Synthesis, magnetism and spectral studies of six defective dicubane tetranuclear {M₄O₆} (M = Ni^II, Co^II, Zn^II) and three trinuclear Cd^II complexes with polydentate Schiff base ligands

Abstract

A series of Ni(II), Co(II), Zn(II) and Cd(II) complexes with polytopic Schiff base ligands have been synthesized. The single-crystal X-ray crystallography results show that tetranuclear complexes have common face-shared defective dicubane cores, whereas trinuclear Cd(II) complexes are almost linear entities. Synthesis methods (solvent evaporation and hydrothermal synthesis), reaction conditions (pH, solvents and dosage) and coligands (azide, methanol, chloride and acetate) play vital roles in determining the final structure of the complexes and therefore their magnetic properties. In complexes , the terminal and central M(2+) ions are connected through mixed bridges, μ-phenoxido/μ1,1,1-X and μ-Oalphatic/μ1,1,1-X, while central two M(2+) ions are linked by double bridges, μ1,1,1-X (X = azido and methoxido groups for and respectively). For complex , two central Ni(II) ions are connected through two μ1,1,1-N3(-) which is relatively less reported. For complexes , there are two kinds of Cd(II), the centre Cd(II) ions are eight-coordinated with triangle dodecahedral geometries, while the two side Cd(II) ions are six-coordinated with trigonal prism geometries using chlorides or acetates as terminal ligands. Magnetic susceptibility measurements (χM) for compounds have been performed, and they reveal predominant ferromagnetic exchange interactions in Co(II) and Ni(II) tetramers. The photoluminescence studies show that the Zn(II) complex and three Cd(II) complexes have strong fluorescence, and the lifetimes are measured to be in the 10(2) nanosecond timescale.

Heterometallic ZnII–LnIII–ZnII Schiff Base Complexes with Linear or Bent Conformation—Synthesis, Crystal Structures, Luminescent and Magnetic Characterization

“…Compared with the free H 3 L ligand, their emissions are blue shifted (similar as in Ref. [ 11 ]). These bands can be tentatively assigned to intra ligand luminescence.…”

“…The coordination units in complexes 1 – 5 are isoskeletal but have different conformations and different intermolecular interactions. The syntheses gave as a result cationic trinuclear Zn 2 Ln coordination cores with a propeller like arrangement of the ligands ( Figure 1 ) but different from the one observed in the homotrinuclear complex of Cd II [ 11 ]. The Zn II ion occupies the N 2 O 2 cavity of the doubly deprotonated Schiff base ligand HL 2− from which the metal cation is deviated by ca.…”

“…5.39 with updates) [ 10 ] of a crystal structure of coordination compounds of this ligand. These are two homotetranuclear coordination compounds of Co II and Ni II and a homotrinuclear complex of Cd II [ 11 ]. The trinuclear complex of Cd II is reported to have photoluminescent properties with luminescence decay of the order of 10 2 ns.…”

“…The trinuclear complex of Cd II is reported to have photoluminescent properties with luminescence decay of the order of 10 2 ns. The presence of Br atom in the ligand structure (heavy halogen effect) often causes a decrease of luminescence intensity and a shift in the ligand emission position [ 11 , 12 ], but sometimes it may be beneficial for the luminescent properties as well as for the intermolecular interactions, which can stabilize the crystal structure [ 13 , 14 , 15 ]. The ligand molecules with 1,3-diamino-2-propanol bridge may undergo double or triple deprotonation forming N 2 O 2 or N 2 O 3 coordination pockets ( Table S1 ).…”

“…The ligand molecules with 1,3-diamino-2-propanol bridge may undergo double or triple deprotonation forming N 2 O 2 or N 2 O 3 coordination pockets ( Table S1 ). The doubly deprotonated ligands form classic mono- up to tetranuclear coordination compounds [ 11 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. But only the triple deprotonation enables the higher nuclearity of complexes: to hexa- [ 22 , 30 ] and heptanuclear units [ 31 ] with the use of additional anions such as nitrate or acetate.…”