One-Pot Self-Assembly of Dinuclear, Tetranuclear, and H-Bonding-Directed Polynuclear Cobalt(II), Cobalt(III), and Mixed-Valence Co(II)/Co(III) Complexes of Schiff Base Ligands with Incomplete Double Cubane Core.

Santokh S Tandon,Scott D Bunge,Esther C Wang,Rachel Thompson,Laurence K Thompson,Neil Patel

doi:10.3390/ma13235425

Santokh S Tandon, Scott D Bunge + Show 4 more

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https://doi.org/10.3390/ma13235425

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Abstract

The reaction of 2,6-diformyl-4-methylphenol (DFMF) with 1-amino-2-propanol (AP) and tris(hydroxymethyl)aminomethane (THMAM) was investigated in the presence of Cobalt(II) salts, (X = ClO4−, CH3CO2−, Cl−, NO3−), sodium azide (NaN3), and triethylamine (TEA). In one pot, the variation in Cobalt(II) salt results in the self-assembly of dinuclear, tetranuclear, and H-bonding-directed polynuclear coordination complexes of Cobalt(III), Cobalt(II), and mixed-valence CoIICoIII: [Co2III(H2L−1)2(AP−1)(N3)](ClO4)2 (1), [Co4(H2L−1)2(µ3-1,1,1-N3)2(µ-1,1-N3)2Cl2(CH3OH)2]·4CH3OH (2), [Co2IICo2III(HL−2)2(µ-CH3CO2)2(µ3-OH)2](NO3)2·2CH3CH2OH (3), and [Co2IICo2III (H2L12−)2(THMAM−1)2](NO3)4 (4). In 1, two cobalt(III) ions are connected via three single atom bridges; two from deprotonated ethanolic oxygen atoms in the side arms of the ligands and one from the1-amino-2-propanol moiety forming a dinuclear unit with a very short (2.5430(11) Å) Co-Co intermetallic separation with a coordination number of 7, a rare feature for cobalt(III). In 2, two cobalt(II) ions in a dinuclear unit are bridged through phenoxide O and μ3-1,1,1-N3 azido bridges, and the two dinuclear units are interconnected by two μ-1,1-N3 and two μ3-1,1,1-N3 azido bridges generating tetranuclear cationic [Co4(H2L−1)2(µ3-1,1,1-N3)2(µ-1,1-N3)2Cl2(CH3OH)2]2+ units with an incomplete double cubane core, which grow into polynuclear 1D-single chains along the a-axis through H-bonding. In 3, HL2− holds mixed-valent Co(II)/Co(III) ions in a dinuclear unit bridged via phenoxide O, μ-1,3-CH3CO2−, and μ3-OH− bridges, and the dinuclear units are interconnected through two deprotonated ethanolic O in the side arms of the ligands and two μ3-OH− bridges generating cationic tetranuclear [Co2IICo2III(HL−2)2(µ-CH3CO2)2(µ3-OH)2]2+ units with an incomplete double cubane core. In 4, H2L1−2 holds mixed-valent Co(II)/Co(III) ions in dinuclear units which dimerize through two ethanolic O (μ-RO−) in the side arms of the ligands and two ethanolic O (μ3-RO−) of THMAM bridges producing centrosymmetric cationic tetranuclear [Co2IICo2III (H2L1−2)2(THMAM−1)2]4+ units which grow into 2D-sheets along the bc-axis through a network of H-bonding. Bulk magnetization measurements on 2 demonstrate that the magnetic interactions are completely dominated by an overall ferromagnetic coupling occurring between Co(II) ions.

Highlights

Using simple building blocks, living organisms use self-assembly processes to fabricate symmetrical biomolecules, with varied levels of structural complexities [1,2,3]
Over the past thirty-five years, we have been interested in the self-assembly of polynuclear coordination complexes of transition metals to get a deeper insight into magneto-structural relationships, to understand the role of metal ions in self-assembly and structural complexities of assemblies produced, and the effects of the anions on the formation and coordination abilities of the macrocyclic and non-cyclic Schiff base ligands
In continuation of our interest in the self-assembly, structural characterization, and magnetic properties of polynuclear transition metal and lanthanide coordination complexes exhibiting ferromagnetic and antiferromagnetic spin exchange interactions, we have explored the coordination versatility of the Schiff base ligands derived from the condensation of 2,6-diformyl-4-methylphenol (DFMP) with 2-aminoethanol, 1-amino-2-propanol, 2-amino-1,3-propanediol, and tris(hydroxymethyl)aminomethane with Copper(II) [52,54,55], Cobalt(II)/Cobalt(III) [53], and Nickel(II) [53,55,56]

Summary

Introduction

Using simple building blocks, living organisms use self-assembly processes to fabricate symmetrical biomolecules (proteins, DNA, lipids, enzymes), with varied levels of structural complexities [1,2,3]. Over the past thirty-five years, we have been interested in the self-assembly of polynuclear coordination complexes of transition metals to get a deeper insight into magneto-structural relationships, to understand the role of metal ions in self-assembly and structural complexities of assemblies produced, and the effects of the anions on the formation and coordination abilities of the macrocyclic and non-cyclic Schiff base ligands Our interest in this area originated from the implications of transition metal complexes in homogeneous catalysis [24,25], as enzyme models [26,27,28,29], and their potential applications in magnetic materials [30,31,32,33,34]. In addition to polynucleating multidentate ligands, a majority of the coordination complexes involve doubly or triply bridging anions like N3 − , OH− , O2− , CH3 O− , NCS− , N(CN)2 − , CN− , and C2 H3 O2 − C6 H5 O−

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