Layered Ag(I), Cd(II) and Cu(I) Luminescent Coordination Polymers Assembled Through a Tri-Pyridyl Cyclic Triimidazole Ligand

The versatility of a nitrogen rich pyridinic derivative of the cyclic triimidazole scaffold with C3 symmetry is here exploited to obtain three luminescent coordination polymers (CPs). By reaction of 3,7,11-tri(pyridin-4-yl)triimidazo[1,2-a:1′,2′-c:1′′,2′′-e][1,3,5]triazine, (4 py)3TT, with Ag(I), Cd(II) and Cu(I) salts, [Ag{(4-py)3TT}(SO3CF3)]n ⋅ 1/2 nCH2Cl2, [Cd{(4-py)3TT}(NO3)2(EtOH)]n and [(Cu2I2)3{(4-py)3TT}4]n ⋅ xn(H2O,EtOH) are obtained. The trigonal symmetry of (4 py)3TT results in 2D structures with hcb topology in [Ag{(4-py)3TT}(SO3CF3)]n ⋅ 1/2 nCH2Cl2 and [Cd{(4-py)3TT}(NO3)2(EtOH)] and a rare 3,4-connected (3,4-c) topology in [(Cu2I2)3{(4-py)3TT}4]n ⋅ xn(H2O,EtOH). The multifaceted emissive behaviour of the CPs and the free ligand has been investigated and interpreted through spectroscopic, structural and computational studies. The fluorescence and the high energy phosphorescence of [Ag{(4-py)3TT}(SO3CF3)]n ⋅ 1/2 nCH2Cl2, [Cd{(4-py)3TT}(NO3)2(EtOH)]n and (4 py)3TT itself are correlated to singlet and triplet excited states of molecular origin while their low energy phosphorescence derives from supramolecular entities associated with strong π–π interactions with little metal contribution as it is the case for the single phosphorescence observed for [(Cu2I2)3{(4-py)3TT}4]n ⋅ xn(H2O,EtOH). In agreement, unusually long lifetimes in the ms regime are measured for crystals of all compounds.