Emission enhancement through dual donor sensitization: Modulation of structural and spectroscopic properties in a series of europium tetracyanoplatinates

The synthesis of three different europium tetracyanoplatinates all incorporating 2,2′:6′,2″-terpyrldine (terpy) have been carried out in acetonitrile/water mixtures by reaction of Eu 3+ salts with terpy and potassium tetracyanoplatinate. The use of different Eu 3+ sources results In the isolation of Eu(C 15H 11N 3)(H 2O) 2(NO 3)(Pt(CN) 4).CH 3CN (1), {Eu(C 15H 11N 3)(H 2O) 3} 2(Pt(CN) 4) 3. 2H 2O (2), or [Eu(C 15H 11N 3)(H 2O) 2(CH 3COO) 2] 2Pt(CN) 4.3H 2O (3) for the nitrate, triflate, or acetate salts, respectively. All three compounds have been prepared as colorless crystals, and single-crystal X-ray diffraction has been used to investigate their structural features. Crystallographic data (MoKα,λ =0.71073 Å, T= 290 K): 1, monoclinic, space group P2 1/c, a = 12.835 (1), b = 15.239(1), c = 13.751 (2) Å,β = 105.594(9)°, V= 2590.8(5) Å 3, Z= 4; 2, triclinic, space group P1̄, a = 9.1802(8) Å,b= 10.800819) Å, c= 13.5437(9) Å, α = 84.491(6)°, β = 75.063(7)° γ = 79.055(7)°, V= 1272.4(2) Å 3, Z= 1 ; 3, triclinic, space group P1,̄ a = 12.110(3) Å, b= 12.7273(11) Å, c= 18.7054(16) Å, α = 92.859(7)°, β = 92.200(11)°, γ = 118.057(10)°, V= 2534.8(7) Å 3, Z= 2. Variation of the counteranions in these systems provides the opportunity to modify the structures and coordination environment of Eu 3+ for 1-3. Compounds 1 and 2 are both one-dimensional, polymeric compounds that contain Eu 3+ ions chelated by terpy and bridged by tetracyanoplatinate anions. 3 is a zero-dimensional complex salt in which Eu 3+ is coordinated by terpy, acetate, and water, but not tetracyanoplatinate. The structural differences result In varying sensitization phenomena for the three compounds. Compounds 1 and 2 display efficient donor-acceptor intramolecular energy transfer (IET) where dual donor species, terpyridine and tetracyanoplatinate, simultaneously enhance the acceptor Eu 3+ emission. In both compounds the donor species are directly coordinated to the acceptor ion, and hence a highly efficient dual-donor effect is exhibited for the IET mechanisms. In 3 where only the terpy ligand Is directly coordinated to Eu 3-, the sensitization involves only one donor species. The Pt(CN) 4 2- unit In 3, which lacks direct bonding to Eu 3-, exhibits strong emission indicating the lack of cooperative enhancement of the lanthanlde emission. © 2009 American Chemical Society.