Solid-state photoluminescence sensitization of Tb3+ by novel Au2Pt2 and Au2Pt4 cyanide clusters.

The syntheses are reported for two novel Tb(3+) heterotrimetallic cyanometallates, K(2)[Tb(H(2)O)(4)(Pt(CN)(4))(2)]Au(CN)(2)·2H(2)O (1) and [Tb(C(10)N(2)H(8))(H(2)O)(4)(Pt(CN)(4))(Au(CN)(2))]·1.5C(10)N(2)H(8)·2H(2)O (2) (C(10)N(2)H(8) = 2,2'-bipyridine). Both compounds have been isolated 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, tetragonal, space group P4(2)/nnm, a = 11.9706(2) Å, c = 17.8224(3) Å, V = 2553.85(7) Å(3), Z = 4; 2, triclinic, space group P1, a = 10.0646(2) Å, b = 10.7649(2) Å, c = 17.6655(3) Å, α = 101.410(2)°, ß = 92.067(2)°, γ = 91.196(2)°, V = 1874.14(6) Å(3), Z = 2. For the case of 1, the structure contains Au(2)Pt(4) hexameric noble metal clusters, while 2 includes Au(2)Pt(2) tetrameric clusters. The clusters are alike in that they contain Au-Au and Au-Pt, but not Pt-Pt, metallophilic interactions. Also, the discrete clusters are directly coordinated to Tb(3+) and sensitize its emission in both solid-state compounds, 1 and 2. The Photoluminescence (PL) spectra of 1 show broad excitation bands corresponding to donor groups when monitored at the Tb(3+) ion f-f transitions, which is typical of donor/acceptor energy transfer (ET) behavior in the system. The compound also displays a broad emission band at ∼445 nm, assignable to a donor metal centered (MC) emission of the Au(2)Pt(4) clusters. The PL properties of 2 show a similar Tb(3+) emission in the visible region and a lack of donor-based emission at room temperature; however, at 77 K a weak, broad emission occurs at 400 nm, indicative of uncoordinated 2,2'-bipyridine, along with strong Tb(3+) transitions. The absolute quantum yield (QY) for the Tb(3+) emission ((5)D(4) → (7)F(J (J = 6-3))) in 1 is 16.3% with a lifetime of 616 µs when excited at 325 nm. In contrast the weak MC emission at 445 nm has a quantum yield of 0.9% with a significantly shorter lifetime of 0.61 µs. For 2 the QY value decreases to 9.3% with a slightly shorter lifetime of 562 µs. The reduced QY in 2 is considered to be a consequence of (1) the slightly increased donor-acceptor excited energy gap relative to the optimal gap suggested for Tb(3+) and (2) Tb(3+) emission quenching via a bpy ligand-to-metal charge transfer (LMCT) excited state.

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''-terpyridine (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(15)H(11)N(3))(H(2)O)(2)(NO(3))(Pt(CN)(4)) x CH(3)CN (1), {Eu(C(15)H(11)N(3))(H(2)O)(3)}(2)(Pt(CN)(4))(3) x 2 H(2)O (2), or [Eu(C(15)H(11)N(3))(H(2)O)(2)(CH(3)COO)(2)](2)Pt(CN)(4) x 3 H(2)O (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 (MoK alpha, lambda = 0.71073 A, T = 290 K): 1, monoclinic, space group P2(1)/c, a = 12.835(1), b = 15.239(1), c = 13.751(2) A, beta = 105.594(9) degrees, V = 2590.8(5) A(3), Z = 4; 2, triclinic, space group P1, a = 9.1802(8) A, b = 10.8008(9) A, c = 13.5437(9) A, alpha = 84.491(6) degrees, beta = 75.063(7) degrees, gamma = 79.055(7) degrees, V = 1272.4(2) A(3), Z = 1; 3, triclinic, space group P1, a = 12.110(3) A, b = 12.7273(11) A, c = 18.7054(16) A, alpha = 92.859(7) degrees, beta = 92.200(11) degrees, gamma = 118.057(10) degrees, V = 2534.8(7) A(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 lanthanide emission.