E.Donald McKenzie

Metal(III) compounds of potentially septadentate [N4O3] ligands. Part II. Crystal and Molecular structures of [M(C27H24Cl3N4O3]·3H2O (M = Cr, Mn)

The three dimensional X-ray structural analyses are reported of the chromium(III) and manganese(III) compounds of the trianionic Schiff base ligand derived from tris(2-aminoethyl)amine and three mol of 5-chlorosalicylaldehyde. Both are isomorphous with the previously reported Fe III compound: space group Ia 3 (No. 206) a = 22.521(2) A [Cr], and 22.490 A [Mn]. Data were collected by diffractometer {958 independent reflections for Cr (Cu-Kα radiation), and 852 for Mn (Mo-Kα radiation)}, and the structures were refined by block-diagonal least-squares to final Rs of 0.072 [Cr] and 0.050 [Mn]. Both are essentially octahedral [M(N 3 O 3 ] species, lying on three-fold crystallographic axes, and the Mn compound provides an unusual example of an undistorted octahedral d 4 system. Bond-lengths in the coordination polyhedra are: CrO 1.979(6), CrN 2.137(7), MnO 1.965(3), and MnN 2.137(4) A . Non-bonded metal to apical (tertiary) nitrogen distances are hardly different from that found in the isomorphous Fe III compound: MN = [Cr] 3.229(8), [Mn] 3.229(4), and [Fe] 3.260(4) A .

Copper(II) compounds with the potentially quinquedentate ligand N,N′-bissalicylidene-1,5-diimino-3-azapentane, including an X-ray structure analysis of [Cu2(C18H19N3O2)2]·2C3H6O

Abstract The reaction of copper(II) acetate with the Schiff base ligand of the title gives mixed green polymeric materials. ‘Recrystallisation’ of these from various solvents gives crystalline solvates of a green dimeric copper(II) compound, the structure of which has been determined by a three-dimensional X-ray analysis of one crystalline form of the acetone solvate. Crystals of the title compound are monoclinic: a = 12.86(1), b = 16.74(2), c = 9.86(1) A, β = 105.11(1)°, space group P21/c. Using 3555 independent reflections, obtained on a 2-circle diffractometer, the structure was solved by conventional Patterson and Fourier methods, and refined by block-diagonal least squares to R = 0.043. The two multidentate ligands bridge two five-coordinate copper atoms in a centrosymmetric molecule. The salicylaldiminato moieties from the different ligands are bidentate to each copper [CuO(1) = 1.936(3); CuO(2) = 1.975(3); CuN(1) = 1.962(3); and CuN(3) = 1.984(3) A] and the fifth ligand for each copper is the secondary amine nitrogen at a longer distance of 2.405(3)A.

A carbinolamine bonded to copper(II): Crystal and molecular structure (X-ray Analysis) of dibromo-[2-picolyl-(2-pyridylmethanol)methylamine] copper(II) Monohydrate

Abstract Reaction of 2-picolylmethylamine with CuBr2 in water in an open vessel gives, together with other products, green crystals of the title compound, the structure of which has been determined by a three-dimensional X-ray structural analysis. Crystals were monoclinic with a = 8.38(1), b = 27.60(3), c = 7.69(1) A, and β = 114.6(1]°, space group P21/c and Z = 4. The structure was solved by conventional Patterson and Fourier techniques, and was refined anisotropically by least-squares methods, using 1098 unique reflections to a final R of 0.070. Data were obtained photographically, with intensities determined on an integrating microdensitometer. The analysis shows each copper atom to be five-coordinate [Cu(N3)Br2], intermediate in structure between the square pyramidal and trigonal bipyramidal extremes. The metal is bonded to a terdentate ligand which it an unusual carbinolamine formed by the condensation of one mol of 2-picolylmethylamine with a mol of pyridine-2-aldehyde, formed by oxidative de-amination of the amine. Bond lengths in the co-ordination polyhedron are: CuBr(1) 2.598(3), CuBr(2) 2.436(3), CuN(pyridyl) 1.98(1) (av), and CuN (tertiary amine) 2.07(1) A. The water molecule is hydrogen-bonded to the alcohol group of the [N3] ligand, and joins adjacent molecules through H-bonds to their Br(1)s.

Metal compounds of tetra-amines with terminal pyridyl residues. Crystal and molecular structures of [M(C15H20N4)](ClO4)2 {M = Pd, Cu}

Abstract Single crystal X-ray analyses of 1,7-bis(2-pyridyl) 2,6-diazaheptanecopper(II) perchlorate and -palladium(II) perchlorate have been carried out. Both compounds crystallize in orthorhombic unit cells with Z = 8: for the Cu compound, space group Pnma with dimensions a = 13.746(1), b = 26.388(2), c = 11.225(1) A; and for the Pd compound, space group Pmn21 (only 39 weak reflections break the condition k ≠ 2n for hkO, which would allow the same space group as the Cu analogue) with dimensions a = 26.97(1), b = 13.81(1), c = 10.90(1) A. The structures were solved by the heavy atom method and refined by least-squares techniques to R = 0.109 for 925 unique diffractometer data for the Cu compound and to R = 0.101 for 2190 unique photographic data for the Pd analogue. All atoms were placed in the Pd structure, but the Cu structure showed disorder in position and occupancy of many perchlorate oxygen sites, and a smaller averaged disorder in the positions of some of the atoms in the cations. The [MN4] polyhedra are essentially planar, but with some tetrahedral twist and a twist-boat conformation in the trimethylene chelate rings - both of which are a response to the steric preferences of the amine ligand. Perchlorate oxygens approach the metals in axial (tetragonal) sites; between 2.93 and 3.23 A for Pd, but closer at 2.64 and 2.70 A for Cu. Differences in the i.r. spectra in the vN-H region appear now to result from the observed proximities of perchlorate oxygens to the NH groups. However, there is no evidence for any water in a regular pattern in the crystals, which could account for i.r. bands observed at 3620 and 3540 cm−1.

Nickel(II) compounds of three homologous linear tetra-amines, especially solvent effects and configuration

Abstract A comparative study has been made of the 1:1 nickel(II) compounds of three homologous linear tetraamines: 1,4,7,10-tetraazadecane(trien), 1,4,8,11- tetraazaundecane(2,3,2-tet), and 1,5,8,12-tetraazodecane(3,2,3-tet). A range of solid compounds Ni(tetraamine)X 2 (X = Cl, Br, I, NCS, NO 2 , NO 3 , Clo 4 ), a number of which are new, has been prepared from 2,3,2-tet and 3,2,3-tet. These include the structural isomers yellow low-spin [Ni(3,2,3-tet)]I 2 ] and lilac high-spin trans -[Ni(3,2,3-tet)]I 2 ]. The high-spin species have a trans octahedral configuration, except for [Ni(2,3,2-tet)NO 3 ]NO 3 , which appears to have a chelating nitrate. In solution in water, DMF, and DMSO two equilibria of these compounds have been studied under varying conditions: (a) the cis ⇄ trans equilibria of the high-spin [Ni(N 4 )(S) 2 ] 2+ species (S = solvent); and (b) high spin octahedral ⇄ low-spin planar equilibria. It is shown for the first time that equilibria (a) occur in such solutions for both 2,3,2-tet and 3,2,3-tet. The trans isomers are preferred over cis in the orders: (i) (for solvent) H 2 O > DMF > DMSO; and (ii) (for the amines) 3,2,3-tet > 2,3,2-tet ⪢ trien. In concentrated LiNO 3 and LiClO 4 , Ni(trien) 2+ , but not the others, forms high spin cis -[Ni-(N 4 )O 2 ] species which apparently have a chelating anion. For equilibria (b) (the singlet ⇄ triplet equil.) the planar low-spin species are preferred in the order 2,3,2-tet > 3,2,3-tet > trien — an order different from that observed in (a). Difficulties in defining ϵ max for these low-spin species, and hence in quantifying the equilibria are discussed with evidence for the complication. The observations on both equilibria can be rationalised by reference to the steric effects of the amines: 3,2,3-tet has a greater preference thatn 2,3,2-tet for trans high-spin isomers, but it can less easily accomodate to the shorter NiN bond lengths in the low-spin species.

The slow isomerisation of a high-spin [Ni(tetraamine)(DMSO)2]2+ cation

In DMSO solution the [Ni(2, 3, 2-tet)DMSO)2]2+ cation (2, 3, 2-tet = 1, 4, 7, 11-tetraazaundecane) undergoes a remarkably slow trans cis isomerisation: the initially trans cation converts to an equilibrium mixture which is mainly cis.kobs(298) = 1.92 × 10−5 sec− (t1/2 ≈ 14 hr), Keq ≈ 5, kobs(138) = 4.89 ×10−5 sec−1, ΔH≠ = 8.2 (±0.5) kcal mol−1, ΔS≠ = −52.0 (±2.0) cal deg− mol−, and Ea = 8.8 (±0.5) kcal mol−1. Added water or dimethylsulphone accelerate the reaction, which seems to be unique among such tetraamine compounds. The slowness probably results from a uniquely ordered solvent shell.

Cobalt(III) compounds of carbanions and their reactivity. Part III. Crystal and molecular structure of trans-3,3,4,4-tetracyano-2-phenylcyclopentylbis(dimethylglyoximato)imidazolecobalt(III)

Abstract Cyrstals of the title compound, obtained from tetracyanothylene and trans -cinamylbis(dimethylglyoximato)cobalt(III), were triclinic with a = 11.869(8), b + 12.892(8), c = 10.134(9) A, α = 79.90(1), β = 72.44(2), γ = 71.75(1)°, spcae gropu P 1 , and Z = 2. The structure was solved by conventional Patterson and Fourier techniques, and refined anisotropically by block-diagonal least-squares methods to a final R of 0.046. The analysis shows the cyclopentyl carbanion ligand to have a trans arrangement of substituents. As unusually lon CoC distance of 2.049(7) A is opposed by an unsusually short trans CoN bond to imidazole of 2.00(7) A. The phenyl substituent of the carbanion ligand appears to be π-bonded to a glyoximato moiety. The two short hydrogen bonds between oxygens of opposing glyoximato units are different: one, at 2.455(10) A, is near the lower limit of observed hydrogen bonds and the other, at 2.518(9) A, is the longest of any presently known in such ‘cobaloxime’ structures. The latter is associated with another hydrogen bond between one of the oxygens and NH of an imidazole, and with the π-bond to the phenyl.

Structure and redox properties of some planar [M11N4] chelate compounds of cobalt and nickel. Part III. Crystal and molecular structure of bis[cyclohexane-1,2-bis-2′-pyridylhydrazonato]-dinickel(II), 2-benzene

Abstract The structure of the little compound has been determined by a three-dimensional X-ray structural analysis. Crystals were monoclinic with a = 9.97(1), b = 21.77(1), c = 19.74(2) A, β = 102.0(1)°, space group P21/c, and Z = 4. The structure was solved by conventional Patterson and Fourier techniques, and was refined anisotropically by block-diagonal least-squares methods by visual estimation of photographs, to a final R of 0.085. The analysis shows an unusual dimeri structure in which two nickel atoms share the two quadridentate ligands. Each nickel atom has an essentially four co-planar coordination polyhedron made up from three nitrogens from one ligand and a pyridyl nitrogen of the other ligand {pyridyl} . p ]The NiN distances are (a) (terminal pyridyl) 1.89(1) A; (b) (bridging pyridyl) 1.94(1) A; and c (hydrazone) 1.84(1) A. There are two NCN groups bridging the two nickel atoms. The coordination planes of the nickels are inclined at 34° to one another. The relatively short NiNi distance of 2.809(2) A is indicative of a significant metalmetal bond. Some disorder was evident in the positions of some of the atoms of the cyclohexyl moieties, and there was only partial occupancy of one of the three independent sites for benzene molecules.

Crystal and molecular structure of a nickel(II) compound derived from 2-methylpropane-1,2-diamine: [Ni(C18H21N4)]ClO4

Crystal of the title compound are monoclinic, a = 19.25(4), b = 13.91(1), c = 14.66(3) A, β = 94.56(2)°, space group B21/a. A three dimensional X-ray analysis of the structure was made with counter data (2244 independent reflections). The structure was solved by conventional Patterson and Fourier methods and refined by block-diagonal least-squares to R 0.058. The monocation contains an [NiN4] four co-planar polyhedron with NiN distances of 1.848(6) A (anionic amido), 1.875(6) and 1.880(5) A (azomethine) and 1.928(6) A (primary amine). The ligand is an unusual Schiff base combination of a dimer of 2-aminobenzaldehyde with a terminal diamine. The 1H n.m.r spectra of the salts of this cation are discussed in the light of this structure, and ‘covalent hydration’ is suggested as an explanation of the observed differences in aqueous solution.

Reactions of copper(II) and nickel(II) compounds of 6-methyl-2-picolylamine with acetone, including and x-ray structural analysis of [Ni(C20H28N4)(NO3)]NO3

The reaction with acetone of nickel(II) and copper(II) bis-chelated compounds of 6-methyl-2-pyridylmethylamine gives compounds of the quadridentate [N4] ligand 2,6-diaza-1,7-bis-(6′-methyl-2′-pyridyl)-3,5,5-trimethyl-hept-2-ene(Q). In the nickel series also, a bis-chelated perchlorate of the terdentate ligand 2-aza-1-(6′-methyl-2′-pyridyl)-3-methyl-hex-2-ene-5-one was obtained. In the copper series, five-coordinate species [Cu(Q)X]X (X = Br, I, NCS) and [Cu(QX]ClO4 (X = Cl) were isolated. If left in acetone, these undergo further reaction, with increasing ease in the order Cl < Br < I. An intermediate formation of a transient brown colour suggests the possible involvement of a copper(I) intermediate. The nature of the products was established by an X-ray analysis of the structure of [Ni(Q)NO3]NO3. Crystals are orthorhombic, a = 20.36(2), b = 13.38(1), c = 8.226(5) A, space group Pna21. Using two-circle diffractometer data (1598 reflections), the structure was solved by Patterson and Fourier methods, and refined by block diagonal least-squares methods to a final R of 0.030. The expected quadridentate ligand was found in the cis-β configuration about the metal, with coordination sphere completed by a bidentate nitrate. Bond-lengths and angles within the molecular cation were unexceptionable considering the small ‘bite’ of the chelated nitrato group of only 59°.