Reactions of bis-(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)copper(II) with pyrazine and the crystal structures of the 1:1 and 2:l complexes

Abstract

Reaction of Cu(hfac)₂,H₂O [hfac =(CF₃CO)₂·CH] with equimolar amounts of pyrazine (pyz) in carbon tetrachloride gave the 1 : 1 complex (I) Cu(hfac)₂(pyz). Recrystallisation from hot carbon tetrachloride gave (I) together with (II)[Cu(hfac)₂]₂(pyz). A 1 : 2 mixture of reactants gave Cu(hfac)₂(pyz)₂.

Three-dimensional crystal structure analyses were carried out on (I) and (II). The structures were solved from diffractometer data by the heavy-atom method and refined by least squares to R 0·58 [(I), 742 reflections] and 0·081 [(II), 956 reflections]. (I) is a linear co-ordination polymer, with Z= 1 in a triclinic unit cell with a= 11·228(6), b= 6·821(4), c= 6·742(7)Å, α= 109° 06′(5′), β= 103° 27′(3′), γ= 95° 12′(2′), space group P. The copper is six-co-ordinated and occupies a crystallographic centre of symmetry; the two chelating hfac rings give Cu–O 1·924 and 2·004(7) and the pyrazine rings give Cu–N 2·529(9)Å. Each pyrazine ring bridges two copper atoms related by the translation [0,1,1].

The 2: 1 complex (II), is monoclinic, with Z= 2 in a unit cell with a= 10·750(5), b= 6·761(10), c= 23·732(12)Å, β= 93° 04′(1′), space group P2₁/c. The centre of the pyrazine ring is on a crystallographic centre of symmetry and the five-co-ordinated copper atoms are not required to have any symmetry; in fact the co-ordination is square pyramidal, with mean base Cu–O bonds 1·94(1)Å. The copper atom is displaced 0·241 Å from the basal plane towards the nitrogen atom, Cu–N 2·250(17)Å.

In both complexes the bond lengths within the ligands are in the usual ranges.