Compartmental ligands. Part 4. The crystal and molecular structures of some oxovanadium(IV) complexes of acyclic ligands derived from heptane-2,4,6-trione and α,ω-alkanediamines

Abstract

Mononuclear oxovanadium(IV) complexes of acyclic Schiff bases derived from heptane-2,4,6-trione and α,ω-alkanediamines have been synthesised from the corresponding macrocyclic precursors. Three-dimensional X-ray crystal-structure analyses have been carried out on [6,12-dimethyl-7,11-diazaheptadeca-5,12-diene-2,4,14,16-tetraonato(2–)-O²O⁴O¹⁴O¹⁶]oxovanadium(IV)–chloroform (1/1), (4b; M = VO)·CHCl₃, and two forms of [6,11-dimethyl-7,10-diazahexadeca-5,11-diene-2,4,13,15-tetraonato(2–)-O²O⁴O¹³O¹⁵]oxovanadium(IV), (4a; M = VO). The last two forms gave evidence for co-crystallisation of the corresponding homobinuclear bis(oxovanadium) complex. Complex (4b; M = VO)·CHCl₃, has Z= 2 in a triclinic cell with space group P, and dimensions a= 10.966(5), b= 8.358(4), c= 15.226(8)Å, α= 92.36(8), β= 123.77(11), and γ= 102.16(10)°; R= 0.0385 for 2 985 reflections. Complex (4a; M = VO) has Z= 4 in a monoclinic unit cell with space group P2₁/n and dimensions a= 9.230(3), b= 23.657(15), c= 8.177(6)Å, and β= 102.160(14)°(R= 0.0638 for 987 reflections), and has Z= 2 in a triclinic cell with space group P and dimensions a= 8.459(6), b= 12.002(9), c= 8.789(7)Å, α= 80.140(7), β= 101.447(12), and γ= 93.946(7)°(R= 0.0545 for 1 598 reflections). The X-ray structure of the heterobinuclear complex [6,11-dimethyl-7,10-diazahexadeca-5,11-diene-2,4,13,15-tetraonato(4–)-N⁷N¹⁰O⁴O¹³; O²O⁴O¹³O¹⁵]copper(II)oxovanadium(IV), (5a; M¹= Cu, M²= VO), is also reported and has Z= 4 in a monoclinic cell with space group P2₁/c and dimensions a= 8.325(20), b= 12.117(11), c= 18.105(18)Å, and β= 108.93(6)°; R= 0.0613 for 2 480 reflections. The crystal structures confirm the compartmental occupancies for the complexes and show that the Cu–V distance in (5a; M¹= Cu, M²= VO) is 2.985 Å. A proposal is made for the mode of incorporation of the second oxovanadium into the mononuclear complex.