New barium, strontium and strontium‐doped barium squarates: synthesis, crystal structures and DNA/BSA binding, antioxidant and in vitro cytotoxicity studies

A new set of differently hydrated barium and strontium squarates, namely poly[[triaqua(μ‐1,2‐dioxocyclobut‐3‐ene‐1,2‐diolato)barium] monohydrate], {[Ba(C 4 O 4 )(H 2 O) 3 ]·H 2 O} n ( 1 ), poly[[diaqua(μ‐1,2‐dioxocyclobut‐3‐ene‐1,2‐diolato)strontium] monohydrate], {[Sr(C 4 O 4 )(H 2 O) 2 ]·H 2 O} n ( 2 ), and poly[[triaqua(μ‐1,2‐dioxocyclobut‐3‐ene‐1,2‐diolato)barium/strontium(0.85/0.15)] monohydrate], {[Ba 0.85 Sr 0.15 (C 4 O 4 )(H 2 O) 3 ]·H 2 O} n ( 3 ), is reported. The study of their crystal structures indicates that all the complexes crystallize in the triclinic space group P . Complexes 1 and 3 have a rare combination of squarate units coordinated through monodentate O atoms to two different metal atoms and through two bidentate O atoms to three different metal atoms. Furthermore, they have three coordinated water molecules to give a coordination number of nine. The squarate ligands in complex 2 exhibit two different coordination modes: (i) monodentate O atoms coordinated to four different Sr atoms and (ii) two monodentate O atoms coordinated to two different metal atoms with the other two O atoms bidentate to four different Sr atoms. All the compounds decompose to give the respective carbonates when heated to 800 °C, as evidenced by thermogravimetry/differential thermal analysis (TG‐DTA), which are clusters of nanoparticles. Complexes 1 and 3 show additional endothermic peaks at 811 and 820 °C, respectively, indicating the phase transition of BaCO 3 from an orthorhombic (α‐ Pmcn ) to a trigonal phase (β‐ R 3 m ). All three complexes have significant DNA‐binding constants, ranging from 2.45 × 10 4 to 9.41 × 10 4   M −1 against EB‐CT (ethidium bromide–calf thymus) DNA and protein binding constants ranging from 1.1 × 10 5 to 8.6 × 10 5 with bovine serum albumin. The in vitro cytotoxicity of the complexes is indicated by the IC 50 values, which range from 128.8 to 261.3 µg ml −1 . Complex 3 shows better BSA binding, antioxidant activity against the DPPH radical and cytotoxicity than complexes 1 and 2 .