Expanding the Coordination Chemistry of Decavanadate through π-Hole Interactions with Transition-Metal Cyclen Complexes: Electronic Features and Dye Adsorption

High Resolution Image Download MS PowerPoint Slide The hybrid decavanadate with macrocycle cyclen (1,4,7,10-tetraazacyclododecane) complexes with the formula [Ni(cyclen)(H 2 O) 2 ] 2 [H 2 V 10 O 28 ]·2H 2 O ( 1 ) was prepared as an ionic pair, while [{Cu(cyclen)} 2 (H 2 V 10 O 28 )]·9H 2 O ( 2 ) and [{Zn(cyclen)} 3 (V 10 O 28 )]·4H 2 O ( 3 ) were obtained as discrete molecular entities. The structures of 2 and 3 revealed a new coordination mode for the decavanadate anion, involving a triply bridging oxygen (−μ 3 -O B ) and {TM(cyclen)} 2+, where TM = Cu(II) or Zn(II). Electrostatic Surface Potential analysis showed pronounced π-holes in the {Cu(cyclen)} 2+ and {Zn(cyclen)} 2+ fragments, whereas {Ni(cyclen)} 2+ lacks this feature due to stronger metal-cyclen σ-bonding. The Independent Gradient Model based on Hirshfeld partition analysis of {TM(cyclen)}/decavanadate interfaces demonstrated that intramolecular noncovalent interactions play a key role in structural stability. The low Intrinsic Bond Strength Index for the Cu–O B bond (0.087) suggests a weak, semicoordinative interaction with approximately half the strength of the Zn–O B coordination bond (0.169). The adsorption of methylene blue was characterized as a surface phenomenon. The bleaching efficiency, 2 > 1 > 3, was determined by the distribution of their asymmetric surface charge and particle size. These hybrid compounds provide a valuable model for understanding and advancing decavanadate coordination chemistry and for the application of polyoxometalates to remove prevalent contaminants from wastewater.