Synthetic strategy, magnetic and spectroscopic properties of the terpyridine complexes [Cu(terpy)X(H2O)n]Y (X = NCO, NCS or N3; n= 0 or 1; Y = NO3 or PF6). Crystal structures of the azidenitrate and azidehexafluoro-phosphate

Abstract

Eight copper(II) complexes with 2,2′:6′,2″-terpyridine (terpy) and pseudohalide ligands. [Cu(terpy)X-(H₂O)_n]Y [X = NCO, NCS or N₃; n= 0 or 1; Y = NO₃ or PF₆] have been prepared by following a described synthetic strategy. The crystal structures [Cu(terpy)(N₃)(H₂O)]_x[NO₃]_x and [Cu(terpy)(N₃)-(H₂O)]₂[PF₆]₂ have been determined: monoclinic, space group P2₁/n, a= 8.849(2), b= 10.343(1), c= 18.168(3)Å, β= 97.71(2)°, Z= 4; triclinic, space group P, a= 9.0609(6), b= 10.2798(8), c= 11.309(1)Å, α= 105.22(7), β= 86.58(7), γ= 112.90(6)°, Z = 2. In both complexes [Cu(terpy)(N₃)-(H₂O)]⁺ entities are present. For the first compound these form a chain structure, via hydrogen bonding between the co-ordinated water molecule and the nitrate ion. However, the structure of the second compound is built from dimeric [Cu₂(terpy)₂(N₃)₂(H₂O)₂]²⁺ cations in which the copper ions are connected by one-end bridging azide groups and PF₆^– counter ions. The co-ordination geometry of the copper(II) ion is square pyramidal and octahedral for the two compounds respectively. The complexes studied can be grouped into three structural types, within each of which the compounds are isostructural. The anhydrous and hydrated hexafluorophosphates have dimeric structures; however, the nitrate compounds are associated in chains. Magnetic susceptibility measurements revealed weak magnetic interactions for all of them. The EPR spectra show ‘half-field’ forbidden transitions for all the complexes and even singlet-to-triplet forbidden transitions for the nitrates. From the positions of these last signals the exchange parameters for the nitrate compounds have been determined. The magnetic interactions have been analysed taking into account several exchange pathways.