Metal complexes of molecular clefts. The synthesis and X-ray crystal structures of a mononuclear barium and four binuclear silver(I) complexes of bibracchial tetraimine Schiff-base macrocycles

Abstract

Mononuclear barium and binuclear silver(I) complexes of bibracchial tetraimine Schiff-base macrocycles L¹—L⁴ derived from the ‘2 + 2’ condensation of 2,6-diacetylpyridine and the functionalised triamines N,N-bis(2-aminoethyl)-2-(aminomethyl)pyridine, N,N-bis(3-aminopropyl)-2-(aminomethyl) pyridine, N,N-bis(3-aminopropyl)-2-methoxyethylamine, and N,N-(3-aminopropyl)-2-methoxybenzylamine, respectively, have been synthesised. The crystal structures of five complexes have been determined: [BaL¹][ClO₄]₂ crystallises in the monoclinic space group C2/c(C⁶_2h, no. 15) and has unit-cell dimensions a= 20.310(38), b= 14.453(41), c= 15.137(29)Å, β= 104.84(15)°, and Z= 4; [Ag₂L¹][ClO₄]₂ crystallises in the tetragonal space group I4₁cd(C¹²_4v, no. 110) with a= 28.11 (4), c= 21.618(16)Å, and Z= 16; [Ag₂L²][ClO₄]₂·0.5H₂O crystallises in the triclinic space group P(C¹_i, no. 2) with a= 12.277(16), b= 13.899(14), c= 15.260(50)Å, α= 77.30(20), β= 70.17(20), γ= 71.27(9)°, and Z= 2; [Ag₂L³][ClO₄]₂· 0.5 H₂O crystallises in the triclinic space group P(C¹_i), no. 2) with a= 14.171 (14), b= 18.323(16), c= 12.495(23)Å, α= 99.20(12), β= 120.13(11), γ= 116.35(7)°, and Z= 2; [Ag₂L⁴][ClO₄]₂ crystallises in the monoclinic space group P2₁/a(C⁵_2h, no. 14),a= 16.595(16), b= 13.363(11), c= 23.951 (25)Å, β= 105.43(8)°, and Z= 4. The macrocycles fold to present molecular clefts into which the metals co-ordinate. Modification of the ring size and of the nature of the donor atom in the pendant arm leads to the Ag ⋯ Ag separation in the binuclear silver(I) complexes varying from 2.9 to 6.9 Å.