Walter Purcell

Identification of different Cr(III) nta complexes: crystallisation of Cs2[Cr2(nta)2(μ-OH)2]·4H2O in two space groups

Abstract Cs2[Cr2(nta)2(μ-OH)2]·4H2O (nta=nitrilotriacetate) crystallises in two different space groups due to a slight variation in pH of the reaction mixtures. The structures of Cs2[Cr2(nta)2(μ-OH)2]·4H2O have been determined from three-dimensional X-ray diffraction data. The complex crystallises in the tetragonal, I41/a (I) and monoclinic, P21/c (II), space groups. The two hydroxo groups bridge the two Cr centres with OH–Cr–OH angles of 81.5(3)° (I) and 82.08(10)° (II), respectively. The tetradentate nta ligand completes the octahedral geometry around the Cr centre. The Cr–OH bonds are 1.942(7) and 1.961(6) A for (I) and 1.987(2) and 1.991(1) A for (II). The Cr–N and Cr–O(av) are 2.048(9) and 1.967(8) A for (I) and 2.061(3) and 1.975(2) A for (II), respectively.

The crystal structure of tetraethylammonium aquatetracyanooxorhenate(V)

SummaryThe crystal structure of the tetraethylammonium salt of [ReO(H2O)(CN)4]− has been determined from threedimensional x-ray diffraction data. The light blue crystals are monoclinic, space group P21/m witha=8.760(1),b=9.518(5),c=11.718(1) Å, β=102.63(1)o with two molecules per unit cell. The final R value using 2009 observed reflections and anisotropic thermal parameters for all the non-hydrogen atoms was 0.038. The [ReO(H2O)(CN)4]− ion has a distorted octahedral geometry with the rhenium atom displaced by 0.30 Å out of the plane formed by the four carbon atoms of the cyano ligands towards the oxo ligand. Bond distances: Re=O=1.667(8), Re−OH2=2.142(7) and Re−C (average)=2.11(1) Å.

Kinetic study of the reaction betweentrans-tetracyanodioxorhenate(V) and thiocyanate ions

SummaryThe kinetics of the reaction between NCS− and the diprotonated forms of [ReO2(CN)4]3− have been studied in theca. 1 to 3 pH range. This study showed that the diprotonated form [ReO(OH2)(CN)4]−1 is the only reactive species and that only the aqua ligand is substituted by the thiocyanate ions according to the following reaction:

Kinetics of the substitution reaction between aquaoxotetracyanomolybdate(IV) and cyanide/hydrogen cyanide

[ReO(OH_2 )(CN)_4 ]^{1 - } + NCS - [\operatorname{Re} O(NCS)(CN)_4 ]^{2 - } + H_2 O

Crystal structure of tetraphenylarsonium aquatetracyanonitridorhenate(V), (AsPh4)2 [ReN(H2O)(CN)4]·5H2O

The k1 and k−1 values are 3.48(4)×10−3 M−1 s−1 and −3(2)×10−5 s−1 respectively at 25°C. A dissociative activated substitution process is proposed.

Synthesis and characterisation of water soluble Pt(II) complexes of 1,3,5-triaza-7-phosphaadamantane (PTA). Crystal and molecular structure of {cis-[PtCl2(PTA)2]}2 · H2O

Abstract The crystal structure of Cs2[Co2(nta)2(μ-OH)2] · 4H2O (nta = nitrilotriacetate) has been determined from three-dimensional X-ray diffraction data. Two hydroxo groups act as bridging groups between the two Co metal centres. The CoOH bond distances are 1.899(5) and 1.897(5) A, respectively and the CoOHCo bond angles 98.2(2)°. The nta ligand acts as a tetradentate ligand and bonds with a nitrogen as well as three oxygen atoms to the Co metal centre. The CoN and CoO(av) bonds are 1.922(6) and 1.895(5) A, respectively. (C10H10H3)2[CoCl4] consists of discrete monoprotonated 2,2′-iminodipyridinium cations and CoCl42− anions. The anions assume a regular tetrahedral geometry, with the ClCoCl bond angles varying between 107.34(10) and 112.07(10)°. The CoCl bond distances are 2.270(2) and 2.282(2) A, respectively. The two pyridine rings in the cation assume an almost planar orientation with a derivation of 7.7(6)° for the dihedral angle between the two ring systems. The planar orientation can be attributed to weak hydrogen bonding between the unprotonated nitrogen atom of the one pyridine ring and the proton bonded to the other nitrogen atom on the adjacent ring.

Kinetic study of the reaction betweentrans-aquanitridotetra-cyanorhenate(V) and different cyanide species

Abstract The kinetics of the substitution reaction between aquaoxotetracyanomolybdate (IV) ions and CN− and HCN, as an important intermediate step in the formation of the [Mo(CN)8]4− complex, was studied by stopped-flow spectrometry. The aqua ligand in the [MoO(H2O)(CN)4]2− complex is substituted by both CN− ions and hydrogen cyanide according to the reaction: At 15.0°C and μ = 1.0 M (KNO3) the equilibrium, forward and reverse rate constants of the reaction with CN− ions were determined as 92(5) M−1 s−1 and 0.87(3) s−1, and for HCN as 3(1) M−1, 458(5) M−1 s−1 and 140(30) s−1, respectively. Coordination of the HCN to the metal centre results in a decrease in the pKa value of hydrogen cyanide by approximately 1.5 pH units to ca 7.6(2).

Kinetic and equilibrium study of substitution reactions oftrans-tetracyanodioxorhenate(V) ions with monodentate nucleophiles

SummaryThe crystal structure of (PPh4)2[ReO(OH)(CN)4]·5H2O has been determined from three-dimensional x-ray diffraction data. The light brown crystals are monoclinic, space group P21/n, with cell dimensionsa=16.753(2),b=19.928(2),c=15.338(2) Å and β=101,894(1)°,z=4, Dm=1.45(1) g cm−3. The anisotropic refinement of the 6088 observed reflections converged to R=0.077.The [ReO(OH)(CN)4]2− ion has a distorted octahedral geometry. Bond distances: Re =1.70(1), Re−OH=1.90(1) and ReℑCav=2.12(2) Å. The Re atom is displaced by 0.08 Å out of the plane formed by the four carbon atoms towards the terminal oxo ligand.