Spectrochimica Acta Part A 75 (2010) 1177–1180 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Substitution reactions of thorium(IV) acetate to synthesize nano-sized carboxylate complexes Balram P. Baranwal ∗ , Talat Fatma, Anand Varma, Alok K. Singh Coordination Chemistry Research Laboratory, Department of Chemistry, DDU Gorakhpur University, Gorakhpur 273 009, Uttar Pradesh, India article info Article history: Received 22 November 2008 Received in revised form 16 July 2009 Accepted 29 July 2009 Keywords: Thorium(IV) Nano-size Carboxylate Mixed-ligand complexes Polymeric abstract Some mixed-ligand thorium(IV) complexes with the general formula [Th(OOCCH 3 ) 4-n L n ] (L = anions of myristic, palmitic or stearic acid and n = 1–4) have been synthesized by the stepwise substitution of acetate ions of thorium(IV) acetate with straight chain carboxylic acids in toluene under reflux. The com- plexes were characterized by elemental analyses, spectral (electronic, infrared, NMR and powder XRD) studies, electrical conductance and magnetic susceptibility measurements. Doubly and triply bridged coordination modes of the ligands were established by their infrared spectra and nano-size of the com- plexes by powder XRD. Room temperature magnetic susceptibility measurements revealed diamagnetic nature of the complexes. Electronic absorption spectra of the complexes showed  → *, n → * and charge transfer transitions. Molar conductance values indicated the complex to be non-electrolytes. These are a new type of mixed-ligand thorium(IV) complexes for which a nano-sized, oxygen bridged polymeric structure has been established on the basis of physico-chemical studies. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Thorium, an important and first member of 5f-series elements, is known to form complexes in +4 oxidation state having different coordination numbers. However, the complexes with coordina- tion numbers 10–14 are only few [1]. This may be mainly due to steric hinderance. The interaction of thorium(IV) with organic materials has become a potential and challenging subject [2–4]. Thorium(IV) with an ionic radius 1.08 Å and a high charge (+4) ful- fils the optimum conditions required for a high coordination [5] and are an extraordinarily reactive, readily employed promotor of the hydrolysis of a variety of model phosphodiester substrates includ- ing plasmid DNA and RNA [6]. Several complexes of thorium(IV) are found useful in catalysis [7,8], sensors [9], single molecule magnets [3,6], three-dimensional connectivity [10], pathological applications (antifungal and antibacterial), pharmacological activ- ity (antitumour and cytotoxic) [11,12] as well as in analytical chemistry [13]. Literature survey revealed that an extensive work was done on carboxylate complexes with d-block metals [14–16] but a very lit- tle attention was paid on the similar derivatives of f-block metals. The organometallic actinide chemistry has received a little atten- tion recently [17–19]. It has also been noticed from the literature that no work has been done on the substitution reaction of tho- ∗ Corresponding author. Tel.: +91 551 2203459. E-mail address: drbpbaranwal@yahoo.com (B.P. Baranwal). rium(IV) acetate which may be due to its polymeric nature. With these objectives, in this paper we report the stepwise substitutions of thorium(IV) acetate to synthesize a number of mixed-ligand car- boxylates of thorium(IV). A convenient route of synthesis has been suggested and the complexes are characterized to establish their structure. The order of their solubility in non-polar solvents after stepwise substitution of acetate ion is correlated with length of the carboxylate chain. 2. Experimental 2.1. Materials and analytical methods Organic solvents (Qualigens) were dried and distilled before use by standard methods. The carboxylic acids were used after distillation under reduced pressure (m.p. of myristic acid: 53 ◦ C; palmitic acid: 63 ◦ C and stearic acid: 70 ◦ C). Thorium(IV) acetate (BDH, LR) was used as received. Thorium was determined gravi- metrically as thorium oxide [21]. The liberated acetic acid in the collected azeotrope was determined by titration with standard sodium hydroxide solution using phenolphthalein as indicator. 2.2. Physico-chemical measurements Electronic spectra were recorded on Hitachi U-2000 spectropho- tometer in chloroform, infrared spectra were recorded on Perkin Elmer 1600 series FTIR spectrophotometer in KBr discs, magnetic moment was measured on a Gouy balance using Hg[Co(SCN) 4 ] as 1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2009.07.016