RESUMO
The complex [Cr(tpy)(O3SCF3)3] (tpy = 2,2':6',2''-terpyridine) is readily made from [Cr(tpy)Cl3] and is a convenient precursor to [Cr(tpy)2][PF6]3 and to [Cr(tpy)(4'-(4-tolyl)tpy)][PF6]3 and [Cr(tpy)(5,5''-Me2tpy)][PF6]3 (4'-(4-tolyl)tpy = 4'-(4-tolyl)-2,2':6',2''-terpyridine; 5,5''-Me2tpy = 5,5''-dimethyl-2,2':6',2''-terpyridine); these are the first examples of heteroleptic bis(tpy) chromium(III) complexes. The single crystal structures of 2{[Cr(tpy)2][PF6]3}·5MeCN, [Cr(tpy)(4'-(4-tolyl)tpy)][PF6]3·3MeCN and [Cr(tpy)(5,5''-Me2tpy)][PF6]3·3MeCN have been determined. Each cation contains the expected octahedral {Cr(tpy)2}(3+) unit; in all three structures, the need to accommodate three anions per cation and the solvent molecules prevents the formation of a grid-like array of cations that is typical of many lattices containing {M(tpy)2}(2+) motifs. Three reversible electrochemical processes are observed for [Cr(tpy)(4'-(4-tolyl)tpy)][PF6]3 and [Cr(tpy)(5,5''-Me2tpy)][PF6]3, consistent with those documented for [Cr(tpy)2](3+). At pH 6.36, aqueous solutions of [Cr(tpy)2][PF6]3 are stable for at least two months. However, contrary to the expectations of the d(3) Cr(3+) ion being a kinetically inert metal centre, the tpy ligands in [Cr(tpy)2](3+) are labile in the presence of base; absorption and (1)H NMR spectroscopies have been used to monitor the effects of adding NaOH to aqueous and CD3OD solutions, respectively, of the homo- and heteroleptic complexes. Ligand dissociation is also observed when [Bu4N]F is added to CD3OD solutions of the complexes, but in aqueous solution, [Cr(tpy)2][PF6]3 is stable in the presence of fluoride ion.
RESUMO
We report the synthesis of copper(I) complexes of three ligands which contain a potential P,N,N,P-metal binding site. Elemental analysis confirms that the bulk products possess a composition of [CuL][PF6] where L = 1, 2 or 3. Electrospray mass spectrometry (ESI MS) provides evidence for speciation in MeCN or MeOH solutions and the formation of both [CuL]+ and [Cu2L2]2+; addition of NaCl to the ESI MS samples aids the observation of dinuclear species as [Cu2L2Cl]+ ions. NMR spectroscopic data for a CD3CN solution of [Cu(1)][PF6] were consistent with a mononuclear species, but more complex multinuclear spectra were observed for the same compound dissolved in CD2Cl2. In the solid state, dimeric species dominate. Crystals grown from CH2Cl2 solutions of [Cu(1)][PF6] are found to be [Cu2(1)2][PF6]2·6CH2Cl2; each Cu+ ion in the centrosymmetric cation is bound in an N,O,P,P-coordination sphere, the N-donor originating from the pyridine ring. In [Cu2(3)2][PF6]2, each bridging ligand in the centrosymmetric [Cu2(3)2]2+ ion acts as a P,N-chelate to each Cu+ ion. Competing with this dimeric assembly is that of a circular helicate in which each ligand 3 bridges adjacent pairs of copper(I) ions in a chiral, hexameric complex; both the Δ,Δ,Δ,Δ,Δ,Δ- and Λ,Λ,Λ,Λ,Λ,Λ-enantiomers are present in the crystal lattice; in [Cu6(3)6]6+, each ligand coordinates as a bis(P,N-chelate). The solution absorption spectra of [Cu(1)][PF6], [Cu(2)][PF6] and [Cu(3)][PF6] are dominated by ligand-based transitions and none of the copper(I) complexes exhibits emissive behaviour in solution.
