De novo synthesis of hybrid d-f block metal complex salts for electronic charge transport applications.

The advent of d-d type complex salts for designing smart functional materials with versatile utility inspired us to develop a novel type of M(II)-Ce(IV) complex salts [M(II) = Cu and Zn ions]. In this study, we present for the first time a holistic approach to design and prepare metal complex salts of the novel hybrid d-f block type, [Cu(bpy) 2 ] 2 [Ce(NO 3 ) 6 ] 2 (1), [Cu(phen) 2 (NO 3 )] 2 [Ce(NO 3 ) 6 ](HNO 3 ) (2), [Zn(bpy) 2 (NO 3 )][ClO 4 ] (3), and [Zn(phen) 2 (NO 3 )] 2 [Ce(NO 3 ) 6 ] (4); [bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline]. The intrinsic structural and morphological properties of the compounds have been revealed by employing a suite of analytical and spectroscopic methods. X-ray structural analysis reveals that the copper(II) centres in the cationic complex units of 1 and 2 adopt a highly distorted tetrahedral and a rare bicapped square pyramidal coordination geometry, respectively. The zinc(II) ions in both 3 and 4 adopt the rare bicapped square pyramidal geometry while the cerium(IV) ions in 1, 2 and 4 exist in a dodecahedral geometry. Investigation of supramolecular interactions reveals that intermolecular O⋯H and O⋯π short contacts bind the complex units in 1, while predominant π⋯π interactions, along with O⋯H and O⋯π short contacts, produce the binding force among the complex units in 2. We further employed the complex salts (1-4) to construct Schottky devices to reveal the role of these new complex salts in the charge-transport phenomenon. The carrier mobilities ( μ ) for salts 1-4 were determined to be 1.76 × 10 -6 , 9.02 × 10 -6 , 1.86 × 10 -8 , and 4.31 × 10 -8 m 2 V -1 s -1 , with respective transit times ( τ ) of 439, 85, 4.17 × 10 3 , and 1.79 × 10 3 ns, which suggest that complex salt 2 is the best candidate with the highest transport properties among all the complex salts. A crystal engineering perspective sheds light on the charge-transport properties of the complex salts, emphasizing the attribution of the best performance of 2 to its predominant π⋯π interactions. The synthesis of this new type of complex salts, their physicochemical properties and their charge-transport applications envisage great promise for the development of novel crystalline materials with smart functionalities.