Facile synthesis of paramagnetic Co(II)-hexaborate(2-)-based semi-organic complexes: a combined investigation on X-ray crystal structure, Hirshfeld surfaces analysis, optical and magnetic properties

Two new paramagnetic hybrid cobalt(II)-hexaborate(2-)-based semi-organic complexes: (2A3MP) 2 [Co{κ 3 O–B 6 O 7 (OH) 6 } 2 ].2H 2 O ( 1 ) and (2A4MP) 2 [Co{κ 3 O–B 6 O 7 (OH) 6 } 2 ].2H 2 O ( 2 ) (2A3MP = 2-amino-3-methylpyridinium, 2A4MP = 2-amino-4-methylpyridinium) have been obtained and characterized by X-ray diffraction, FT-IR, TG–DTA, optical and magnetic measurements. X-ray diffraction revealed two isostructural compounds based on Co(II) complexes of bis(κ 3 O-donor hexaborate(2-)) ligands, [Co{κ 3 O–B 6 O 7 (OH) 6 } 2 ] 2− , differing only in the organic counter cation. The hydrated oxidopolyborate anions are extensively H-bounded to form 3D-porous supramolecular anionic frameworks. In both 1 and 2 isostructures, 2A3MP and 2A4MP cations are present in the created voids of the inorganic frameworks through a set of H-bonds with 58.5 and 60.5% H…O/O…H intercontact contributions, respectively, for 1 and 2 as confirmed by Hirshfeld surfaces analysis. The optical band gap of Co(II) complexes ranges between 2.72 and 2.82 eV. Both compounds exhibited well-resolved paramagnetic properties with magnetic susceptibility values ranging between 0.9552 cm 3 mol −1 (at 2 K) and 0.0088 cm 3 mol −1 (at 300 K), typical of octahedral Co(II) complexes.