Discrete and Polymeric Cobalt Pyrophosphates Derived from Pyrophosphoric Acid Diester Ar 2 H 2 P 2 O 7

• Published in: European journal of inorganic chemistry 2020-06, Vol.2020 (24), p.2352-2361
• Main Authors: Sharma, Kamna, Gupta, Sandeep K., Murugavel, Ramaswamy
• Format: Article
• Language: English
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.202000484

While the structural elucidation and coordination chemistry of organo‐monophosphates have been well investigated, research on the simplest member of organo‐oligophosphates, viz. diorganopyrophosphates, is relatively rare due to the inherent hydrolytic instability of the ligand. Water elimination from the 2,6‐diisopropyl phenyl phosphate (dippH 2 ) by the action of dicyclohexylcarbodiimide (DCC) results in the isolation of a diorganopyrophosphates ligand formulated as [O{P(OAr)(OH)(O)} 2 ] ( 1 or pyrodippH 2 ) (Ar = 2,6‐diisopropylphenyl). Due to the instability of 1 , it has been transformed into its sodium salt [O{P(OAr)(ONa)(O)} 2 ] ( 2 ), which has been used for further reactions to prepare cobalt pyrophosphate complexes 3 – 7 . Reaction of 2 with anhydrous cobalt(II) chloride in the presence of N‐heterocyclic ligands results in the formation of [Co(pyrodipp)(imz) 3 ] ( 3 ), [Co(pyrodipp)(bpy) 2 ](CH 3 OH) ( 4 ) and [Co(pyrodipp)(phen) 2 ] ( 5 ) (imz = imidazole; bpy = 2,2'‐bipyridine; phen = 1,10‐phenanthroline). Use of multidentate ancillary ligand such as 4‐pyridyl‐2,2':6',2''‐terpyridine (pyterpy) under similar reaction conditions leads to the formation of a one‐dimensional zig‐zag cobalt pyrophosphate coordination polymer [Co(pyrodipp)(pyterpy)(CH 3 OH)] n ( 6 ). In the absence of any ancillary ligand, the reaction between cobalt(II) chloride and 2 in acetonitrile results in the isolation of an interesting inorganic polymer [Co(pyrodipp)(CH 3 CN) 2 ] n ( 7 ), whose backbone consists of a chain of spirocycles of CoP 2 O 3 rings, joined at the cobalt centers. The newly synthesized cobalt pyrophosphates 3 – 7 have been characterized by both analytical and spectroscopic techniques, magnetic studies apart from single‐crystal X‐ray diffraction studies in each case. A striking and persistent structural feature in 3 – 7 is the presence of the cobalt pyrophosphate six‐membered metallacycle Co(OPOPO). While cobalt metal exists in trigonal bipyramidal geometry in complex 3 , distorted octahedral coordination geometry is observed for cobalt centers in complexes 4 – 7 .