Role of 4,4′-bipyridine versus longer spacers 4,4′-azobipyridine, 1,2-bis(4-pyridyl)ethylene, and 1,2-bis(pyridin-3-ylmethylene)hydrazine in the formation of thermally labile metallophosphate coordination polymers

• Published in: Inorganic chemistry frontiers Vol. 2; no. 1; pp. 55 - 66
• Main Authors: Rajakannu, Palanisamy, Howlader, Rana, Kalita, Alok Ch, Butcher, Raymond J., Murugavel, Ramaswamy
• Format: Journal Article
• Language: English
• Published: 2015
• ISSN: 2052-1553; 2052-1553
• DOI: 10.1039/C4QI00149D

One dimensional metallophosphate coordination polymers {[M(dtbp) 2 (azopy)(H 2 O) 2 ]·(azopy)} x (M = Mn ( 1 ); Co ( 2 ); Cu ( 3 ); Cd ( 4 )) have been synthesized from the reaction of a suitable metal precursor with di- tert -butylphosphate (dtbp-H) in the presence of ditopic linker 4,4′-azobipyridine (azopy) in a 1 : 2 : 2 stoichiometric ratio. Isostructural compounds 1–4 have been characterized by analytical and spectroscopic methods and single crystal X-ray diffraction studies. Single crystal X-ray diffraction measurements further reveal that compounds 1–3 (all C 2/ c ) and 4 ( P 1̄) are linear 1D coordination polymers. The uncoordinated 4,4′-azobipyridine in the lattice is responsible for the conversion of these 1D coordination polymers into 3D supramolecular assemblies through O–H⋯N hydrogen bonding interactions between coordinated water and N-centers of an azopy ligand. Similar reactions carried out using 1,2-bis(4-pyridyl)ethylene (bpe) as the linker yielded compounds having the formula {[M(dtbp) 2 (bpe)(H 2 O) 2 ]·(bpe)} x (M = Mn ( 5 ); Co ( 6 ); Cu ( 7 ); Ni ( 8 )). Compounds 5–8 have been characterized by analytical and spectroscopic methods. Preliminary single crystal X-ray diffraction studies carried out on poorly diffracting crystals of 5 and 6 establish their isostructural nature to 1–4 , also displaying a similar supramolecular aggregation behaviour. A longer ditopic N , N ′-donor ligand, 1,2-bis(pyridin-3-ylmethylene)hydrazine (bph), has been used in place of bpe/azoby to synthesize 1-dimensional coordination polymers [{M(bph)(H 2 O) 4 }{(dtbp) 2 }] (M = Ni ( 9 ) and M = Co ( 10 )) and [Cd(bph) 3 (dtbp) 2 ] n ( 11 ) which have completely different structural motifs when compared to 1–4 .