The structure of a dinuclear silver(I) complex: Ag2[S2C2(CN)2] [P(C6H5)3]4

The crystal structure of the dimeric Ag maleonitriledithiolate complex, Ag₂[S₂C₂(CN)₂] [P(C₆- H₅)₃]₄ (1), has been performed. Complex 1 crystallizes in the space group P2₁/c with a = 12.2898(77), b = 23.8325(91), c = 23.1790(118) Å, β = 101.315(43)° and Z = 4. Refinement using 3253 reflections with F_o²>3σ(F_o²) yielded R = 0.0662, R_w= 0.0669. The most interesting aspect of the structure is the strong bridging interaction of the chelating maleonitriledithiolate ligand with the second Ag center, where a Ag-S distance of 2.478 Å is observed. The residual bonding capability of the sulfur atoms in the chelating anion [Ag(S₂C₂(CN)₂)(PPh₃)₂]⁻ for [Ag(PPh₃)₂]⁺ is demonstrated.     

Crystal structure of [Sm(OPMePh2)4I2]I. A cationic octahedral complex of samarium(III)

The crystal structure of [Sm(OPMePh₂)₄I₂]I, 1, was determined by X-ray diffraction and refined anisotropically to a final R value of 0.067 from 3040 reflections with I>3.0σ(I). The space group was P2/a and Z=2. The unit cell dimensions were: a= 17.777(6), b=13.559(2), c=11.656(4) Å, α=γ= 90.0 and β=97.25(3)°. The cation geometry was octahedral with the Sm(III) bonded to two mutually trans I⁻ ions and four OPMePh₂ groups. A third non-bonded I⁻ was present elsewhere in the cell. The SmI and SmO distances were 3.077(1) and 2.27(1) Å respectively. Two of the SmOP angles were 172.1(6)° and the other two were 162.0(6)°.     

The tungsten-tungsten triple bond. XV. Synthesis,structure and reactivity of 1,2-W2[CH(SiMe3)2]2(NMe2)4: the remarkable inertness of a sterically-encumbered tungsten-amido complex

Addition of 1,2-W₂Cl₂(NMe₂)₄(W≡W) to a toluene slurry of LiCH(SiMe₃)₂(2 equiv) results in the formation of 1,2-W₂[CH(SiMe₃)₂]₂(NMe₂)₄(W≡W) (I) in 79% isolated yield. Compound I has been characterized by ¹H and ¹³C NMR, IR, elemental analysis and single-crystal X-ray diffraction. The molecule exists exclusively in the gauche conformation in solution and in the solid state with WW = 2.320(1) Å. Compound I is very sterically encumbered as evidenced by: (1) large WWC angles, 110°, at the disyl ligand; (2) skewing of the NC₂ planes of the NMe₂ ligands off the WW vector; (3) anomalously large barriers to WNM₂ bond rotation in solution; (4) the inertness of I towards CO₂ and alcohols. However, compound I reacts with acetic anhydride to form 1,2-W₂[CH(SiMe₃)₂]₂(O₂CMe)₄(W≡W) (II) in 31% isolated yield. Compound II has been characterized by ¹H and ¹³C NMR, IR, and elemental analysis. The mechanistic implications of these studies with regard to alcoholysis and CO₂ insertion reactions of other 1,2-W₂R₂(NMe₂)₄ compounds are discussed. Crystal data for 1,2-W₂[CH(SiMe₃)₂]₂(NMe₂)₄ at −140°C: space group P2₁/n, a = 12.555(3), b = 18.699(5), c = 15.214(4) Å, β = 95.24(1)° and Z = 4.     

The synthesis and molecular structure of diiodooctacarbonyldiosmium(I), [Os2(CO)8I2]

The compound, diiodooctacarbonyldiosmium(I), [Os₂(CO)₈I₂], has been prepared by a route involving only atmospheric pressures. Its structure has been determined by X-ray crystallography. The crystals are tetragonal with a = 11.791(2), c = 23.583(4) Å, Z = 8, D_c = 3.48 Mg m⁻³. A total of 1637 reflections were collected out to θ = 25° on a CAD4 diffractometer in ω—2θ mode using Mo Kα (λ = 0.7107 Å) radiation. Lp and empirical absorption corrections were applied. The structure was solved in the space group I4₁cd using conventional heavy atom methods and refined to R = 0.0477 [R_w = 0.0424, w = (σ²F)⁻¹]. The molecule of [Os₂(CO)₈l₂] has two crystallographically equivalent halves joined by a single OsOs bond of length 2.947(3) )Å. There are no bridging ligands. The geometry about each osmium is pseudo-octahedral and the iodine atoms occupy equatorial positions with an OsI distance of 2.767(3) Å. The equatorial ligands on one osmium atom are staggered with respect to the equatorial ligands on the other osmium atom.     

Optical activity of dimolybdenum complex induced by chiral,chelating diamine ligand; syntheses and structures of [Mo2(O2CCF3)2(S,S-dach)2(CH3CN)2][BF4]2 and [Mo2(O2CCF3)2(R,R-dach)2(CH3CN)2][BF4]2 (dach=1,2-diaminocyclohexane)

The first structurally characterized, quadruply bonded complexes containing chiral diamine ligands, [Mo₂(O₂CCF₃)₂(S,S-dach)₂(CH₃CN)₂][BF₄]₂ (1), and [Mo₂(O₂CCF₃)₂(R,R-dach)₂(CH₃CN)₂][BF₄]₂ (2); (dach=1,2-diaminocyclohexane) were prepared by reactions of [Mo₂(O₂CCF₃)₂(CH₃CN)₆][BF₄]₂ with S,S-dach and R,R-dach, respectively, in CH₃CN. Their UV–Vis and circular dichroism (CD) spectra have been recorded and their structures determined by X-ray crystallography. Crystals of complexes 1 and 2 conform to the space groups P2 with two independent half molecules in the asymmetric unit. The two molecules have a similar structure consisting of a Mo₂ unit bridged by two cis-trifluoroacetate ligands and chelated by two dach ligands. Two acetonitrile molecules are coordinated to the Mo centers along the MoMo bond. The absorption wavelength at 507 nm for both 1 and 2 can be assigned to δ_xy→δ_xy* transitions. The solution CD spectra of these two complexes show two prominent bands at 525 and 385 nm and form mirror images of each other. The solid CD spectra of complexes 1 and 2 show marked red-shift in the absorption energies as compared with those measured in solution. The one-electron static coupling mechanism was invoked to explain the CD spectra for these complexes and the second lowest energy bands were assigned to be δ_xy→δ_x²−y² transitions.     

Synthesis, magnetic properties and crystal structures of two compounds: [Cu(en)(H2O)]2[Fe(CN)6]·4H2O and [Cu(en)2][KFe(CN)6] (en=ethylenediamine)

Two new heterometallic complexes, [Cu(en)(H₂O)]₂[Fe(CN)₆]·4H₂O (1) and [Cu(en)₂][KFe(CN)₆] (2), have been isolated from the reactions of CuCl₂ and en with K₃[Fe(CN)₆] in different molar ratios. Both complexes have been characterized by X-ray analyses, IR spectra and elemental analyses. Complex 1 is a cyanide bridged bimetallic assembly, its crystal structure consists of a two-dimensional polymeric sheet with two different rings, one a four-membered square ring and another a 12-membered hexagonal ring. The Fe(II) ion of 1 has two terminal, two linear bridging and two 1,1 en-on bridging cyanide groups. In the crystal structure of 2, the neighboring [Fe(CN)₆]³⁻ units are bridged by the K⁺ and the [K[Fe(CN)₆]]²⁻ units forming a three-dimensional network structure. The [Cu(en)₂]²⁺ units fill in the holes of the network acting as counter cations and charge compensations. Variable temperature magnetic susceptibility studies of 1 indicate that the complex exhibits ferromagnetic interaction between the Cu(II) ions.     

Synthesis and spectroscopic properties of CpRuCl(R-DAB(4e)) and CpRuCo(CO)3(R-DAB(6e)). Part XVII. X-ray structure determination of CpRuCo(CO)3(t-Bu-DAB(6e))

CpRuCl(PPh₃)₂ reacted with excess R-DAB in refluxing toluene to give CpRuCl(R-DAB(4e)) (1a: R = i-Pr; 1b: R = t-Bu; 1c: R = neo-Pent; 1d: R =p-Tol). ¹H NMR and ¹³C NMR spectroscopic data indicated that in these complexes the R-DAB ligand is bonded in a chelating 4e coordination mode.Reaction of 1a and 1b with one equivalent of [Co(CO)₄]⁻ afforded CpRuCo(CO)₃(R-DAB(6e)) (2a: R = i-Pr; 2b: R = t-Bu). The structure of 2b was determined by a single crystal X-ray structure determination. Crystals of 2b are monoclinic, space group P2₁/n, with four molecules in a unit cell of dimensions: a = 16.812(4), b = 12.233(3), c = 9.938(3) Å and β = 105.47(3)°. The structure was solved via the heavy atom method and refined to R = 0.060 and R_w = 0.065 for the 3706 observed reflections. The molecule contains a RuCo bond of 2.660(3) Å and a cyclopentadienyl group that is η⁵-coordinated to ruthenium [RuC(cyclopentadienyl) = 2.208(3) Å (mean)]. Two carbonyls are terminally coordinated to cobalt (CoC(1) = 1.746(7) and CoC(2) = 1.715(6) Å) while the third is slightly asymmetrically bridging the RuCo bond (RuC(3) = 2.025(6) and CoC(3) = 1.912(6) Å). The RuC(3)O(3) and CoC(3)O(3) angles are 138.4(5)° and 136.5(5)°, respectively. The t-Bu-DAB ligand is in the bridging 6e coordination mode: σ-N coordinated to Ru (RuN(2) = 2.125(4) Å), μ₂-N′ bridging the RuCo bond and η²-CN coordinated to Co (RuN(1) = 2.113(5), CoN(1) = 1.941(4) and CoC(4) = 2.084(5) Å). The η²-CN′ bonded imine group has a bond length of 1.394(7) Å indicating substantial π-backbonding from Co into the anti-bonding orbital of this CN bond.¹H NMR spectroscopy indicated that 2a and 2b are fluxional on the NMR time scale. The fluxionality of 6e bonded R-DAB ligands is rarely observed and may be explained by the reversible interchange of the σ-N and η²-CN′ coordinated imine parts of the R-DAB ligand.     

Preparation,properties and crystal structures of nickel(II) complexes with acyclic schiff bases derived from 2,6-diformyl-4-chlorophenol and 1,5-diamino-3-thiapentane or 3,3′-diamino-N-methyl-dipropylamine

Nickel(II) complexes with the compartmental Schiff bases derived from 2,6-diformyl-4-chlorophenol and 1,5-diamino-3-thiapentane (H₂L¹) or 3,3′-diamino-N-methyl-dipropylamine (H₂L²) were synthesized, and the crystal structures of [Ni(L¹)- (py)₂] and [Ni(L²)(dmf)]·H₂0 were determined by X-ray crystallography.Ni(L¹)(py)₂ is monoclinic, space group C2/c, with a= 18.457(6), b = 11.116(7), c= 16.098(6) Å, and β = 115.79(5)°; D_c = 1.49 g cm⁻³ for Z = 4. The structure was refined to the final R of 6.9%. The molecule has C₂ symmetry. The nickel atom is six-coordinated octahedral. Selected bond lengths are: NiO 2.04(1) Å, NiN (L¹) 2.08(1) Å, NiN(py) 2.17(1) Å.[Ni(L²)(dmf)]·H₂O is monoclinic, space group P2₁/n, with a = 17.329(6), b = 13.322(7), c = 12.476(7) Å and β = 95.43(5)°; D_c = 1.45 g cm⁻³ for Z = 4. The structure was refined to the final R of 5.1%. The nickel atom is bonded in the octahedral geometry to the bianionic pentadentate ligand L² and to one molecule of dimethylformamide. Selected bond lengths are: NiO (charged) 2.063(3) Å (mean value), NiO (neutral) 2.120(3) Å, NiN (planar) 2.050(3) Å (mean value), NiN (tetrahedral) 2.177(3) Å.     

The kinetics of ligand substitution in bis(N-alkylsalicylaldiminato)nickel(II) Complexes: a study on the reactivity of square-planar versus octahedral coordination

The bis(N-alkylsalicylaldiminato)nickel(II) complexes Ni(R-sal)₂ with R = CH(CH₂OH)CH(OH)Ph (I), R = CH(CH₃)CH(OH)Ph (II) and R = CH₂CH₂Ph (III; Ph = phenyl) were prepared and characterized. In the solid state I and II are paramagnetic (μ = 3.2 and 3.3 BM at 20 °C, respectively), whereas III is diamagnetic. It follows from the UV-Vis spectra that in acetone solution I is six-coordinate octahedral and III is four-coordinate planar, the spectrum of II showing characteristics of both modes of coordination. Vis spectrophotometry and stopped-flow spectrophotometry were applied to study the kinetics of ligand substitution in I–III by H₂salen (= N,N′-disalicylidene-ethylenediamine) in the solvent acetone at different temperatures. The kinetics follow a second-order rate law, rate = k[H₂-salen] [complex]. At 20 °C the sequence of rate constants is k(III):k(II):k(I) = 11 850:40.6:1. The activation parameters are ΔH^≠(I) = 112, ΔH^≠(II) = 40.7, ΔH^≠(III) = 35.7 kJ mol⁻¹ and ΔS^≠(I) = 92, ΔS^≠(II) = −103, ΔS^≠(III) = −89 J K⁻¹ mol⁻¹. The enormous difference in rate between complexes I, II and III, which is less pronounced in methanol, is attributed to the existence of a fast equilibrium planar ⇌ octahedral, which is established in the case of I and II by intramolecular octahedral coordination through the hydroxyl groups present in the organic group R. An A-mechanism is suggested to control the substitution in the sense that the entering ligand attacks the four-coordinate planar complex, the octahedral complex being kinetically inert.     

The crystallochemistry of tetracyanocomplexes. The crystal and molecular structures of tris(1,2-diaminoethane)zinc(II) tetracyanoniccolate(II) monohydrate and tris(1,2-diaminoethane)zinc(II) tetracyanoniccolate(II)

C₁₀H₂₆N₁₀ONiZn, tris(1,2-diaminoethane) zinc(II) tetrakis(cyano)niccolate(II) monohydrate (I), orthorhombic, Pbca, a = 1.1680(4), b = 1.5844(3), c = 1.9981(6) nm, Z = 8 d(meas) = 1.54, d(calc) = 1.53 g cm^?3. C₁₀H₂₄N₁₀NiZn, tris(1,2-diaminoethane) zinc(II) terakis(cyano)niccolate(II), (II), monoclinic, P2₁/n, a = 0.7957(2), b = 1.5170(5), c = 1.4932(4) nm, β = 96.41(2)°, Z = 4, d(meas) = 1.49, d(calc) = 1.51 g cm^?3. Both the structures (I) and (II) have been solved by the heavy atom method and refined by full-matrix least-squares to R(I) = 0.086 for 1890 independent reflections and R(II) = 0.058 for 1689 independent reflections, respectively. In the case of (II) the superlattice structure problem was solved. The crystal structure of (I) consists of [Zn(en)₃]²⁺ cations, [Ni(CN)₄]^2? anions and water molecules. Two of the cyano groups in trans positions are bonded to water molecules by hydrogen bonds, the distances CN?O being 0.289 and 0.291 nm, respectively. The crystal structure of (II) is constituted by [Zn(en)₃]²⁺ cations and [Ni(CN)₄]^2? anions.     

The phenomenon of conglomerate crystallization. XV. Spontaneous resolution in coordination compounds. XIII. The crystallization behaviour and the crystal and molecular structure of Δ(λδ)-cis-Rh(en)2(NO2)2]Cl

The title compound, I, crystallizes in the monoclinic space group P2₁ with cell constants: a = 6.599(3), b = 11.121(2), c = 8.375(1) Å and β = 106.35(2)°; V = 589.74 ų and D(calc; Z = 2) = 1.974 g cm⁻³. The compound is isomorphous and isostructural with its Co analogue. A total of 2982 data were collected over the range of 4°  20  70°; of these, 2537 (independent and with I ⩾ 3σ(I)) were used in the structural analysis. Data were corrected for absorption (μ = 16.6 cm⁻¹) and the relative transmission coefficients ranged from 1.000 to 0.9504. Refinement was carried out for both enantiomeric configurations and the crystal used was found to contain cations with Δ(λδ) absolute configuration. The final R(F) and R_w(F) residuals were, respectively 0.0220 and 0.0239 for (−−−; i.e.Δ(λδ)) and 0.0231 AND 0.0317 FOR (+++; i.e.Λ(δλ)). Thus, the former was selected as correct for our specimen.In the case of I, as well as in the Co derivative [cis-Co(en)₂(NO₂)₂]Cl (II), the conformation of one of the rings is opposite that expected for the lowest energy conformation, which in the current case should be Δ(λλ)).The RhN(NO)₂ distances are 2.020(2) and 2.010(2) Å, while the RhN(amine) distances, trans to the NO₂ ligands are 2.085(2) and 2.093(1) Å, values distinctly longer than the other two RhN distances (2.064(1) and 2.068(1) Å). The latter are the RhN distances to the terminalNH₂ ligands located trans to each other. Thus, we observe a trans effect, which is more pronounced in I than in II, and which is of comparable magnitude to that observed in the case of the trien derivative, [cis-α-Rh(trien)(NO₂)₂]Cl(III).Parallel with an increase in metalN distances in going from [cis-α-Co(trien)NO₂)₂]Cl·H₂) (IV) to (III) is an increase in the torsional angles of the outer rings (NCCN) of about 10°. Comparison of these parameters in I and II reveal that this change is not so marked for this pair since in I they are −54.9° and 52.8° while in II they are 50.2° and −48.1°; i.e. a change of only 4°. This important difference between trien and en derivatives is caused by the presence of the central five-membered ring, which for compounds III and IV remains largely unchanged, except for the metalN distances.The NO bond lengths are 1.244(3), 1.220)(2), 1.237(2) and 1.211(2) Å, which are similar to those found for the analogous Co isomer. The CN bond lengths are 1.492(3), 1.474(2), 1.486(2) and 1.475(2) Å, while the CC bonds are 1.509(3) and 1.524(3) Å. These values are also comparable with those obtained for the Co isomer and, in fact, the pattern of the bonds is nearly identical in both, including the common feature of having a longer CC bond for the en ring with the conformation opposite that expected.As was the case with the Co analogue, the Cl⁻ anion is associated with the hydrogens of the secondary nitrogen (trans to the −NO₂) ligands, the Cl…H7 distance being 2.18(3) Å and the <Cl…H7N2 = 163°.     

Mechanisms for acceleration of halide anation reactions of platinum(IV) complexes. REOA versus ligand assistance and platinum(II) catalysis Without central ion exchange

Chloride anation of trans-Pt(CN)₄ClOH₂⁻ has been studied with and without Pt(CN)₄²⁻ present at 25.0°C by use of stopped-flow and conventional spectrophotometry and a 1.00 M perchlorate medium. The rate law in the absence of Pt(CN)₄²⁻ is Rate=(p₁ + p₂ [H⁺] ) [Cl⁻]² [complex]/(1 + q [Cl₋]) with p₁=(3.0 ± 0.1) × 10⁻⁵ M⁻²s⁻¹, p₂=(3.6 ± 0.1) × 10⁻⁵ M⁻³ s⁻¹ and q=(0.62 ± 0.02) M⁻¹. It is compatible with a chloride assistance via an intermediate of the type Cl-Cl-Pt(CN)₄···OH₂²⁻, in which the reactivity of the aqua ligand is enhanced due to a partial reduction of the platinum. This mechanism of halide assistance is in principle the same as the modified reductive elimination oxidative addition (REOA) mechanism proposed by Poë, in which the intermediate is not split into free halogen, platinum(II) and water, and in which electron transfer not necessarily involves complete reduction to platinum(II). To avoid confusion with complete reductive eliminations, reactions without split of the intermediates are here termed halide-assisted reactions. The pH-dependence indicates acid catalysis via a protonated intermediate ClClPt(CN)₄···OH₃⁻.The Pt(CN)₄²⁻accelerated path has the rate law Rate=

[Cl-] [Pt(CN)₄²⁻] [complex] where k=(39.9±0.5) M⁻² s⁻¹ and K_a=(4.0±0.2)10⁻² M is the protolysis constant of trans-Pt(CN)₄ClOH²⁻.Reaction between PtCl₅OH₂⁻ and chloride is accelerated by Pt(CN)₄²⁻ and gives PtCl₆²⁻ as the reaction product. The rate law is Rate=k [Cl⁻] [Pt(CN)₄²⁻] [PtCl₅OH₂⁻] with k=(5.6 ± 0.2)10⁻³ M⁻² s⁻¹ at 35.0°C and for a 1.50 M perchlorate acid medium. The reaction takes place without central ion exchange. Alternative mechanisms with two consecutive central ion exchanges can be excluded. The role of Pt(CN)₄²⁻ in this reaction is very similar to that of the assisting halide in the halide assisted anations. [p ]Reaction between trans-Pt(CN)₄ClOH₂⁻ and PtCl₄²⁻ gives Pt(CN)₄²⁻ and PtCl₅OH₂⁻ as products and has the rate law Rate=k[PtCl₄²⁻] [trans-Pt(CN)₄ClOH₂⁻] with k=(3.32 ± 0.02) M⁻¹ s⁻¹ at 25 °C for a 1.00 M perchloric acid medium. The formation of an aqua complex as the primary reaction product and the rate independent of [Cl⁻] shows that formation of a bridged intermediate of the type Pt(II)Cl₄ClPt(IV)(CN)₄OH₂³⁻ is formed in the initial reaction step, not five-coordinated PtCl₅³⁻.     

Syntheses and crystal structures of cyano-bridged cluster-metal layered coordination polymers [Cu(dien)]3[W4Te4(CN)12] · 9H2O and [Ni(en)(NH3)]3[W4Se4(CN)12] · 7.5H2O

Two new tetrahedral tungsten cyanide cluster compounds, [Cu(dien)]₃[W₄Te₄(CN)₁₂] · 9H₂O (1) (dien=diethylenetriamine) and [Ni(en)(NH₃)]₃[W₄Se₄(CN)₁₂] · 7.5H₂O (2) (en=ethylenediamine), were synthesized by treating aqueous solutions of the saltlike cluster compound K₆[W₄Te₄(CN)₁₂] · 5H₂O/K₆[W₄Se₄(CN)₁₂] · 6H₂O with copper(II)/nickel(II) chloride in aqueous ammonia containing dien/en. The cyano-bridged layered coordination polymeric compounds were characterized by single-crystal X-ray diffraction analysis: monoclinic, space group P2₁ for 1; trigonal, space group for 2. Structures of 1 and 2 consist of infinite neutral layers of cluster components {W₄Te₄(CN)₁₂}/{W₄Se₄(CN)₁₂} connected, one another by {Cu(dien)} or {Ni(en)(NH₃)} fragments, respectively.     

Crystal structure and magnetic measurements of [Cr(en)3] [ZnCl4]Cl

The compound [Cr(en)₃][ZnCl₄]Cl has been synthesized by reaction of CrCl₃·6H₂O, Zn and [Cr(en)₃]₂(SO₄)₃ in HCl. Its molecular and crystalline structure was determined by X-ray diffraction methods, being monoclinic, P2₁/c, a=21.215(3), b=12.532(2), c=13.707(2) Å, β=95.21°, V= 3629(2) ų, D_x=1.738g cm⁻³, MW=474.9, Z= 8, F(000)=1928, λ(Mo Kα)=0.71069 Å, μ(Mo Kα)= 27.04 cm⁻¹, 288 K. No significant exchange interactions between Cr(III) cations in the crystalline lattice were found. Curie-Weiss behavior was found in the three directions tested (g₁=2.06±0.02,g₂= 2.08±0.02,g₃=2.09±0.01), T=1.2-1.4 K.     

Structural comparison of (CuICH3CN4·dibenzo-18-crown-6 (I) and (CuICH3CN)x (II) fluorescent copper(I) materials

The single crystal X-ray structures of (CuICH₃CN₄·dibenzo-18-crown-6 (I) and (CuICH₃CN) (II) have been determined at room temperature [(I) C₂₈H₃₆Cu₄I₄N₄o₆, monoclinic space group P2₁/n, a = 10.116(4), b = 18.092(8), c = 22.211(9) Å, β = 98.66(3)°, Z = 4; (II) C₂H₃CuIN, orthorhombic pBN2₁, a = 13.618(8), b =8.742(2), c = 4.298(2), Z = 4]. (I) exists as a distorted cube with copper and iodine at alternate corners, the fourth coordination site copper occupied by an acetonitrile molecule coordinated through nitrogen. The cluster contains no crystallographic symmetry element and CuCu distances average 2.770(5) Å. The dibenzo-18-crown-6 displays only second sphere type interactions with cluster. (II) displays a pleated double chain type structure with distorted rectangles of alternating Cu and I atoms sharing opposite edges in infinite array. Copper displays tetrahedral geometry by coordination to three iodine atoms and a nitrogen bound acetonitrile molecule.     

Chair-form [Ag2(1,2-bimb)2] in silver(I) complexes containing the ditopic ligand 1,2-bis(1-imidazolylmethyl)benzene (1,2-bimb)

The ditopic ligand 1,2-bis(1-imidazolylmethyl)benzene (1,2-bimb) and its silver(I) complexes [Ag₂(1,2-bimb)₂](PF₆)₂ (1) and {[Ag₂(1,2-bimb)₂]₂(SbF₆)₄}_n (2) were prepared and their structures characterized by X-ray crystallography. Both complexes contain the chair-form unit [Ag₂(1,2-bimb)₂]²⁺ with Ag(I) linearly coordinated by N_Im (Im=1-imidazolyl) from the Im groups of two 1,2-bimb. However, the [Ag₂(1,2-bimb)₂]²⁺ units are positioned differently in forming 1D infinite chains through weak argentophilic interactions: linear chains in 1 with the units oriented in same direction are formed via Ag?π interactions, while polymeric chains constructed via Ag?Ag interactions in 2 are observed with the units arranged in alternate directions. Differences in supramolecular structures may be a result of different size of the anions.     

Syntheses,structures and ligand dissociation kinetics of Vitamin B12 model compounds with exceptionally poor electron donating groups,LCo(DH)2CHX2 (X = Cl or Br)

The syntheses and ligand dissociation kinetics of vitamin B₁₂ model compounds LCo(DH)₂CHX₂ with X = Cl and Br and L = different neutral N- and P- ligands are reported together with the crystal structures of the CHCl₂ derivatives with L = py (1) and 1,5,6-trimethylbenzimidazole, Me₃Bzm (2). Compound 1 crystallizes in the space group P2₁/n with cell parameters a = 9.617(1), b = 12.601(2), c = 15.586(2) Å, β = 95.44(1)°; 2 crystallizes in the space group P1 with cell parameters a = 8.867(2), b = 10.719(2), c = 13.345(2) Å, α = 94.81(2), β = 90.89(1), γ = 105.63(2)°. The two structures were solved by Patterson and Fourier methods and refined by least-squares methods to final R values of 0.037 (1) and 0.036 (2), using 3474 (1) and 4435 (2) independent reflections.The axial NCoC fragment is characterized by CoN and CoC distances of 2.045(2) and 1.995(2) Å in 1 and 2.043(2) and 1.983(2) Å in 2, respectively. The CoC bond lengths have the smallest values so far reported in both py and Me₃Bzm alkylcobaloximes.The displacement of the L ligand followed SN1 LIM behaviour and the corresponding rate constants depend upon the nature of L and vary in CHCl₂ derivatives from 2.42 X 10⁻¹ s⁻¹ for 2-aminopyridine to 1.99 X 10⁻⁵ s⁻¹ for P(OMe)₃. For fewer CHBr₂ analogs the rate constants were smaller.Kinetic results confirm previous findings that the donating ability of CHBr₂ is less than that of CHCl₂, although the electronegativity of Cl and Br species would suggest an opposite trend. Some relationships between kinetic and structural properties are discussed.     

Trinuclear Cu(pn)2Ag2(CN)4: preparation, crystal structure and properties (pn=1,2-diaminopropane)

The new compound Cu(pn)₂Ag₂(CN)₄ (CPAC; pn=1,2-diaminopropane) was isolated from a reaction mixture containing CuSO₄, pn and K[Ag(CN)₂] and was characterized by chemical analysis, IR and UV-VIS spectroscopy, and magnetic studies. The crystal structure of CPAC is built up of trinuclear NC-Ag-CN-Cu(pn)₂-NC-Ag-CN molecules which are linked by hydrogen bonds and argentophilic interactions (Ag?Ag=3.26141(16) Å). The Cu(II) atom is coordinated in the equatorial plane by two chelate bonded pn ligands (mean Cu-N is 2.010(1) Å, while the axial positions are occupied by linear cyanoargentate anions acting as terminal ligands (Cu-N is 2.570(2) Å (2x)). The magnetic properties are well described by the Curie law down to 2 K.