Lewis-Base Adducts of Lead(II) Compounds. X. Synthetic and Structural Studies of Some 1:1 Adducts of 'tet-b' With Lead(II) (Pseudo-)Halides

Abstract

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for 1 : 1 adducts of (7R*,14R*)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (' tet -b') with a variety of lead(II) salts. [( tet -b)PbCl₂] is monoclinic, P 2₁/c, a 7.183(3), b 12.425(2), c 24.418(2) Ǻ, β 95.32(3)°, Z = 4; conventional R on |F| was 0.044 for 3188 independent, 'observed' (I > 3σ(I)) reflections. [( tet -b)PbI₂] is monoclinic, P 2₁/c, a 19.920(5), b 7.772(5), c 15.605(6) Ǻ, β 108.39(2)°, Z = 4; R 0.051 for N_o 2507. [( tet -b) Pb (NCS)₂] is orthorhombic, P 2₁2₁2₁, a 36.99(1), b 8.996(5), c 6.964(3) Ǻ, Z = 4; R 0.043 for N_o 2100. All are discrete mononuclear [( tet -b)PbX₂] entities in which the macrocyclic N₄ ligand occupies one 'face' of the N₄PbX₂ coordination sphere, the thiocyanate ligands being N-bonded, with Pb -N-C angles of 116(2) and 118(1)°; interesting hydrogen-bonding interactions are found, columns of molecules being formed by way of hydrogen bonding between the coordinated (pseudo-)halides and the NH hydrogen atoms which project to the 'rear' face of the ligand of the next molecule, opposite the metal. In contrast to these, the bromide analogue, monoclinic, P2₁, a 9.342(3), b 12.720(5), c 18.845(5) Ǻ, β 103.17(2)°, Z = 4, R 0.035 for N_o 3593, is best formulated as [( tet -b) PbBr ] Br, one only of the bromide entities being bound to the lead, the other being fully dissociated by hydrogen bonding/ion pairing to the 'rear' side of adjacent ligands , forming hydrogen-bonded sheets rather than columns. This formulation has been extended to provide a description of an analogous mixed chloride- perchlorate 'double salt', [( tet -b) PbCl ] (ClO₄).CH₃OH, which is orthorhombic, P 2₁2₁2₁, a 19.475(2), b 18.73(1), c 6.820(2) Ǻ, Z = 4, R 0.054 for N_o 3075. However, another double salt, modelled in refinement as Pb ( tet -b)Cl_0.5(ClO₄)_1.5.H₂O, orthorhombic Pnma , a 20.640(5), b 26.16(1), c 8.937(4) Ǻ, Z = 4 dimers , R 0.074 for N_o 1769, is in this case more appropriately described as [( tet -b) Pb (OClO₂O)₂Pb( tet -b)] (ClO₄) Cl.H₂O with perchlorate rather than halide coordinated, and an incipiently dimeric cation, as in the parent [( tet -b) Pb (OClO₃)]₂ (ClO₄)₂.2H₂O.