Partial Molal Volumes and Volume Changes for Complex Formation of [M(phen)3]Cl2 in Aqueous Solutions

Abstract

Abstract The partial molal volumes, \barV°, of [M(phen)3]Cl2 (M=Fe(II), Co(II), Ni(II), Cu(II), and Zn(II)) and 1,10-phenanthroline were determined from density measurements at 25 °C. From the values for \barV° of [M(phen)3]2+, M2+ and phen the volume changes for complex formation of [M(phen)3]2+, Δ\barV°, were caluculated. Values for \barV° of [M(phen)3]Cl2 varied from 445.1 cm3 mol−1 for [Fe(phen)3]Cl2 to 458.1 cm3 mol−1 for [Zn(phen)3]Cl2 and were in the order, [Fe(phen)3]2+<[Co(phen)3]2+>[Ni(phen)3]2+<[Cu(phen)3]2+<[Zn(phen)3]2+. The Δ\barV° of [Fe(phen)3]2+ was significantly small, 4.7 cm3 mol−1. While those of other metal chelate ions were similar values, ca. 20 cm3 mol−1. The smaller Δ\barV° of [Fe(phen)3]2+ is considered to be due to the spin change from the high-spin aqua ion, [Fe(OH2)6]2+, to the low-spin complex ion, [Fe(phen)3]2+.