A Rare Structural Motif for a Luminescent Cu(I) Coordination Polymer with 3-(Pyridin-2-yl)triimidazotriazine

Abstract

The coordination ability of the pyridine derivative of cyclic triimidazole, namely 3-(pyridin-2-yl)triimidazotriazine (TT-Py) towards Cu(I) was explored. TT-Py is an appealing nitrogen-rich ligand characterized by the presence of three imidazole nitrogen atoms with trigonal symmetry and a pyridine moiety, available for coordination to metal ions. The multidentate nature of TT-Py allows to isolate, by reaction with CuI at room temperature, the one-dimensional coordination network [Cu2I2(TT-Py)]n (1). 1 is characterized by a rare structural network built-up by the combination in a 1:2 ratio of two common motifs for Cu(I) halides coordination polymers, which are the double-stranded stair and the zig-zag chain. 1 displays one broad long-lived emission in the solid state, which has been associated, by the support of DFT and TDDFT calculation, with low-energy transitions of MLCT or XMLCT character.

2-Pyridine cyclic triimidazole as a chelating and bridging ligand in mono- and hexa-nuclear Re(i) complexes with emissive properties in solution and in the solid state

“…18 In particular, to allow the ligand to chelate, the pyridyl substituent must rotate around the TT-Py bond (as evidenced by the N7–C13–C5–N2 dihedral angle of 46.8°, to be compared to values in the range of 144.4–156.1° found in the different polymorphs of the free ligand) and tilt to accommodate the rhenium atom (as evidenced by the N7–C13–C5 bond angle of 123.45°, ten degrees larger than the values in the range of 112.46–113.71° found for the free ligand). A similar conformation was adopted by TT-Py in previously reported species, in which it similarly acts as a chelating ligand, namely [Cu 2 I 2 ( TT-Py )] n 4 and [Cu(μ-NO 3 )(NO 3 )( TT-Py )] n . 2 e Hexanuclear species 2 (as found in 2 ·4( n -hexane) crystal) contains two [ReCl(CO) 3 ( TT-Py )] moieties whose geometry is quite similar to that observed in mononuclear complex 1 (see Table S3, ESI†).…”

“…From the molecular point of view, 2 can also be considered as a dimeric structure in which two mononuclear 1 units act as bridging ligands towards two “Re 2 (μ-Cl) 2 (CO) 6 ” fragments. The coordination features of TT-Py in 2 resemble those observed in a related Cu( i ) coordination polymer 4 where the ligand acts as a bridging-chelating fragment through the pyridine and imidazole nitrogen atoms.…”

“…From the crystal structures obtained so far using TT-Py as the ligand towards Cu( ii ), Re( i ) and Cu( i ), it is evident that the versatility of this simple molecule means it is able to adopt different coordination modes to give mononuclear, polynuclear and extended 1D structures. In particular, in paddle-wheel dinuclear [Cu 2 (CH 3 COO) 4 ( TT-Py ) 2 ], TT-Py behaved as monodentate through one imidazole nitrogen; 2 e in [Cu(μ-NO 3 )(NO 3 ) ( TT-Py )], it acted as a chelating ligand, 4 and in the coordination polymer [Cu 2 I 2 ( TT-Py )] n , it was found to bridge through the seven-membered chelating ring and one of the three nitrogen atoms of triimidazole. Therefore, additional interesting structural motifs are expected by investigating the coordination ability of this ligand with other metals.…”

“…Previous results indicated the versatility of TT-Py, able to behave towards Cu(II) and Cu(I) both as a chelating ligand 2e and as a bridging ligand through the seven-membered chelating ring and one of the three nitrogen atoms of triimidazole. 4 We therefore investigated the same versatility towards Re(I) by using different metal : ligand stoichiometric ratios. In particular, 1 was isolated in 460% yield when TT-Py was reacted with one equivalent of [ReCl(CO) 5 ] (see eqn ( 1) and Scheme 1).…”

“…In particular, 3-(pyridin-2-yl)triimidazo [1,2-a:1 0 ,2 0 -c:1 00 ,2 00 -e] [1,3,5]triazine, TT-Py (Chart 1), revealed excitation dependent multicomponent emissive behaviour 3 and varied (mono-dentate, chelating-bidentate and m-bridging chelating) coordination modes towards Cu(II) 2e and Cu(I). 4 In fact, TT-Py, due to the presence of two nitrogen atoms, namely that on the pyridine ring (N6 0 in Chart 1) and the other on the imidazolic unit (N5) at an appropriate distance, is able to act as a chelating ligand. Moreover, additional nitrogen atoms of the triimidazole moiety are available to obtain molecular or extended coordination structures.…”