Transition metal complexes of the PPO/POP ligand: variable coordination chemistry and photo-luminescence properties.

In the current work the tautomeric equilibrium between tetraphenyldiphosphoxane (Ph 2 P-O-PPh 2 , POP) and tetraphenyldiphosphine monoxide (Ph 2 P-P(O)Ph 2 , PPO) in the absence and presence of transition metal precursors is investigated. Whereas with hard transition metal ions, such as Fe(II) and Y(III), PPO-type complexes, such as [FeCl 2 (PPO) 2 ] (1) and [YCl 3 (THF) 2 (PPO)] (2), are formed, softer transition metals ions tend to form so-called coordination stabilised tautomers of the POP ligand form, such as [Cu 2 (MeCN) 3 (μ 2 -POP) 2 ](PF 6 ) 2 (3), [Au 2 Cl 2 (μ 2 -POP)] (4), and [Au 2 (μ 2 -POP) 2 ](OTf) 2 (5). The photo-optical properties of the PPO- and POP-type transition metal complexes are investigated experimentally using photo-luminescence spectroscopy, whereby the presence of metallophillic interactions was found to play a crucial role. The dinuclear copper complex [Cu 2 (MeCN) 3 (μ 2 -POP) 2 ](PF 6 ) 2 (3) shows a very interesting thermochromic behavior and intense photo-luminescence with remarkable phosphoresence lifetimes at 77 K, which can probably be attributed to short intramolecular Cu-Cu distances.