Monomer, dimer or cyclic helicate? Coordination diversity with hard-soft P,N-donor ligands

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 [Cu-2(1)(2)][PF6](2)center dot 6CH(2)Cl(2); 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 [Cu-2(3)(2)][PF6](2), each bridging ligand in the centrosymmetric [Cu-2(3)(2)](2+) ion acts as a P,Nchelate 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 Lambda Lambda Lambda Lambda Lambda Lambda- and Lambda Lambda Lambda Lambda Lambda Lambda-enantiomers are present in the crystal lattice; in [Cu-6(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.