Lewis-Base Adducts of Lead(II) Compounds. XVII. Synthetic and Structural Studies of Some 1:1 Adducts of 2,2':6,2'-Terpyridine With Lead(II) Salts

Abstract

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for 1:1 adducts of 2,2':6',2"-terpyridine (' tpy ') with the lead(II) oxoanion salts perchlorate, nitrate and nitrite, ( tpy ) Pb ( oxoanion )₂. All structures are monoclinic, C2/c, Z = 4, with approximate ranges a from 9 to 11 Ǻ, b from 16 to 20 Ǻ, c from 9.8 to 13.8 Ǻ, β from 113 to 130° and V from 1650 to 1850 Ǻ³. In all cases the lead(II) atoms are disposed on crystallographic 2 axes which also pass through the axis of the central tpy ring; a pair of symmetry related oxoanions link successive lead atoms in a one-dimensional polymeric chain parallel to the ac cell diagonal, one pair of oxygen atoms functioning as an O,O'-bidentate with another oxygen (replaced by the nitrogen in the nitrite) bridging to the adjacent lead atom; the third anionic oxygen atom in the nitrate is replaced by a water molecule in the nitrite, which thus becomes a monohydrate. Residuals were 0.030, 0.034 and 0.040 for 2122, 1564 and 2059 independent 'observed' (I > 3σ(I)) reflections respectively. Also recorded are the syntheses and room-temperature single-crystal X-ray structure determinations for 1:1 aducts of 2,2':6',2"-terpyridine with lead(II) chloride, bromide and iodide, the chloride and bromide being hydrated. ( tpy )PbCl₂.H₂O is monoclinic, P 2₁/c, a 8.938(1), b 15,210(7), c 13.414(3) Ǻ, β 115.17(1)°, Z = 4 f.u .; R was 0.036 for N_o = 3346 independent, 'observed' reflections. The complex is centrosymmetric, binuclear [( tpy ) (H₂O)( Cl ) Pb (μ- Cl )₂Pb( Cl )(OH₂)( tpy )], with the two lead atoms linked by bridging chlorine atoms; the lead atoms are seven-coordinate N₃,O,ClPb(μ- Cl )₂. The bromide ( tpy )PbBr₂.2/3H₂O, triclinic, Pī, a 12.360(6), b 12.452(4), c 18.372(6) Ǻ, α 108.31(3), β 109.44(3), γ 90.56(3)°, Z = 6 f.u ., R being 0.046 for N_o 7282, is in fact trinuclear [Pb₃Br₆( tpy )₆].2H₂O, a novel and elegant oligomer with quasi-2 symmetry in which a central lead atom (on the quasi-2 axis) is seven-coordinated [( tpy ) Pb (μ-Br)₄] with the associated bromides bridging to a pair of peripheral lead atoms, also seven coordinated, [( tpy )(Br) Pb (μ-Br)₃]. Unsolvated ( tpy )PbI₂, triclinic, Pī , a 10.834(3), b 9.023(3), c 8.906(2) Ǻ, α 80.34(2), β 89.40(2), γ 79.78(2)°, Z = 2 f.u ., R 0.031 for N_o 2347 is, like the chloride, centrosymmetric binuclear, [( tpy )(I) Pb (μ-I)₂Pb(I)( tpy )], but with the lead(II) now six-coordinate N₃(I) Pb (μ-I)₂. In both chloride and iodide, the tpy plane is approximately normal to the Pb ... Pb line with the water molecule of the chloride approximately trans to the central tpy nitrogen; in the iodide that site is occupied by the terminal halide.