systems have been examined and compared with mixed-metal systems of varying metal ratios such as La[Ag(0.78)Au(0.22)(CN)(2)](3), La[Ag(0.55)Au(0.45)(CN)(2)](3), La[Ag(0.33)Au(0.67)(CN)(2)](3), and La[Ag(0.19)Au(0.81)(CN)(2)](3). We have found that these mixed-metal systems luminesce quite strongly at room temperature at an energy that is tunable and depends on the Au:Ag stoichiometric ratio. The emission energy of the mixed-metal samples lies between those of the pure Au and Ag systems. This provides evidence that the excited states responsible for this emission are delocalized over the Ag and Au centers. The strong luminescence of the mixed-metal systems at ambient temperatures is in stark contrast to the weak luminescence behavior of pure La[Au(CN)(2)](3) and La[Ag(CN)(2)](3) samples, which makes the mixed-metal systems more viable than the pure systems for practical applications.     

New structural features of unsupported chains of metal ions in luminescent [(NH3)4Pt][Au(CN)2]2 x 1.5(H2O) and related salts

Luminescent [(NH(3))(4)Pt][Au(CN)(2)](2).1.5(H(2)O), which forms from aqueous solutions of [(NH(3))(4)Pt]Cl(2) and K[Au(CN)(2)], crystallizes with extended chains of the two ions with multiple close Pt...Au (3.2804(4) and 3.2794(4) A) and Au...Au (3.2902(5), 3.3312(5), and 3.1902(4) A) contacts. Nonluminescent [(NH(3))(4)Pt][Ag(CN)(2)](2).1.4(H(2)O) is isostructural with [(NH(3))(4)Pt][Au(CN)(2)](2).1.5(H(2)O). Treatment of [(NH(3))(6)Ni]Cl(2) with K[Au(CN)(2)] forms [(NH(3))(2)Ni][Au(CN)(2)](2) in which the [Au(CN)(2)](-) ions function as nitrile ligands toward nickel, which assumes a six-coordinate structure with trans NH(3) ligands. The [Au(CN)(2)](-) ions self-associate into linear columns with close Au...Au contacts of 3.0830(5) A, and pairs of gold ions in these chains make additional but longer (3.4246(5) A) contacts with other gold ions.     

Interplay between covalent and aurophilic interactions in a series of isostructural 3D Hoffman-like frameworks containing bipyrimidine and dicyanoaurate bridges. X-Ray structure and magnetic properties of {(mu-Au(CN)(2)](2)[(M(NH(3))(2))(2)(mu-bpym)]}[Au(CN)(2)](2) (M = Ni(II), Co(II) and Cu(II))

The isomorphous coordination polymers {micro-Au(CN)(2)](2)[(M(NH(3))(2))(2)(mu-bpym)]}[Au(CN)(2)](2) (M = Co(II) (1), Ni(II) (2), Cu(II) (3)) have been prepared from the reaction of 2 equiv. M(NO(3))(2) x nH(2)O (M = Cu(II), n = 3; M = Ni(II) and Co(II), n = 6) with 1 equiv. of bipyrimidine (bpym) in aqueous ammonia and then with an aqueous solution containing 1 equiv. of K[Au(CN)(2)]. The structures of these complexes are made of bpym bridged centrosymmetric dinuclear [M(NH(3))(2)(mu-bpym)M(NH(3))(2)] units connected by [Au(CN)(2)](-) anions to four other dinuclear units giving rise to a cationic 2D (4,4) rectangular grid network, its charge being balanced by two non-coordinated [Au(CN)(2)](-). The layers are stacked in such a way that the ammonia coordinated molecules are interdigitated and aligned above and below one sheet with cavities in neighbouring sheets, giving rise to an ABAB[dot dot dot] repeat pattern of layers. Gold atoms of bridging and non-bridging dicyanoaurate anions are involved in short aurophilic interactions (Au1-Au2 distances in the range 3.12-3.14 Angstrom), leading to a chain of gold atoms running along the a direction. Neighbouring gold chains are further connected by weaker aurophilic interactions (Au1-Au1 distances in the range 3.43-3.49 Angstrom), affording a honeycomb-like 2D network of gold atoms. The (4,4) rectangular sheets and (6,3) honeycomb sheets share the Au2 atoms, leading to a unique 3D network. Magnetic measurements clearly show the existence of antiferromagnetic exchange coupling between the metal ions with susceptibility maxima at 17 K (1), 22 K (2), and 17 K (3). The data of 1 were analyzed through a full Hamiltonian involving spin-orbit coupling, axial distortion, Zeeman interactions and magnetic exchange coupling between Co(II), and the best fit gives J = -9.23 cm(-1), kappa = 0.99, lambda = -142 cm(-1), Delta = -562 cm(-1). For 2 and 3, magnetic data were fitted to the theoretical equations derived from the isotropic Hamiltonian: H = -JS(1)S(2). The best fit parameters were g = 2.050(1), J = -17.51(1) and P = 0.01(2) for 2 and g = 2.068(5), J = -20.07(8) and P = 0.015(4) for 3, respectively (P takes into account the amount of paramagnetic impurity). In order to explain the weak magnetic interaction between copper(II) ions mediated by the bipyrimidine bridging ligand in 3, we have carried out electronic structure calculations based on the density functional theory (DFT).     

Heterobimetallic coordination polymers incorporating [M(CN)(2)](-) (M = Cu,Ag) and [Ag(2)(CN)(3)](-) units: increasing structural dimensionality via M-M' and M...NC interactions

A series of new heterometallic coordination polymers has been prepared from the reaction of metal-ligand cations and KAg(CN)(2) units. Many of these contain silver-silver (argentophilic) interactions, analogous to gold-gold interactions, which serve to increase supramolecular structural dimensionality. Compared to [Au(CN)(2)](-) analogues, these polymers display new trends specific to [Ag(CN)(2)](-), including the formation of [Ag(2)(CN)(3)](-) and the presence of Ag...N interactions. [Cu(en)(2)][Ag(2)(CN)(3)][Ag(CN)(2)] (1, en = ethylenediamine) forms 1-D chains of alternating [Ag(CN)(2)](-) and [Ag(2)(CN)(3)](-) units via argentophilic interactions of 3.102(1) A. These chains are connected into a 2-D array by strong cyano(N)-Ag interactions of 2.572(3) A. [Cu(dien)Ag(CN)(2)](2)[Ag(2)(CN)(3)][Ag(CN)(2)] (2, dien = diethylenetriamine) forms a 1-D chain of alternating [Cu(dien)](2+) and [Ag(CN)(2)](-) ions with the Cu(II) atoms connected in an apical/equatorial fashion. These chains are cross-linked by [Ag(2)(CN)(3)](-) units via argentophilic interactions of 3.1718(8) A and held weakly in a 3-D array by argentophilic interactions of 3.2889(5) A between the [Ag(CN)(2)](-) in the 2-D array and the remaining free [Ag(CN)(2)](-). [Ni(en)][Ni(CN)(4)].2.5H(2)O (4) was identified as a byproduct in the reaction to prepare the previously reported [Ni(en)(2)Ag(2)(CN)(3)][Ag(CN)(2)] (3). In [Ni(tren)Ag(CN)(2)][Ag(CN)(2)] (5, tren = tris(2-aminoethyl)amine), [Ni(tren)](2+) cations are linked in a cis fashion by [Ag(CN)(2)](-) anions to form a 1-D chain similar to the [Au(CN)(2)](-) analogue. [Cu(en)Cu(CN)(2)Ag(CN)(2)] (6) is a trimetallic polymer consisting of interpenetrating (6,3) nets stabilized by d(10)-d(10) interactions between Cu(I)-Ag(I) (3.1000(4) A). Weak antiferromagnetic coupling has been observed in 2, and a slightly stronger exchange has been observed in 6. The Ni(II) complexes, 4 and 5, display weak antiferromagnetic interactions as indicated by their relatively larger D values compared to that of 3. Magnetic measurements on isostructural [Ni(tren)M(CN)(2)][M(CN)(2)] (M = Ag, Au) show that Ag(I) is a more efficient mediator of magnetic exchange as compared to Au(I). The formation of [Ni(CN)(4)](2)(-), [Ag(2)(CN)(3)](-), and [Cu(CN)(2)](-) are all attributed to secondary reactions of the dissociation products of the labile KAg(CN)(2).     

Between Ni(mnt)2 and Ni(tfd)2 dithiolene complexes: the unsymmetrical 2-(trifluoromethyl)acrylonitrile-1,2-dithiolate and its nickel complexes

A novel 1,2-dithiolate ligand, that is, the 2-(trifluoromethyl)acrylonitrile-1,2-dithiolate, abbreviated here as tfadt, is prepared from the corresponding cyclic dithiocarbonate. This ligand, substituted with both a CN and a CF(3) group, is compared with the well-known maleonitrile- and bis(trifluoromethyl)ethane-1,2-dithiolates. The preparation, electrochemical properties, and X-ray crystal structures of the square-planar nickel complexes, in both their dianionic diamagnetic [Ni(tfadt)(2)](2)(-) and their monoanionic paramagnetic [Ni(tfadt)(2)](*)(-) forms, are reported, as n-Bu(4)N(+), PPh(4)(+), and (18-crown-6)Na(+) salts, respectively. In the [(18-crown-6)Na](2)[Ni(tfadt)(2)] salt, each CN moiety of the [Ni(tfadt)(2)](2)(-) dianion is coordinated to a (18-crown-6)Na(+) cation through a CN...Na interaction [N...Na = 2.481(3) A], affording an "axle with wheels" model where two MeOH molecules act as axle caps. On the other hand, in [(18-crown-6)Na][Ni(tfadt)(2)], each (18-crown-6)Na(+) cation is coordinated on both sides by the CN groups of two monoanionic [Ni(tfadt)(2)](*)(-) complexes with N...Na(+) distances at 2.434(5) and 2.485(4) A, giving rise to heterobimetallic chains with alternating (18-crown-6)Na(+) and [Ni(tfadt)(2)](*)(-) ions. These two examples demonstrate the attractive ability of the CN moieties in the [Ni(tfadt)(2)](2)(-)(,)(*)(-) complexes to coordinate metallic cationic centers. The paramagnetic salts of the anionic [Ni(tfadt)(2)](*)(-) complex follow Curie-type law in the 2-300 K temperature range, indicating the absence of intermolecular magnetic interactions in the solid state. The complexes are found in their trans form in all crystal structures, while density functional theory calculations establish that both forms have essentially the same energy. A cis-trans interconversion process is observed by variable-temperature NMR on the dianionic [Ni(tfadt)(2)](2)(-) complex with a coalescence temperature T(c) of 260 K and a free energy of activation of 51-53 kJ mol(-)(1).     

Redox-switched complexation/decomplexation of K(+) and Cs(+) by molecular cyanometalate boxes

The reaction of [N(PPh(3))(2)][CpCo(CN)(3)] and [Cb*Co(NCMe)(3)]PF(6) (Cb* = C(4)Me(4)) in the presence of K(+) afforded {K subset[CpCo(CN)(3)](4)[Cb*Co](4)}PF(6), [KCo(8)]PF(6). IR, NMR, ESI-MS indicate that [KCo(8)]PF(6) is a high-symmetry molecular box containing a potassium ion at its interior. The analogous heterometallic cage {K subset[Cp*Rh(CN)(3)](4)[Cb*Co](4)}PF(6) ([KRh(4)Co(4)]PF(6)) was prepared similarly via the condensation of K[Cp*Rh(CN)(3)] and [Cb*Co(NCMe)(3)]PF(6). Crystallographic analysis confirmed the structure of [KCo(8)]PF(6). The cyanide ligands are ordered, implying that no Co-CN bonds are broken upon cage formation and ion complexation. Eight Co-CN-Co edges of the box bow inward toward the encapsulated K(+), and the remaining four mu-CN ligands bow outward. MeCN solutions of [KCo(8)](+) and [KRh(4)Co(4)](+) were found to undergo ion exchange with Cs(+) to give [CsCo(8)](+) and [CsRh(4)Co(4)](+), both in quantitative yields. Labeling experiments involving [(MeC5H4)Co(CN)(3)]- demonstrated that Cs(+)-for-K(+) ion exchange is accompanied by significant fragmentation. Ion exchange of NH(4+) with [KCo(8)](+) proceeds to completion in THF solution, but in MeCN solution, the exclusive products were [Cb*Co(NCMe)(3)]PF(6) and the poorly soluble salt NH(4)CpCo(CN)(3). The lability of the NH(4+)-containing cage was also indicated by the rapid exchange of the acidic protons in [NH(4)Co(8)](+). Oxidation of [MCo(8)](+) with 4 equiv of FcPF(6) produced paramagnetic (S = 4/2) [Co(8)](4+), releasing Cs(+) or K(+). The oxidation-induced dissociation of M(+) from the cages is chemically reversed by treatment of [Co(8)](4+) and CsOTf with 4 equiv of Cp(2)Co. Cation recognition by [Co(8)] and [Rh(4)Co(4)] cages was investigated. Electrochemical measurements indicated that E(1/2)(Cs(+))--E(1/2)(K(+)) approximately 0.08 V for [MCo(8)](+).     

Aggregation of [Au(CN)4]- anions: examination by crystallography and 15N CP-MAS NMR and the structural factors influencing intermolecular Au···N interactions

To investigate the factors influencing the formation of intermolecular Au···NC interactions between [Au(CN)(4)](-) units, a series of [cation](n+)[Au(CN)(4)](n) double salts was synthesized, structurally characterized and probed by IR and (15)N{(1)H} CP-MAS NMR spectroscopy. Thus, [(n)Bu(4)N][Au(CN)(4)], [AsPh(4)][Au(CN)(4)], [N(PPh(3))(2)][Au(CN)(4)], [Co(1,10-phenanthroline)(3)][Au(CN)(4)](2), and [Mn(2,2';6',2'-terpyridine)(2)][Au(CN)(4)](2) show [Au(CN)(4)](-) anions that are well-separated from one another; no Au-Au or Au···NC interactions are present. trans-[Co(1,2-diaminoethane)(2)Cl(2)][Au(CN)(4)] forms a supramolecular structure, where trans-[Co(en)(2)Cl(2)](+) and [Au(CN)(4)](-) ions are found in separate layers connected by Au-CN···H-N hydrogen-bonding; weak Au···NC coordinate bonds complete octahedral Au(III) centers, and support a 2-D (4,4) network motif of [Au(CN)(4)](-)-units. A similar structure-type is formed by [Co(NH(3))(6)][Au(CN)(4)](3)·(H(2)O)(4). In [Ni(1,2-diaminoethane)(3)][Au(CN)(4)](2), intermolecular Au···NC interactions facilitate formation of 1-D chains of [Au(CN)(4)](-) anions in the supramolecular structure, which are separated from one another by [Ni(en)(3)](2+) cations. In [1,4-diazabicyclo[2.2.2]octane-H][Au(CN)(4)], the monoprotonated amine cation forms a hydrogen-bond to the [Au(CN)(4)](-) unit on one side, while coordinating to the axial sites of the gold(III) center through the unprotonated amine on the other, thereby generating a 2-D (4,4) net of cations and anions; an additional, uncoordinated [Au(CN)(4)](-)-unit lies in the central space of each grid. This body of structural data indicates that cations with hydrogen-bonding groups can induce intermolecular Au···NC interactions, while the cationic charge, shape, size, and aromaticity have little effect. While the ν(CN) values are poor indicators of the presence or absence of N-cyano bridging between [Au(CN)(4)](-)-units (partly because of the very low intensity of the observed bands), (15)N{(1)H} CP-MAS NMR reveals well-defined, ordered cyanide groups in the six diamagnetic compounds with chemical shifts between 250 and 275 ppm; the resonances between 260 and 275 ppm can be assigned to C-bound terminal ligands, while those subject to CN···H-N bonding resonate lower, around 250-257 ppm. The (15)N chemical shift also correlates with the intermolecular Au···N distances: the shortest Au-N distances also shift the (15)N peak to lower frequency. This provides a real, spectroscopically measurable electronic effect associated with the crystallographic observation of intermolecular Au···NC interactions, thereby lending support for their viability.     

Color tuning of a nickel complex with a novel N2S2 pyridine-containing macrocyclic ligand

The novel pyridine-containing 14-membered macrocycle 3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L), which contains an N2S2 donor set, was synthesized, and its protonation behavior was studied by absorption titration with CH3SO3H. The reaction of L with Pd(II) was studied spectroscopically, and the square-planar complex [Pd(L)](BF4) was isolated and characterized. The reactions between L and NiX2 x 6 H2O (X = BF4, ClO4) in ethanol or acetonitrile afforded the octahedral complexes [Ni(CH3CN)(H2O)(L)](X)2 and [Ni(H2O)2(L)](X)2, respectively. The square-planar complexes [Ni(L)](X)2 were obtained by heating these octahedral complexes. Spectrophotometric titrations of [Ni(L)](BF4)2 were performed with neutral and negatively charged ligands. The color of nitromethane solutions of this square-planar complex turns from red to cyan, purple, blue, yellow-green, and pink following addition of halides, acetonitrile, water, pyridine, and 2,2'-bipyridine, respectively. X-ray structural analyses were carried out on the {[Ni(ClO4)(H2O)(L)][Ni(H2O)2(L)]}(ClO4)3, [Ni(CH3CN)(H2O)(L)](ClO4)2, [{Ni(L)}2(mu-Cl)2](ClO4)2, and [{Ni(L)}2(mu-Br)2]Br2 x 2 CH3NO2 complexes.     

Magnetic properties of isostructural M(H2O)4[Au(CN)4]2-based coordination polymers (M = Mn, Co, Ni, Cu, Zn) by SQUID and μSR studies

A series of isomorphous M(H(2)O)(4)[Au(CN)(4)](2)·4H(2)O (M = Mn, Co, Ni, Zn; Cu is similar) coordination polymers was synthesized from the reaction of M(II) with KAu(CN)(4); they consist of octahedrally coordinated metal centres with four equatorial water molecules and trans-axial N-cyano ligands from [Au(CN)(4)](-) moieties, generating a linear 1-D chain of M(H(2)O)(4)[Au(CN)(4)]-units. An additional interstitial [Au(CN)(4)](-) unit forms AuN and hydrogen bonds with adjacent chains. The Cu(II) system readily loses water to yield Cu[Au(CN)(4)](2)(H(2)O)(4), which was not structurally characterized. The magnetic properties of these polymers were investigated by a combination of SQUID magnetometry and zero-field muon spin relaxation (ZF-μSR). Only weak antiferromagnetic interactions along the chains are mediated by the [Au(CN)(4)]-units, but the ZF-μSR data indicates that interchain interactions yield a phase transition to a magnetically ordered state for Cu[Au(CN)(4)](2)(H(2)O)(4) below 0.6 K, while for M(H(2)O)(4)[Au(CN)(4)](2)·4H(2)O (M = Co), depopulation of zero-field split Kramer's doublets to an effective "S = 1/2" ground state yields a transition to a spin-frozen magnetic state below 0.26 K. On the other hand, only a simple slowing-down of spins above 0.02 K is observed for the more weakly zero-field split M(H(2)O)(4)[Au(CN)(4)](2)·4H(2)O (M = Mn, Ni) complexes.     

Redox properties of the ferricyanide ion on electrodes coated with layer-by-layer thin films composed of polysaccharide and poly(allylamine)

Polyelectrolyte multilayer thin films were prepared by an alternate deposition of poly(allylamine hydrochloride) (PAH) and anionic polysaccharides {carboxymethylcellulose (CMC) and alginic acid (AGA)} on the surface of a gold (Au) disk electrode, and the binding of ferricyanide [Fe(CN)(6)](3)(-) and hexaammine ruthenium ions [Ru(NH(3))(6)](3+) to the films was evaluated. Poly(acrylic acid) (PAA) was also employed as a reference polyanion bearing carboxylate side chains. A quartz-crystal microbalance study showed that PAH-CMC and PAH-AGA multilayer films grow exponentially as the number of depositions increases. The thicknesses of five bilayers of (PAH-CMC)(5) and (PAH-AGA)(5) films were estimated to be 150 +/- 20 and 90 +/- 15 nm, respectively, in the dry state. The PAH/polysaccharide multilayer film-coated Au electrodes exhibited a redox response to the [Fe(CN)(6)](3)(-) ion dissolved in solution, irrespective of the sign of the surface charge of the film, suggesting the high permeability of the films to the [Fe(CN)(6)](3)(-) ion. In contrast, the PAH-PAA film-coated Au electrodes exhibited a redox response only when the outermost surface of the film was covered with a positively charged PAH layer. However, the permeation of the [Ru(NH(3))(6)](3+) cation was severely suppressed for all of the multilayer films. It was possible to confine the [Fe(CN)(6)](3)(-) ion in the films by immersing the film-coated electrodes in a 1 mM [Fe(CN)(6)](3)(-) solution for 15 min. Thus, the [Fe(CN)(6)](3)(-)-confined electrodes exhibited a cyclic voltammetric response in the [Fe(CN)(6)](3)(-) ion-free buffer solution. The loading of the [Fe(CN)(6)](3)(-) ion in the films was higher when the surface charge of the film was positive and increased with increasing film thickness. It was also found that the [Fe(CN)(6)](3)(-) ion confined in the films serves as an electrocatalyst that oxidizes ascorbic acid in solution.     

Heterometallic MIIRuIII2 compounds constructed from trans-[Ru(Salen)(CN)2]- and trans-[Ru(Acac)2(CN)2]-. Synthesis, structures, magnetic properties, and density functional theoretical study

The synthesis, structures, and magnetic properties of four cyano-bridged M(II)Ru(III)2 compounds prepared from the paramagnetic Ru(III) building blocks, trans-[Ru(salen)(CN)2]- 1 [H2salen = N,N'-ethylenebis(salicylideneimine)] and trans-[Ru(acac)2(CN)2]- (Hacac = acetylacetone), are described. Compound 2, {Mn(CH3OH)4[Ru(salen)(CN)2]2}.6CH3OH.2H2O, is a trinuclear complex that exhibits antiferromagnetic coupling between Mn(II) and Ru(III) centers. Compound 3, {Mn(H2O)2[Ru(salen)(CN)2]2.H2O}n, has a 2-D sheetlike structure that exhibits antiferromagnetic coupling between Mn and Ru, leading to ferrimagnetic-like behavior. Compound 4, {Ni(cyclam)[Ru(acac)2(CN)2]2}.2CH3OH.2H2O (cyclam = 1,4,8,11-tetraazacyclotetradecane), is a trinuclear complex that exhibits ferromagnetic coupling. Compound 5, {Co[Ru(acac)2(CN)2]2}n, has a 3-D diamond-like interpenetrating network that exhibits ferromagnetic ordering below 4.6 K. The density functional theory (DFT) method was used to calculate the molecular magnetic orbitals and the magnetic exchange interaction between Ru(III) and M(II) (Mn(II), Ni(II)) ions.     

Structural organization and dimensionality at the hands of weak intermolecular Au···Au, Au···X and X···X (X = Cl, Br, I) interactions

The salts K[AuCl(2)(CN)(2)]·H(2)O (1), K[AuBr(2)(CN)(2)]·2H(2)O (2) and K[AuI(2)(CN)(2)]·?H(2)O (3) were synthesized and structurally characterized. Compound 1 crystallizes as a network of square planar [AuCl(2)(CN)(2)](-) anions separated by K(+) cations. However, 2 and 3 feature 2-D sheets built by the aggregation of [AuX(2)(CN)(2)](-) anions via weak, intermolecular X···X interactions. The mixed anion double salts K(3)[Au(CN)(2)](2)[AuBr(2)(CN)(2)]·H(2)O (4) and K(5)[Au(CN)(2)](4)[AuI(2)(CN)(2)]·2H(2)O (5) were also synthesized by cocrystallization of K[Au(CN)(2)] and the respective K[AuX(2)(CN)(2)] salts. Similarly to 2 and 3, the [Au(CN)(2)](-) and [AuX(2)(CN)(2)](-) anions form 2-D sheets via weak, intermolecular Au(I)···X and Au(I)···Au(I) interactions. In the case of 5, a rare unsupported Au(I)···Au(III) interaction of 3.5796(5) ? is also seen between the two anionic units. Despite the presence of Au(I) aurophilic interactions of 3.24-3.45 ?, neither 4 nor 5 exhibit any detectable emission at room temperature, suggesting that the presence of Au(I)···X or Au(I)···Au(III) interactions may affect the emissive properties.     

Structures and magnetism of {Ni2Na2}, {Ni4} and {Ni6(II)Ni(III)} 2-hydroxy-3-alkoxy-benzaldehyde clusters

Three polynuclear complexes, [NiNa(μ(1,1,1)-N(3))(μ-hmb)(2)(DMF)](2), (1), [Ni(4)(μ(3)-OMe)(4)(heb)(4)(MeOH)(1.05)(H(2)O)(2.95)], (2) and [Ni(III)(OH)(6)(hmb)(6)Ni(II)(6)]·(ClO(4))(3) (3) (Hhmb = 2-hydroxy-3-methoxy-benzaldehyde; Hheb = 2-hydroxy-3-ethoxy-benzaldehyde), were prepared by reaction of the appropriate ligand with nickel(II) perchloride hexahydrate under solvothermal conditions. All compounds were characterized by elemental analysis, IR spectroscopy and X-ray single-crystal diffraction. Compound 1 exhibits a centrosymmetric heterotetranuclear cluster which represents the first nickel complex to possess two connected face-sharing cubes structure {Ni(2)Na(2)N(2)O(4)}. Compound 2 has a tetranuclear Ni cluster with a cubane topology in which the Ni(II) and the oxygen atoms from the methanol ligands occupying alternate vertices of the cube. Compound 3 consisits of a mixed-valence [Ni(III)(OH)(6)(hmb)(6)Ni(II)(6)](3+) subunits and it represents the first nickel {Ni(II)(6)Ni(III)} complex to possess a planar hexagonal disc-like structure. The results show that the minor ligand modifications or solvent change have a key role in the structural control of the self-assembly process. Magnetic properties of 1-3 in the 300-2 K have been discussed. The {Ni(2)Na(2)} (1) and {Ni(4)} (2) core display dominant ferromagnetic interactions from the nature of the binding modes through μ(3)-N(3)(-) or μ(3)-OCH(3)(-), while {Ni(II)(6)Ni(III)} core (3) displays dominant anti-ferromagnetic interactions from the nature of the binding modes through μ(3)-OH(-).     

A versatile solvent-free mechanochemical route to the synthesis of heterometallic dicyanoaurate-based coordination polymers

The solid-state mechanochemical method was proved to be a fast, simple, and efficient route to the synthesis of heterometallic [Au(CN)(2)]-based coordination polymers. Thus, a series of mixed-metal complexes, such as KCo[Au(CN)(2)](3), KNi[Au(CN)(2)](3), Cu(H(2)O)(2)[Au(CN)(2)](2), and Zn[Au(CN)(2)](2), was obtained by grinding stoichiometric amounts of K[Au(CN)(2)] and transition metal(II) chlorides. This solid-state method rapidly yields pure dicyanoaurate-based compounds, also in cases when the aqueous solution synthesis leads to an unseparable mixture of products. In addition, in some cases, the solid state reaction was faster than the corresponding solvent-based reaction. This mechanochemical method can be applied also to main group metals to obtain various cyanoaurate-based heterometallic coordination polymers, such as Me(2)Sn[Au(CN)(2)](2) and Ph(3)Sn[Au(CN)(2)]. For the 2:1 mixture of K[Au(CN)(2)] and Me(2)SnCl(2), the dramatic enhancement of the reaction rate by the presence of a minor amount of water was noticed. In Ph(3)Sn[Au(CN)(2)], as was revealed by single-crystal X-ray diffraction, each Ph(3)Sn unit is linked to two others by two Au(CN)(2) bridges via Sn-N bonds to form an infinite cyanide-bridged chain. There are no Au···Au contacts between the chains due to the sterical hindrance of the phenyl groups. A dehydrated blue Co[Au(CN)(2)](2) complex was obtained during grinding or heating of the moderate-pink Co(H(2)O)(2)[Au(CN)(2)](2) complex. This complex displays a vapochromic response when exposed to a variety of organic solvents, as well as water and ammonia vapors.     

Discrete Rh(III)/Fe(II) and Rh(III)/Fe(II)/Co(III) cyanide-bridged mixed valence compounds

The heterotrinuclear complexes trans- and cis-[{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) are unprecedented examples of mixed valence complexes based on ferrocyanide bearing three different metal centers. These complexes have been assembled in a stepwise manner from their {trans-III-L(14S)Co(III)}, {cis-VI-L(15)Rh(III)}, and {Fe(II)(CN)(6)} building blocks. The preparative procedure follows that found for other known discrete assemblies of mixed valence dinuclear Cr(III)/Fe(II) and polynuclear Co(III)/Fe(II) complexes of the same family. A simple slow substitution process of [Fe(II)(CN)(6)](4-) on inert cis-VI-[Rh(III)L(15)(OH)](2+) leads to the preparation of the new dinuclear mixed valence complex [{cis-VI-L(15)Rh(III)(μ-NC)}Fe(II)(CN)(5)](-) with a redox reactivity that parallels that found for dinuclear complexes from the same family. The combination of this dinuclear precursor with mononuclear trans-III-[Co(III)L(14S)Cl](2+) enables a redox-assisted substitution on the transient {L(14S)Co(II)} unit to form [{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+). The structure of the final cis-[{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) complex has been established via X-ray diffraction and fully agrees with its solution spectroscopy and electrochemistry data. The new species [{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) and [{cis-VI-L(15)Rh(III)(μ-NC)}Fe(II)(CN)(5)](-) show the expected electronic spectra and electrochemical features typical of Class II mixed valence complexes. Interestingly, in the trinuclear complex, these features appear to be a simple addition of those for the Rh(III)/Fe(II) and Co(III)/Fe(II) moieties, despite the vast differences existent in the electronic spectra and electrochemical properties of the two isolated units.