Small Bite Angle Research Articles

Bis(tetraethylammonium) bis(2-thioxo-1,3-dithiole-4,5-dithiolato)cadmium(II)

The title complex, (C8H20N)2[Cd(C3S5)2], has the Cd atom in a distorted tetrahedral geometry, due to the relatively small bite angles, 88.61 (4)–88.78 (4)°, of the 2-thio­xo-1,3-di­thiole-4,5-di­thiol­ate ligands.

Synthesis, crystal structures and magnetic properties of Cu(II) compounds bridged by the terephthalate ligand and hydrogen bonds

A 3D network [Cu(tmen)(tp)(H 2O) 2] n ( 1) (tmen = N, N, N′, N′-tetramethylethylenediamine; tp = terephthalate) and a 2D sheet [Cu(pyrazole) 2(tp)] n ( 2), featuring 1D chains interwoven by hydrogen bonds, have been prepared and characterized by means of X-ray analyses and magnetic measurements. For 1, coordinative zigzag chains contain Cu(II) centers capped by the chelate ligand tmen, in which the tetragonal structure is elongated due to Jahn–Teller distortion. Coordinated water molecules are hydrogen-bonded to two free carboxylate oxygens of tp bridges, leading to the observed 3D structure. The use of the non-chelating capping ligand pyrazole produced the covalent-bonded 1D linear compound 2 with hydrogen bonds. A severe octahedral distortion of the Cu(II) center arises from a small bite angle (52.3(1)°) of two carboxylate oxygen atoms of tp, which are in turn hydrogen-bonded to the N–H groups of pyrazole ligands coordinated to Cu(II) atoms in neighboring chains. Magnetic data were fitted with the high-temperature series expansion for the Heisenberg chain spin Hamiltonian H = − J∑ i S i · S i + 1 together with consideration of the molecular field approximation ( zJ′). Both compounds interestingly exhibit ferromagnetic interactions with g = 2.17, J = 4.08 cm −1, zJ′ = −0.28 cm −1 for 1 and g = 2.09, J = 1.47 cm −1, zJ′ = −0.04 cm −1 for 2. By taking into account structural parameters of distances between Cu atoms, it is reasonably assigned that the ferromagnetic couplings ( J > 0) in these systems originate from the hydrogen bonds. The spin density of the d x 2 - y 2 orbital on a Cu(II) atom in a chain is propagated and induced over the d z 2 orbital of another Cu(II) atom in an adjacent chain. This orbital orthogonality gives rise to such interactions. The negative zJ′ term suggests that the tp bridges communicate only tiny antiferromagnetic interactions.

Coordination Chemistry and Asymmetric Catalysis with a Chiral Diphosphonite

AbstractThe improved synthesis of the chiral diphosphonite, XantBino (1), based on a xanthene backbone and bearing chiral binaphthyl groups on both P‐atoms is described together with its PdII and RhI complexes. The 31P NMR spectra of both complexes point out that the two phosphorus atoms are chemically inequivalent. The complex cis‐[PdCl2(1)] (2) is structurally characterized by NMR spectroscopy and X‐ray crystallography. The molecular structure reveals an unusually small bite angle for this member of the xantphos family of only 100°. The rhodium‐catalyzed asymmetric hydroformylation of styrene and vinyl acetate as well as the asymmetric hydrogenation of methyl (Z)‐2‐acetamidocinnamate, applying this chiral diphosphonite 1, are described. Low enantiomeric excesses are obtained in the asymmetric hydroformylation, while use of the catalyst precursor [Rh(cod)(1)]BF4 (3) results in a promising enantiomeric excess in the Rh‐catalyzed asymmetric hydrogenation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Tetra-n-butylamine(carbonato-κ2O,O′)cobalt(III)n-butylcarbamate dihydrate

The title compound, [Co(CO3)(C4H11N)4](C5H10NO2)·2H2O, is a coordination complex with an N4O2 coordination sphere around the central CoIII ion. The small bite angle of the chelating carbonate causes a distortion of the octahedral geometry to an approximately C2v local symmetry. Hydro­gen-bonding between the carbonate, carbamate and amine groups, and the water of crystallization, results in a complex two-dimensional network.

The substitution chemistry of a useful new synthon with neutral donor ligands. Part 2. The reactions of [TcCl 3(NNPh 2)(PPh 3) 2] with neutral nitrogen and carbon ligands. The X-ray structure of [TcCl 2(NNPh 2)(bipy)(PPh 3)][PF 6], [TcCl 2(NNPh 2)(terpy)][BF 4] and [TcCl(NNPh 2)(CNCH 2Ph) 2(PPh 3) 2][PF 6

The reaction of [TcCl 3(NNPh 2)(PPh 3) 2] complex with 2,2′ bipyridine in MeOH yields [TcCl(OMe)(NNPh 2)(PPh 3)(bipy)] + which is isolated as the (BPh 4) − salt. The X-ray structure shows the diphenylisodiazene ligand and methoxide in the axial sites, with the bipyridyl ligand, triphenylphosphine and chloride in the equatorial plane. The methoxide ligand is introduced from the reaction solvent. The TcN(1) bond length is 1.755(3) Å, while N(1)N(2) is 1.298(4) Å and the TcN(1)N(2) bond angle is 171.4(2)°, which reflects the multiple bonding through out the zwitterionic isodiazene moiety. The distorted octahedral geometry results from the small bite angle associated with the bipyridine ligand which is 75.98(10)°. In the reaction of [TcCl 3(NNPh 2)(PPh 3) 2] with terpyridine in MeOH, [TcCl 2(NNPh 2)(terpy)] + is isolated as the (BF 4) − salt. The X-ray structure shows the isodiazene ligand and terpyridine ligands in the equatorial plane and the chloride ligands in a mutually trans orientation. The TcN(1) bond length is 1.739(3) Å and the N(1)N(2) bond length is 1.301(4) Å again reflecting the multiple bonding throughout the metal–nitrogen–nitrogen framework. The TcN(1)N(2) bond angle is 174.3(3)° which, along with the N(1)N(2)C bond angles of 120.3(3)° and 115.8(3)°, are indicative of sp 2 hybridization on the β-nitrogen atom. The reaction of [TcCl 3(NNPh 2)(PPh 3) 2] with RNC {where R=CH 2Ph} yields [TcCl(NNPh 2)(PPh 3) 2(CNR) 2] +, which is isolated as the (PF 6) − salt. The reaction with isonitrile results in a one electron reduction of the technetium synthon, resulting in the clean isolation of the Tc(II) product. The TcN(1) bond length is 1.832(5) Å and the N(1)N(2) bond length is 1.287(6) Å, and the TcN(1)N(2) bond angle is 157.8(4)°. This new structural conformation approaches the ‘bent’ conformation of the isodiazene MNN linkage with sp 2 hybridization on both the α- and β-nitrogen atoms. There is no sign of an NH stretch in the IR and no evidence of a proton in the X-ray structure, so the addition of NH 4PF 6 as counter ion did not protonate the isodiazene ligand's α-nitrogen.

Preparation and properties of a 4Fe4S cluster complex chelated by pyridine-2-thiolato ligands, (Et 4N) 2[Fe 4S 4(S-2-(4-NO 2)C 5H 3N) 4

A 4Fe4S cluster complex with pyridine-2-thiolato ligands, (Et 4N) 2[Fe 4S 4(S-2-(4-NO 2)C 5H 3N) 4], has been synthesized by the ligand exchange reaction. X-ray structure analysis revealed that the Fe atoms in the core are chelated by the ligands in a bidentate form. The four-membered chelate ring has a very small bite angle of NFeS=64.7°. The complex crystallizes in space group Fddd, displaying a highly symmetrical molecular structure. A quasi-reversible redox wave is observed at E 1/2=−1.46 V (vs. SCE), showing a large negative shift relative to those in ordinary arenethio analogues.

Platinum and Palladium Imido and Oxo Complexes with Small Natural Bite Angle Diphosphine Ligands

Treatment of L(2)MCl(2) (M = Pt, Pd; L(2) = Ph(2)PCMe(2)PPh(2) (dppip), Ph(2)PNMePPh(2) (dppma)) with AgX (X = OTf, BF(4), NO(3)) in wet CH(2)Cl(2) yields the dinuclear dihydroxo complexes [L(2)M(mu-OH)](2)(X)(2), the mononuclear aqua complexes [L(2)M(OH(2))(2)](X)(2), the mononuclear anion complexes L(2)MX(2), or mixtures of complexes. Addition of aromatic amines to these complexes or mixtures gives the dinuclear diamido complexes [L(2)Pt(mu-NHAr)](2)(BF(4))(2), the mononuclear amine complexes [L(2)M(NH(2)Ar)(2)](X)(2), or the dinuclear amido-hydroxo complex [Pt(2)(mu-OH)(mu-NHAr)(dppip)(2)](BF(4))(2). Deprotonation of the Pd and Pt amine or diamido complexes with M'N(SiMe(3))(2) (M' = Li, Na, K) gives the diimido complexes [L(2)M(mu-NAr)](2) associated with M' salts. Structural studies of the Li derivatives indicate association through coordination of the imido nitrogen atoms to Li(+). Deprotonation of the amido-hydroxo complex gives the imido-oxo complex [Pt(2)(mu-O)(mu-NAr)(dppip)(2)].LiBF(4).LiN(SiMe(3))(2), and deprotonation of the dppip Pt hydroxo complex gives the dioxo complex [Pt(mu-O)(dppip)](2).LiN(SiMe(3))(2).2LiBF(4).

Coordination modes of cis- P, P′-diphenyl-1,4-diphospha-cyclohexane to metal ions of Groups 9 and 10

Complexes of a tertiary diphosphine with cyclic core, cis- P, P′-diphenyl-1,4-diphospha-cyclohexane (dpdpc), with metal ions of Groups 9 and 10 have been prepared and characterised. In neutral M(0) or M(II) (M=Pt, Pd) complexes the diphosphine acts as a bridge affording polynuclear products. Instead, in cationic mononuclear Pt(II) and Pd(II) species a clear preference for chelation of dpdpc is observed. Also the cation [Ni(dpdpc) 2Cl] + contains the two dpdpc moieties as chelates. The molecular and crystal structure of [Ni(dpdpc) 2Cl] 2(NiCl 4) discloses a significantly small bite angle of the chelate and interaction of near phenyl rings pertaining to opposite dpdpc moieties. Coordination of dpdpc to cobalt prompts its oxidation to the corresponding P, P′-dioxide.

Preparation, Crystal Structures, Electrochemical and Spectroscopic Properties of Bis(2,2′-bipyridine)ruthenium(II) Complexes Containing 8-(Diphenylphosphino)quinoline or 2-(Diphenylphosphino)pyridine

Abstract Mixed-ligand bis(2,2′-bipyridine)ruthenium(II) complexes containing a hybrid donor-type P–N ligand of 8-(diphenylphosphino)quinoline (Ph2Pqn) or 2-(diphenylphosphino)pyridine (Ph2Ppy), [Ru(bpy)2(Ph2Pqn or Ph2Ppy)](PF6)2 (1 or 2; bpy = 2,2′-bipyridine), have been prepared. The X-ray crystal structure analyses of 1 and 2 revealed that Ph2Pqn and Ph2Ppy act as a bidentate ligand to form a five- and four-membered chelate ring, respectively. The four-membered chelate ring formed by Ph2Ppy has a very small bite angle (P(1)–Ru–N(1): 68.4(1)°), but the RuII(bpy)2 moiety in 2 has a typically strain-free structure. On the other hand, in the Ph2Pqn complex 1, one of the bpy planes is skewed remarkably from the Ru coordination plane due to an intramolecular steric interaction with a phenyl ring of Ph2Pqn. The redox potentials and the 1MLCT transition energies of the Ph2Pqn and Ph2Ppy complexes (1 and 2) were not so different from the averaged values of those of the corresponding 1,2-bis(diphenylphosphino)benzene (dppb) and 1,10-phenanthroline (phen) complexes, [Ru(bpy)2(dppb or phen)](PF6)2 (3 or 4). These facts indicate that the electronic asymmetry inherently present in Ph2Pqn and Ph2Ppy does not affect remarkably the ground state properties of the complexes. However, unlike complexes 2–4, the Ph2Pqn complex 1 in EtOH/MeOH (4 : 1) glass at 77 K exhibited a novel dual emission, giving a biexponential emission decay. The shorter-lived (τ = 10.8 µs) emission is attributable to the bpy-based 3MLCT emission, similar to the other RuII-polypyridine complexes, while the longer-lived (τ = 62.1 µs) emission can probably be assigned as arising from the quinoline-based 3(π–π*) excited state.

New compounds with bridging dicyanamide and bis-chelating 2,2′-bipyrimidine ligands: syntheses, structural characterisation and magnetic properties of the two-dimensional materials [Fe2(dca)4(bpym)]·H2O and [Fe2(dca)4(bpym)(H2O)2

The new polymeric, two-dimensional compounds [Fe2(dca)4(bpym)]·H2O (1) and [Fe2(dca)4(bpym)(H2O)2] (2) (dca− = dicyanamide anion and bpym = 2,2′-bipyrimidine) have been synthesised and characterised by infrared spectroscopy and X-ray crystallography. Both compounds consist of two-dimensional networks of octahedrally co-ordinated iron(II) cations, bridged by bis-bidentate 2,2′-bipyrimidine and bridging dicyanamide anions. The metals are in a distorted octahedral environment due to the small bite angle of the bpym ligands [75.3(1)° in 1 and 73.7(1)° in 2]. The main difference between the two structures is the co-ordination mode of the dca ligands. In compound 1, the iron(II) cation is linked by four dca bridging ligands and by one bis-chelating bpym. In compound 2, each iron cation is linked by two trans-bridging dicyanamide ligands, one bis-chelating bpym and two unidentate ligands in a cis arrangement (one terminal dicyanamide and one water molecule). The main consequence of the different dca co-ordination modes is that each metal cation is connected to four neighbouring metals in 1 but to only three in 2. Magnetic measurements reveal a broad maximum in the χms. T plots at ca. 11 K for both compounds, which is characteristic of antiferromagnetic exchange interactions between the high-spin iron(II) centres (J = −1.6 cm−1, g = 2.20 for 1 and J = −1.8 cm−1, g = 2.15 for 2).

Synthetic, Structural, and Solution Calorimetric Studies of Pt(CH3)2(PP) Complexes

Reaction enthalpies of the complex (COD)PtMe2 (1; COD = η4-1,5-cyclooctadiene) with an extensive series of bidentate phosphines (dpype, dppf, diop, dppe, dppb, dppp, dpmcb, depe, dmpe, dcpce) have been measured by solution calorimetry. The relative stabilities of the resulting complexes PtMe2(PP) are determined by a combination of the donor and bite angle/steric properties of the bidentate phosphine ligand. In general, good σ donor ligands with small bite angles result in more thermodynamically stable complexes. Additionally, the molecular structures of 1, Pt(Me)2(pype) (2), Pt(Me)2(dppf) (3), Pt(Me)2(diop) (4), Pt(Me)2(dppe) (6), Pt(Me)2(dpmcb) (9), and Pt(Me)2(Et2dppp) (13) have been determined by single-crystal X-ray diffraction. No correlation between the thermochemical results and the structural parameters, e.g, M−P distance (as observed in other systems), is apparent in this class of complexes.

Coordination modes of 3-hydroxypicolinic acid: synthesis and crystal structures of palladium(II), platinum(II) and rhenium(V) complexes

The new palladium and platinum complexes with 3-hydroxypicolinic acid (HpicOH) [M(PPh3)2Cl(picOH)]·CHCl3, [M(bipy)(picOH)]Cl [M=Pd(II) or Pt(II)], K[PdCl(picOH)2] and [Pt(picOH)2] and the new rhenium complexes [ReOI2(PPh3)(picOH)] and [ReO(PPh3)(picOH)2]I have been prepared. The crystal structures of [M(PPh3)2Cl(picOH)]·CHCl3 [M=Pd(II) 1 or Pt(II) 2] and [ReOI2(PPh3)(picOH)] 3 were determined by X-ray diffraction. Complex 3 exhibits a distorted octahedral geometry with the picOH− ligand showing N,O-chelation with a small bite angle O–Re–N of 74.8(3)°. In complexes 1 and 2 the metal centre is surrounded by a NP2Cl donor set in a distorted square planar arrangement. Therefore, the picOH− ligand is bound through the nitrogen atom, but the distances found between the metal and the carboxylate oxygen [Pd···O(71) 2.773(5) A or Pt···O(71) 2.734(4) A] suggest a [4+1] coordination consistent with N,O-chelation for palladium and platinum centres. Infrared, Raman, 1H and 13C-{1H} NMR spectroscopic data for the complexes are consistent with the crystallographic results. In the solid state the complex units of 1 and 3 are aggregated in centrosymmetric dimers based on C–H···Cl or C–H···O hydrogen bonding interactions between the chlorine of the Pd–Cl bond (in 1) or the phenolic oxygen of the picOH− anion (in 3) and a hydrogen atom of a phenyl group of a PPh3 ligand.

On the Influence of the Bite Angle of Bidentate Phosphane Ligands on theRegioselectivity in Allylic Alkylation

The natural bite angle of bidentate phosphane ligands influences the isomer distribution (syn and anti) in (1-methylallyl)(bisphosphane)Pd OTf complexes. It was found (31P- and 1H-NMR studies) that the syn/anti ratio changes from 12 (dppp) to 1.3 (sixantphos). Molecular orbital calculations [PM3(tm) level] indicate that for ligands inducing a large bite angle, the phenyl rings of the ligand embrace the allyl moiety, thus influencing the syn/anti ratio. This bite-angle effect on the syn/anti ratio is transferred to the regioselectivity in stoichiometric allylic alkylation. Ligands inducing large bite angles direct the regioselectivity towards the formation of the branched product 2. Catalytic alkylation of (E)-2-butenyl acetate showed that for ligands with a small bite angle the regioselectivity of the catalytic and stoichiometric alkylation are in good agreement. This correspondence is worse for ligands with a larger bite angle, which is rationalised in terms of the relative rates of syn/anti isomerisation and alkylation. The ligand with the largest bite angle (sixantphos) gives the most active catalytic species.

Synthesis, crystal structure and properties of trigonal bipyramidal [M(L5)2(H2O)]·H2O complexes [M = cobalt(II) (S = 3/2) or copper(II) (S = 1/2); HL5 = N-(2-chloro-6-methylphenyl)pyridine-2-carboxamide

Using a bidentate ligand N-(2-chloro-6-methylphenyl)pyridine-2-carboxamide (HL5), in its deprotonated form, two new five-co-ordinate complexes of composition [M(L5)2(H2O)]·H2O (M = CoII 1 or CuII 2) have been prepared and characterized including X-ray crystallography. The co-ordination geometry at CoII and CuII is approximately trigonal bipyramidal (two deprotonated amide nitrogens and a water molecule in the equatorial plane and two pyridines in the axial positions), being more distorted in the case of CuII. The observed distortion is caused by (i) a small bite angle of the chelating ligand and (ii) the presence of two ortho substituents, a chloro and a methyl group, on the phenyl ring (steric effect). To the best of our knowledge, 1 represents the first structurally characterized mononuclear high-spin cobalt(II) complex with a pyridine amide ligand. The magnetic moments of 1 and 2 at 300 K reveal that the compounds are paramagnetic (1 has S = 3/2 and 2 has S = 1/2), both as solids and in dmf solution. Temperature dependent magnetic susceptibility measurements confirmed their spin state. The stereochemistry of the cobalt(II) centre in 1 does not change to any measureable extent on dissolution in dmf (cf. solid and solution state absorption spectra). The geometry of the copper(II) centre in 2 observed in the solid state is not retained in dmf solution (absorption spectra), changing to a tetragonal stereochemistry. Cyclic voltammetric measurements (dmf solution; glassy carbon electrode) on 1 reveal an oxidative response at 0.48 V vs. saturated calomel electrode (SCE) and a reductive response at –1.66 V corresponding to CoIII–CoII and CoII–CoI redox couples, respectively. For 2 the CuII–CuI process was observed at –0.53 V vs. SCE.

The reaction chemistry of a technetium(I) nitrosyl complex with potentially chelating organohydrazines: the X-ray crystal structure of [TcCl 2(NO) (HNNC 5H 4N) (PPh 3)

The reaction of the nitrosyl complex [TcCl 2(NO)(MeCN))(PPh 3) 2] with 2-hydrazinopyridine dihydrochloride in refluxing MeOH gives the purple complex (TcCl 2(NO) (HN)NC 3H 4N) (PPh 2] ( 1) in which the neutral bidentate organodiazene ligand has replaced the acetonitrile and a phosphine ligand. The IR spectrum of 1 shows a very strong absorption at 1732 cm −1 attributed to v(NO). The FAB(+) mass spectrum of 1 displays the protonated parent ion at 570 m/z and the fragment generated by the loss of a chloride ligand from the parent ion at 533 m/ z. The 1H NMR spectrum of this diamagnetic complex displays the signal from the α-nitrogen-proton of the pyridyldiazene at 17.95 ppm as well as the aryl-protons. The X-ray crystal structure of this complex shows a distorted octahedral coordination geometry. The TcN bond length of 1.752(4) Å is consistent with the multiple bonding expected for the linearly bonded nitrosyl ligand. The TcNO bond angle is 175.1(4)°. The NTcN bond angle of the chelated pyridyldiazene ligand is 73.1(2)°, which reflects the small bite angle imposed by the five-membered chelate ring of this ligand. The reaction of the nitrosyl complex [TcCl 2(NO)(MeCN))(PPh 3) 2] with 2-hydrazino-4-trifluoromethylpyrimidine in refluxing dichloromethane gives the neutral Tc(I) complex [TcCl(NO) (NNC 4H 2N 2R)(PPh 3) 2] in which the anionic bidentate organodiazenido ligand has replaced the acetonitrile and a chloride ligand. The IR spectrum of 2 shows a very strong absorption at 1717 cm −1 attributed to v(NO). The FAB(+) mass spectrum of 2 displays the parent ion at 886 m/ z as well as the fragment generated by the loss of the diazenido ligand at 688 m/ z. The peak associated with the loss of a phosphine ligand from the parent ion at 604 m/ z is also evident.

Electronic band assignments of high- and low-spin Ni[R′ 2P(NR) 2] 2

Absorption spectra in the VIS and NIR region of the title compounds have been measured from KBr discs at temperatures down to 2 K. The paramagnetic complexes ( R′=phenyl,R= i propyl or methyl 3 Si) have pseudo-tetrahedral coordination in the crystal and the similar diamagnetic complex Ni[ i pr 2P(Nmethyl) 2] 2 is almost planar. All chelates have a small bite angle (76–78°). The electronic spectra are close to what is expected from distorted tetrahedral and quadratic Ni(II) complexes, respectively. Angular overlap model calculations, carried out using valence angles from the X-ray structure analysis, allow assignments of the measured peaks to electronic levels in D 2 d or D 2 point symmetry. The model parameters obtained compare well with those of other NiN 4 complex chromophores.

Specific Chelate Tuning of the Substitution Kinetics of Platinum(II) Complexes in Aqueous Solution

Both reaction steps observed for the substitution of water by thiourea in the complexes [Pt(en)(OH2)2]2+ and [Pt(phen)(OH2)2]2+ (en = ethylenediamine, phen = 1,10-phenanthroline) were investigated under pseudo-first-order conditions using the stopped-flow technique. The substitution of the second water molecule in each complex was also studied under high pressure. The observed pseudo-first-order rate constants kobs (s−1) obeyed the equation k1,2obs= k1,2[tu] (tu = thiourea), where “1” and “2” refer to the first and the second substitution reactions, respectively. Kinetic parameters associated with the substitution process are: k1en (25.0°C, pH = 3.0, I = 0.1 M) = 25.6 M−1 s−1, ΔH# = 51 kJ mol−1, ΔS# = −48 J K−1 mol−1; k2en (same conditions) = 12.1 M−1 s−1, ΔH# = 30 kJ mol−1, ΔS# = −124 J K−1 mol−1, ΔV# = −7 cm3 mol−1; k1phen (25.0°C, pH = 1.0, I = 0.1 M) = 2900 M−1 s−1, ΔH# = 41 kJ mol−1, ΔS# = −41 J K−1 mol−1; k2phen (same conditions) = 1170 M−1 s−1, ΔH# = 37 kJ mol−1, ΔS#= −61 J K−1 mol−1, ΔV# = −5 cm3 mol−1. The temperature and pressure dependence of all the processes studied suggest an associative substitution mechanism. The hydroxo-bridged dinuclear complex [{Pt(phen)(μ-OH)}2]2+ is formed from [Pt(phen)(OH2)2]2+ in aqueous solution unless the solution is very dilute and highly acidic. The X-ray structure of [{Pt(phen)(μ-OH)}2](F3CSO3)2 · 2 H2O was determined. It belongs to the triclinic space group P1­ and has one formula unit in the unit cell. The unit cell dimensions are a = 7.126(5), b = 9.665(5), c = 12.774(7) Å; α = 71.85(5), β = 85.52(5), γ = 73.12(5) deg; V = 799.9(8) Å3. The structure was solved with the Patterson method and refined to R = 0.061. A square planar coordination of the platinum centers is observed, with no deviations from planarity but distortions due to the small bite angle of phen and the four-membered ring. No significant lengthening of the Pt−O bond [mean value: 2.03(1) Å] is observed in comparison with [{Pt(NH3)2(μ-OH)}2]2+.

Specific Chelate Tuning of the Substitution Kinetics of Platinum(II) Complexes in Aqueous Solution

Both reaction steps observed for the substitution of water by thiourea in the complexes [Pt(en)(OH2)2]2+ and [Pt(phen)(OH2)2]2+ (en = ethylenediamine, phen = 1,10-phenanthroline) were investigated under pseudo-first-order conditions using the stopped-flow technique. The substitution of the second water molecule in each complex was also studied under high pressure. The observed pseudo-first-order rate constants kobs (s−1) obeyed the equation k1,2obs= k1,2[tu] (tu = thiourea), where “1” and “2” refer to the first and the second substitution reactions, respectively. Kinetic parameters associated with the substitution process are: k1en (25.0°C, pH = 3.0, I = 0.1 M) = 25.6 M−1 s−1, ΔH# = 51 kJ mol−1, ΔS# = −48 J K−1 mol−1; k2en (same conditions) = 12.1 M−1 s−1, ΔH# = 30 kJ mol−1, ΔS# = −124 J K−1 mol−1, ΔV# = −7 cm3 mol−1; k1phen (25.0°C, pH = 1.0, I = 0.1 M) = 2900 M−1 s−1, ΔH# = 41 kJ mol−1, ΔS# = −41 J K−1 mol−1; k2phen (same conditions) = 1170 M−1 s−1, ΔH# = 37 kJ mol−1, ΔS#= −61 J K−1 mol−1, ΔV# = −5 cm3 mol−1. The temperature and pressure dependence of all the processes studied suggest an associative substitution mechanism. The hydroxo-bridged dinuclear complex [{Pt(phen)(μ-OH)}2]2+ is formed from [Pt(phen)(OH2)2]2+ in aqueous solution unless the solution is very dilute and highly acidic. The X-ray structure of [{Pt(phen)(μ-OH)}2](F3CSO3)2 · 2 H2O was determined. It belongs to the triclinic space group P1­ and has one formula unit in the unit cell. The unit cell dimensions are a = 7.126(5), b = 9.665(5), c = 12.774(7) A; α = 71.85(5), β = 85.52(5), γ = 73.12(5) deg; V = 799.9(8) A3. The structure was solved with the Patterson method and refined to R = 0.061. A square planar coordination of the platinum centers is observed, with no deviations from planarity but distortions due to the small bite angle of phen and the four-membered ring. No significant lengthening of the Pt−O bond [mean value: 2.03(1) A] is observed in comparison with [{Pt(NH3)2(μ-OH)}2]2+.

The synthesis and characterization of a technetium nitrosyl complex with cis-{2-pyridyl,diphenylphosphine} coligands. The X-ray crystal structure of [TcCL 2(NO) (pyPPh 2- P, N) (pyPPh 2- P)

The reaction of the Tc(II) nitrosyl complex (Bu 4N) [Tc(NO)Cl 4] with excess pyPPh 2 in refluxing MeOH gives the bis-pyridyl-diphenylphosphine complex [TcCl 2(NO)(pyPPh 2- P, N) (pyPPh 2- P)]. The IR spectrum of the crystalline product shows a medium intensity band at 1092 cm −1 and a very strong band at 1732 cm −1 which is assigned to v(Tc=N) from the nitrosyl core. The FAB(+) mass spectrum shows the protonated parent ion of 725 m/ z and the peak associated with the loss of a chloride ligand from the parent ion of 690 m/ z. The 1H NMR spectrum of the diamagnetic Tc(1) complex shows an extended series of multiples in the aryl region between 7.0 and 9.15 ppm. The X-ray crystal structure shows an unusual cis arrangement of these bulky phosphine ligands with one of these phosphine ligands coordinated in a bidentate manner. The Tc-N bond length of 1.743(5) Å is consistent with the multiple bonding expected for the linearly bonded nitrosyl ligand. The Tc-N-O bond angle of 177.2(5)° reflects the sp hybridization of the nitrosyl-nitrogen atom. The Tc-P bonds are 2.400(2) and 2.405(2) Å, which are unexceptional, as are the Tc-Cl bonds of 2.447(2) and 2.441(2) Å. The coordination geometry of this complex is best described as a very distorted octahedron. The P-Tc-N bond angle of the chelated pyridyl phosphine ligand is 66.1(1)°, which reflects the very small bite angle imposed by the four-membered chelate ring of this phosphine. This is compensated for by a large P-Tc-P angle of 107.82(5)°, imposed by the cis-phosphine coordination of these bulky tri-aryl phosphine ligands. Crystal data for C 34 5H 29 Cl 4 N 4 OP 3Tc: triclinic space group P1, a=9.8440(3), b=13.4854(5), c=14.2401(5) A ̊ , α=106.406(1), β=96.013(1), γ=92.792(1) 2 V=1797.35(11) A ̊ 3 , with D calc=1.419 g cm −3. Structure solution based on 5018 observed reflections converged at R=5.28%, for (1>2 σ(1)); GOF=1.73.

Crystal structures of a series of Co II, Cu II and Zn II complexes of 4′-(3,4-dihydroxyphenyl)-2,2′ : 6′,2″-terpyridine and 4′-(3,4-dimethoxyphenyl)-2,2′:6′,2″-terpyridine

The crystal structures of the bis(terpyridyl)-metal(II) complexes (Co(L 1) 2][PF 6] 2 · 2.5MeCN, [Co (L 2) 2][PF 6] 2 · 3dmf, [Cu(L 2) 2][PF 6] 2 · 2.5MeCN, and [Zn(L 2) 2][NO 3] 2 · 3dmf are reported, where L 1 is 4′-(3,4-dihydroxyphenyl)-2,2′ : 6′,2″-terpyridine and L 2 is 4′-(3,4-dimethoxyphenyl)-2,2′: 6′,2″-terpyridine. The two Co II complexes and the Cu II complex all show elongation along one axis in addition to the normal tetragonal compression imposed by terpyridyl chelates; this is ascribed to the Jahn-Teller effect, in the case of the Co II complexes arising from the presence of a significant proportion of the low-spin state being present at the temperature used for the structural determination (173 K). The Zn II complexes are the first structurally characterised bis(terpyridyl)-Zn II compounds. These do not show the elongation along one axis that was apparent in the Co II and Cu II structures. The relatively small bite angles for the terpyridyl chelates (ca. 150°, compared to ca. 160° for the first three complexes), results in a greater distortion away from regular octahedral geometry, reflecting the absence of stereoelectronic requirements for Zn II compared to Co II and Co II.