Synthesis, crystal structure and spectroscopic properties of a new type of pentanuclear zinc(II) complex

Abstract The article describes synthesis, crystal structure, ESI-MS and steady state and time-resolved fluorescence spectrum of a pentanuclear zinc(II) compound of composition [Zn II 5 (HL) 2 (μ 3 -OH) 2 (NO 3 ) 4 ] ( 1 ), where H 3 L is the [1 + 2] condensation product of 4-ethyl-2,6-diformylphenol and 2-amino-2-methyl-1-propanol. The phenol moiety and one of the two alcohol moieties of a H 3 L get deprotonated and therefore two ONO compartments of [HL] 2− in 1 are inequivalent (O(alkoxide)N(imine)O(phenoxide) and O(alcohol)N(imine)O(phenoxide)). Each of the two compartments of each [HL] 2− in 1 is occupied by a Zn II ion, to form a Zn II 2 fragment. Two such fragments are linked by two μ 3 -hydroxide ligands to form a dimer-of-dinuclear type Zn II 4 fragment. Each of the two alkoxide oxygen atoms bridges one Zn II in the Zn II 4 fragment and a fifth Zn II ion (dangling metal ion) to form the pentanuclear system. The structure reveals that it is a new type of pentanuclear system among the related compounds. Notably, the pentanuclear moiety is retained in solution as evidenced from conductance measurement. The title compound exhibits fluorescence behaviour with the emission band at 447 nm on excitation at 384 nm. The quantum yield is 0.05. TCSPC reveals a monoexponential decay in 1 . ESI-MS of 1 reveal the appearance of signals of positive ions corresponding to Zn II 5 , Zn II 2 and Zn II metallic systems as well as to H 3 L ligand system.