Baca Svetlana G, Pope Simon J A, Adams Harry, Ward Michael D
Department of Chemistry, University of Sheffield, Sheffield, U.K.
Inorg Chem. 2008 May 5;47(9):3736-47. doi: 10.1021/ic702353c. Epub 2008 Mar 29.
Slow evaporation of aqueous solutions containing mixtures of Na 2[Os(phen)(CN) 4], Ln(III) salts (Ln = Pr, Nd, Gd, Er, Yb), and (in some cases) an additional ligand such as 1,10-phenanthroline (phen) or 2,2'-bipyrimidine (bpym) afforded crystalline coordination networks in which the [Os(phen)(CN) 4] (2-) anions are coordinated to Ln(III) cations via Os-CN-Ln cyanide bridges. The additional diimine ligands, if present, also coordinate to the Ln(III) centers. Several types of structure have been identified by X-ray crystallographic studies. Photophysical studies showed that the characteristic emission of the [Os(phen)(CN) 4] (2-) chromophore, which occurs at approximately 680 nm in this type of coordination environment with a triplet metal-to-ligand charge transfer ( (3)MLCT) energy content of approximately 16 000 cm (-1), is quenched by energy transfer to those Ln(III) centers (Pr, Nd, Er, Yb) that have low-lying f-f states capable of accepting energy from the Os(II)-based (3)MLCT state. Time-resolved studies on the residual (partially quenched) Os(II)-based luminescence allowed the rates of Os(II) --> Ln(III) energy transfer to be evaluated. The measured rates varied substantially, having values of >5 x 10 (8), approximately 1 x 10 (8), and 2.5 x 10 (7) s (-1) for Ln = Nd, Er or Yb, and Pr, respectively. These differing rates of Os(II) --> Ln(III) energy transfer can be rationalized on the basis of the availability of f-f states of the different Ln(III) centers that are capable of acting as energy acceptors. In general, the rates of Os(II) --> Ln(III) energy transfer are an order of magnitude faster than the rates of Ru(II) --> Ln(III) energy transfer in a previously described series of [Ru(bipy)(CN) 4] (2-)/Ln(III) networks. This is ascribed principally to the lower energy of the Os(II)-based (3)MLCT state, which provides better spectroscopic overlap with the low-lying f-f states of the Ln(III) ions.
含有Na₂[Os(phen)(CN)₄]、Ln(III)盐（Ln = Pr、Nd、Gd、Er、Yb）以及（某些情况下）额外配体如1,10 - 菲咯啉（phen）或2,2'-联嘧啶（bpym）的水溶液缓慢蒸发，得到晶体配位网络，其中Os(phen)(CN)₄阴离子通过Os - CN - Ln氰基桥与Ln(III)阳离子配位。若存在额外的二亚胺配体，它们也会与Ln(III)中心配位。通过X射线晶体学研究确定了几种结构类型。光物理研究表明，在这种配位环境中，Os(phen)(CN)₄发色团的特征发射出现在约680 nm处，其三重态金属到配体电荷转移（(³)MLCT）能量约为16000 cm⁻¹，该发射通过能量转移到那些具有能接受来自基于Os(II)的(³)MLCT态能量的低能级f - f态的Ln(III)中心（Pr、Nd、Er、Yb）而被淬灭。对残余的（部分淬灭的）基于Os(II)的发光进行时间分辨研究，从而评估Os(II)→Ln(III)的能量转移速率。测得的速率变化很大，对于Ln = Nd、Er或Yb以及Pr，其值分别为>5×10⁸、约1×10⁸和2.5×10⁷ s⁻¹。基于不同Ln(III)中心作为能量受体的f - f态的可用性，可以解释这些不同的Os(II)→Ln(III)能量转移速率。一般来说，在先前描述的一系列Ru(bipy)(CN)₄/Ln(III)网络中，Os(II)→Ln(III)的能量转移速率比Ru(II)→Ln(III)的能量转移速率快一个数量级。这主要归因于基于Os(II)的(³)MLCT态的能量较低，它与Ln(III)离子的低能级f - f态具有更好的光谱重叠。
