Deng, Yuan-Fu, et al. Journal of Coordination Chemistry 62.5 (2009): 778-788.
Manganese citrate complexes are of interest as models of metalloenzyme active sites and as homogeneous precursors of well-crystallized oxide materials, and this study examined how countercations control their frameworks.
Experimental Protocol: Complexes M2n[Mn2(Hcit)2(H2O)2]n [M = NH4+ (1); K+ (2)] and [Mn(H2O)2]n[Mn2(Hcit)2(H2O)4]n·4nH2O (3) were prepared by reacting MnCl2·4H2O (1.98 g, 10 mmol) with citric acid monohydrate (2.10 g, 10 mmol) in deionized water (10 mL), adjusting pH to 4.5 with NH4OH, KOH or NaOH and holding at 60 °C for 24-48 h. Products were characterized by elemental analysis, IR (KBr, 4000-400 cm-1), X-ray crystallography (Mo-Kα) and TG-DTA (25-600 °C, 10 °C min-1).
Performance Evaluation: Complexes 1, 2 and 3 were isolated in 80%, 70% and 60% yields. Citrate binds Mn(II) tridentately through its α-hydroxyl, α-carboxylate and one β-carboxylate. As cation size decreased, the dimensionality rose from 2-D networks (1 and 2) to a 3-D framework (3), which contains a tetrahedral water pentamer with an average O···O distance of 2.765 Å. Decomposition of 1 and 3 at 500 °C produced pure Mn3O4.
Seo, Yoshiteru, et al. Contrast Media & Molecular Imaging 8.2 (2013): 140-146.