TechScape: The Science, Technology and Education Journal of IIT Jodhpur
Volume 01, Issue 03, August 2021

Main Group Metal Complexes as Molecular Materials

Abhishek Mishra and Ramesh K. Metre

Nanomaterials have overpowered the electronic and advanced material industry in past few decades because of their uncountable properties originating from the smaller size and low band gap.¹ More recently, coordination complexes of transition and lanthanide metal ions were explored as molecular materials in electronic devices.^2,3 These organometallic molecular complexes are considered as potential candidates for electronic and electrical devices in recent time due to their discrete size, controllable design, and ease of handling. Literature shows numerous example of organometallic complexes successfully used as molecular materials in various devices such as OLEDs (organic light emitting devices)⁴, molecular switches⁵, molecular wires⁶, memristive devices⁷, dye sensitized solar cells⁸, etc.

However, intriguing research is still underway for developing new strategies and molecular architectures for these advanced functional molecular materials. Organometallic complexes of main group metals have, with their recently reported properties, been considered as promising molecular materials. Main group organometallic complexes have proven their suitability for being molecular materials in terms of their solution processable synthesis, versatile design, solubility, flexibility, stability, and ease of processing etc. Recent literature reports on “the rearrangement of NHC to abnormal NHC by an organotin sulphide cation⁹, a photon up-conversion of IR light into a broad white light spectrum using [(R^delocSn)₄S₆] (R^deloc = 4–(CH₂=CH)–C₆H₄)¹⁰, an interesting Zn metal trapping phenomenon by functionalizing the organotin sulfide cage¹¹, and a molecular precursor based on Zn/Sn/S ternary complex for CZTS (Cu₂ZnSnS₄) i.e., a potential material for thin film solar cells¹²”, provides further evidence of their wide range of interesting properties.

Recently, we have reported a tetranuclear monoorganotin sulfide cage [(RSn^IV)₄(μ-S)₆]·2CHCl₃·4H₂O (1) (R = 2-phenylazophenyl) exploiting the intramolecular N→Sn coordination. The complex 1 is further explored as active material for the fabrication of solution-processable resistive memory switching device. The current-voltage (I-V) characteristics of the device showed an excellent memory behaviour with low write voltage i.e., -1.4 V. The device also displayed a good ON/OFF ratio of 10³ with retention time of 10000s. The complex 1 is the first organotin complex to exhibit the memristive behaviour.¹³ On the other hand, we reported another hydroxido-bridged dinuclear monoorganostannoxane [(RSn^IV)₂(μ-OH)(μ-OMe)Cl₄]·CH₃OH (R = 2-phenylazophenyl) (2) which was explored as active material for NDR (negative differential resistance) device. The I−V characteristic studies performed on the device made using 2 found to exhibit excellent NDR behavior in the region of 1.5−2.5 V.¹⁴