Vol.:(0123456789) 1 3 J Inorg Organomet Polym DOI 10.1007/s10904-017-0706-6 Preparation of Co 3 O 4 Nanoparticles via Thermal Decomposition of Three New Supramolecular Structures of Co(II) and (III) Containing 4′-Hydroxy-2,2′:6′,2′′-Terpyridine: Crystal Structures and Thermal Analysis Studies Badri Z. Momeni 1  · Farzaneh Rahimi 1  · Frank Rominger 2   Received: 20 August 2017 / Accepted: 13 October 2017 © Springer Science+Business Media, LLC 2017 crystalline 1–3 to form supramolecular networks. The ther- mal stabilities of the cobalt complexes reveal that the loss of free terpyridine ligand could not be observed in low tem- peratures. The hexagonal and spherical Co 3 O 4 nanoparticles (NPCs) were prepared by direct calcination of complexes 1–3 at 600 °C in air. The nanostructures of the products were characterized by IR, powder X-ray difraction, feld emission scanning electron microscopy and energy-dispersive X-ray spectroscopy which show the purity of the resulting Co 3 O 4 NPCs. The average particle size using Scherrer’s equation is calculated to be about 32–35 nm. Keywords Cobalt · Terpyridine · Crystal structure · Co 3 O 4 NPCs · Thermal analysis 1 Introduction Transition metal complexes of 2,2′:6′,2′′-terpyridine ligand have been studied extensively since the ligand was frst reported at 1932 by Morgan and Burstall [1]. A vast num- ber of methods are known for the preparation of substi- tuted terpyridines. Most of these methods are based on the 2-acetyl pyridines and aryl aldehydes [2–5]. 4-Sub- stituted-2,6-diacetylpyridines have been used to prepare 2,2′:6′,2"-terpyridine functionalized at C 4′ and containing substituents at C 4 , C 5 and C 6 of both terminal pyridines [6]. Terpyridine complexes of transition metals such as cobalt have attracted considerable interest due to their applica- tions in medicinal chemistry, catalysis, crystal engineering and supramolecular chemistry [7–12]. The use of ligands with multiple-metal binding domains is of particular inter- est, since they can be linked by a metal-containing moiety instead of an organic group, such as 4′ -pyridyl, carboxylic acid, hydroxy or 4′-carboxyphenyl-2,2′:6′,2′′-terpyridines Abstract Three cobalt(II) and (III) complexes based on the 4′-hydroxy-2,2′:6′,2"-terpyridine (tpyOH) have been synthe- sized and structurally characterized by X-ray crystallogra- phy. The reaction of tpyOH with CoCl 2 ·6H 2 O in a mixture of methanol/CH 2 Cl 2 resulted in the formation of the new complex [Co II Cl 2 (tpyOH)] (1). On the other hand, the reac- tion of CoCl 2 ·6H 2 O with tpyOH in a 2:1 or 1:1 mol ratio in methanol under refux condition afords the new complexes [Co III (tpyOH)(tpyO)][Co II Cl 4 ]·H 2 O (2) and [Co III Cl 2 (H 2 O) (tpyO)]·H 2 O (3), respectively. Moreover, the treatment of a methanolic solution of CoCl 2 ·6H 2 O with tpyOH in a branched tube at 60 °C resulted in the formation of three quality crystals of the complexes 1 and 2 as the major prod- ucts as well as the complex 3 as a minor product. The crystal structure of [CoCl 2 (tpyOH)] (1) reveals that the cobalt(II) is penta-coordinated by two Cl − and three nitrogen atoms of tpyOH in a distorted square pyramidal geometry. The com- plex [Co III (tpyOH)(tpyO)][Co II Cl 4 ]·H 2 O (2) is described as a highly distorted octahedral geometry [CoN 6 ] while the X-ray crystal structure of the complex [Co III Cl 2 (H 2 O)(tpyO)]·H 2 O (3) shows that cobalt(III) is hexa-coordinated in a slightly distorted octahedral geometry CoCl 2 N 3 O. Several strong noncovalent interactions are present in the crystal structure of 1–3. The hydrogen bonding in 1 involves the OH⋯Cl bridges while there is a hydrogen bonding between tpyO and tpyOH of the next molecule in 2 and hydrogen bridges and π–π interactions for 3, connecting molecules and ions in the * Badri Z. Momeni momeni@kntu.ac.ir 1 Faculty of Chemistry, K.N. Toosi University of Technology, P.O. Box 16315-1618, Tehran 15418, Iran 2 Organisch-Chemisches Institut, Universität Heidelberg, 69120 Heidelberg, Germany