H-bonding directed formation of 1D-single chains, 2D-sheets, and 3D structures in magnetically coupled tetranuclear nickel(II) complexes with incomplete double cubane core

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

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 Co^IICo^III: [Co₂^III(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), [Co₂^IICo₂^III(HL⁻²)₂(µ-CH₃CO₂)₂(µ₃-OH)₂](NO₃)₂·2CH₃CH₂OH (3), and [Co₂^IICo₂^III (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 [Co₂^IICo₂^III(HL⁻²)₂(µ-CH₃CO₂)₂(µ_3-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 [Co₂^IICo₂^III (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.

Self-Assembly of Antiferromagnetically-Coupled Copper(II) Supramolecular Architectures with Diverse Structural Complexities

The self-assembly of 2,6-diformyl-4-methylphenol (DFMP) and 1-amino-2-propanol (AP)/2-amino-1,3-propanediol (APD) in the presence of copper(II) ions results in the formation of six new supramolecular architectures containing two versatile double Schiff base ligands (H₃L and H₅L1) with one-, two-, or three-dimensional structures involving diverse nuclearities: tetranuclear [Cu₄(HL²⁻)₂(N₃)₄]·4CH₃OH·56H₂O (1) and [Cu₄(L³⁻)₂(OH)₂(H₂O)₂] (2), dinuclear [Cu₂(H₃L1²⁻)(N₃)(H₂O)(NO₃)] (3), polynuclear {[Cu₂(H₃L1²⁻)(H₂O)(BF₄)(N₃)]·H₂O}_n (4), heptanuclear [Cu₇(H₃L1²⁻)₂(O)₂(C₆H₅CO₂)₆]·6CH₃OH·44H₂O (5), and decanuclear [Cu₁₀(H₃L1²⁻)₄(O)₂(OH)₂(C₆H₅CO₂)₄] (C₆H₅CO₂)₂·20H₂O (6). X-ray studies have revealed that the basic building block in 1, 3, and 4 is comprised of two copper centers bridged through one μ-phenolate oxygen atom from HL²⁻ or H₃L1²⁻, and one μ-1,1-azido (N₃⁻) ion and in 2, 5, and 6 by μ-phenoxide oxygen of L³⁻ or H₃L1²⁻ and μ-O²⁻ or μ₃-O²⁻ ions. H-bonding involving coordinated/uncoordinated hydroxy groups of the ligands generates fascinating supramolecular architectures with 1D-single chains (1 and 6), 2D-sheets (3), and 3D-structures (4). In 5, benzoate ions display four different coordination modes, which, in our opinion, is unprecedented and constitutes a new discovery. In 1, 3, and 5, Cu(II) ions in [Cu₂] units are antiferromagnetically coupled, with J ranging from −177 to −278 cm⁻¹.

Azido-Cyanide Mixed-Bridged FeIII-NiII Complexes

The successful introduction of azide ions as secondary bridges into the Fe^III-Ni^II cyanide system afforded two clusters and one unique 4(3),2-ribbon chain: [(bpzpy)₂Ni₂(μ₂-1,1-N₃)₂{(pzTp)Fe(CN)₃}₂]·3H₂O [1; bpzpy = 2,6-bis(pyrazol-1-yl)pyridine, and pzTp = tetrakis(pyrazolyl)borate], [(L1)₂Ni₄(μ₃-1,1,1-OCH₃)₂(μ₂-1,1-N₃)₂(H₂O)₂{(Tp)Fe(CN)₃}₂]·2CH₃OH·H₂O [2; Tp = hydrotris(pyrazolyl)borate, and HL1 = 2,6-bis{(2-hydroxypropylimino)methyl}-4-methylphenol], and [(L2)₂Ni₃(μ₂-1,1-N₃)₄{(pzTp)Fe(CN)₃}₂]_n (3; L2 = 2-{[phenyl(pyridin-2-yl)methylene]amino}ethan-1-amine). Both 1 and 2 feature the centrosymmetric {Fe^III-Ni^II₂-Fe^III} and {Fe^III-Ni^II₄-Fe^III} rodlike structures in which the two peripheral [(Tp^R)Fe(CN)₃]^- anions act as monodentate ligands via one cyanide group to link the central azide-bridged [Ni₂] and [Ni₄] subunit, respectively, while 3 displays an extended structure of the double-zigzag (4,2-ribbon) chain in which the double end-on azide-bridged trinuclear [Ni₃] subunits serve as the 4-connected nodes. Magnetic study revealed that intramolecular ferromagnetic coupling is dominated by the azide or cyanide bridges in all of the complexes. Remarkably, complex 1 behaves as a single-molecule magnet with an effective energy barrier of 16.5 cm^-1 at zero dc field, while complex 3 exhibits metamagnetism with a hidden spin canting property below 12 K.

Impact of Group 10 Metals on the Solvent-Induced Disproportionation of o-Semiquinonato Complexes

The oxidation of [M^II (3,5-DTBCat)(DTBbpy)] (M=Ni ([Ni]), Pd ([Pd]), and Pt ([Pt]); 3,5-DTBCat=3,5-di-tert-butylcatecholato; DTBbpy=4,4'-di-tert-butyl-2,2'-bipyridine) afforded the dimeric {[Ni^II (3,5-DTBSQ)(DTBbpy)](PF₆ )}₂ ({[Ni](PF₆ )}₂ ; 3,5-DTBSQ=3,5-di-tert-butylsemiquinonato) and monomeric semiquinonato (SQ) complexes [M^II (3,5-DTBSQ)(DTBbpy)](PF₆ ) (M=Pd ([Pd](PF₆ )) and Pt ([Pt](PF₆ ))). The negative solvatochromic properties of the SQ complexes allowed us to estimate the relative order of their dipole moments: [Pd](PF₆ )>[Pt](PF₆ )>{[Ni](PF₆ )}₂ . The complexes [Pd](PF₆ ) and [Pt](PF₆ ) adopt monomeric structures and are stable in CH₂ Cl₂ and toluene, whereas they gradually disproportionate at room temperature to [M] and 3,5-di-tert-butylbenzoquinone (3,5-DTBBQ) in polar solvents such as THF, MeOH, EtOH, DMF, or DMSO. The results of spectroscopic studies suggested that the oxidized nickel complex adopts a monomeric structure ([Ni](PF₆ )) in CH₂ Cl₂ , but a dimeric structure ({[Ni](PF₆ )}₂ ) in the other investigated solvents. In polar solvents, {[Ni](PF₆ )}₂ may disproportionate to [Ni] and 3,5-DTBBQ at 323 K, thereby demonstrating a significant solvent- and metal-dependence in temperature. The relative activities of {[Ni](PF₆ )}₂ and [M](PF₆ ) toward disproportionation are related to the electrochemically estimated K_dis values in CH₂ Cl₂ and DMF. The present work demonstrates that solvent polarity and the dipole moments of the SQ complexes promote disproportionation, which can be controlled by a judicious choice of the metal ion, solvent, and temperature.