Synthesis, crystal structures, and dual donor luminescence sensitization in novel terbium tetracyanoplatinates

A series of novel terbium tetracyanoplatinate compounds all incorporating tridentate 2,2':6'2″-terpyridine (terpy) or 4'-chloro-2,2':6'2″-terpyridine (terpy-Cl) were synthesized and used to investigate the phenomenon of dual-donor sensitization of Tb(3+). Judicious choice of the Tb(3+) salt and reaction conditions results in the isolation of {Tb(terpy)(H2O)2(NO3)Pt(CN)4}·CH3CN (1A), {Tb(terpy)(H2O)2(NO3)Pt(CN)4}·3.5H2O (1B), {Tb(terpy-Cl)(H2O)2(NO3)Pt(CN)4}·2.5H2O (2), [Tb(terpy)(H2O)2(CH3COO)2]2Pt(CN)4·4H2O (3), or [Tb2(terpy)2(H2O)2(CH3COO)5]2Pt(CN)4·7H2O (4). The compounds 1A, 1B, and 2 contain one-dimensional polymeric structures with bridging of [Tb(L)(NO3)(H2O)2](2+) (L = terpy or terpy-Cl) moieties by cis-bridging tetracyanoplatinate (TCP) anions as determined via single-crystal X-ray diffraction studies. Both 3 and 4, however, contain Tb(3+) coordinated by multiple acetate ligands and terpy, but not TCP, and are classified as zero-dimensional complex salts. Platinophilic interactions that dominate tetracyanoplatinate structural chemistry are present in the form of dimeric units in the polymeric compounds, but are totally absent in 3 and 4. The structural differences result in markedly different luminescence properties for the two classes of compounds. All of the polymeric compounds display efficient donor-acceptor intramolecular energy transfer (IET) from the terpy unit to the Tb(3+) ion. Although the TCP units are also directly coordinated to the Tb(3+) ion in the three polymers, only in 1B and 2 are the Pt···Pt interactions strong enough to provide MMLCT bands of appropriate energy to result in a dual-donor effect to the Tb(3+) sensitization. Even in these cases, TCP does not efficiently sensitize the Tb(3+), rather a broad band TCP emission results. However, terpy and acetate ligands are bonded directly to the Tb(3+) ion in 3 and 4 and provide a strong dual-donor sensitization effect as evidenced by the large QY for Tb(3+).