Facile carboxylate ligand variation of heterotrimetallic 12-metallacrown-4 complexes

Synthesis Strategies and Structures of Molecular Heterometallic Oxo Clusters

Multinuclear heterometallic oxo clusters, composed of two or more different metal cations bridged by oxo ligands, represent an important class of molecular complexes known for their unique magnetic, catalytic, and electrochemical properties resulting from cooperative interactions between the metal cations. If three or more types of metal cations can be arranged as designed, their chemical and physical properties can be precisely and flexibly controlled, potentially creating innovative materials. However, research on hetero-trimetallic and hetero-tetrametallic oxo clusters remains limited. This review presents an interdisciplinary search of multinuclear heterometallic oxo clusters, regardless of the type of ligand, to explain and classify their synthesis strategies and structures. By cataloging crystallographically characterized heterometallic oxo clusters using ligand-per-metal values and synthesis method notations, valuable insights have been gained into effective synthesis methods for the precise arrangement of metal cations. The advantages and disadvantages of one-pot synthesis methods and synthesis strategies for achieving precise structural control of heterometallic oxo clusters are discussed with an emphasis on the prediction of their final structures. The insights from this review are expected to drive the development of synthetic and analytical techniques for the precise synthesis of heterometallic complexes in a predictable way.

Visible and near-infrared emitting heterotrimetallic lanthanide-aluminum-sodium 12-metallacrown-4 compounds: discrete monomers and dimers

The luminescence properties of two types of heterotrimetallic aluminum-lanthanide-sodium 12-metallacrown-4 compounds are presented here, LnNa(ben)₄[12-MC_{Al(III)N(shi)}-4] (LnAl4Na) and {LnNa[12-MC_{Al(III)N(shi)}-4]}₂(iph)₄ (Ln2Al8Na2), where Ln = Gd^III, Tb^III, Er^III, and Yb^III, MC is metallacrown, ben^- is benzoate, shi^3- is salicylhydroximate, and iph^2- is isophthalate. The aluminum-lanthanide-sodium metallacrowns formed with benzoate are discrete monomers while, upon replacement of the benzoate with the dicarboxylate isophthalate, two individual metallacrowns can be joined to form a dimer. In the solid state, the terbium version of each structure type displays emission in the visible region, and the erbium and ytterbium complexes emit in the near-infrared. The luminescence lifetimes (τ_obs) and quantum yields have been collected under ligand excitation (QLLn) for both LnAl4Na monomers and Ln2Al8Na2 dimers. Several of these values tend to be shorter (luminescence lifetimes) and smaller (quantum yields) than the corresponding values recorded for the structurally similar gallium-lanthanide monomer and dimer 12-MC-4 molecules. However, the quantum yield value recorded for the visible emitting Tb2Al8Na2 dimer, 43.9%, is the highest value observed in the solid state to date for a Tb^III based metallacrown.

Crystal structures of two heterotrimetallic dysprosium-manganese-sodium 12-metallacrown-4 complexes with the bridging ligands 3-hy-droxy-benzoate and 4-hy-droxy-benzoate

The syntheses and crystal structures for the compounds tetra-μ-aqua--tetra-kis-{2-[aza-nid-yl-ene(oxido)meth-yl]phenolato}tetra-kis-(μ2-3-hy-droxy-benzoato)dys-pro-s-ium(III)-tetra-manganese(III)sodium(I) N,N-di-methyl-acetamide deca-solvate, [DyMn4Na(C7H5O3)4(C7H4NO2)4(H2O)4]·10C4H9NO or [DyIIINa(4-OHben)4{12-MCMn(III)N(shi)-4}(H2O)4]·10DMA, 1, and tetra-μ-aqua--tetra-kis-{2-[aza-nid-yl-ene(oxido)meth-yl]phenolato}tetra-kis-(μ2-3-hy-droxy-benzoato)dys-pros-ium(III)tetra-manganese(III)sodium(I) N,N-di-methylformamide tetra-solvate, [DyMn4Na(C7H5O3)4(C7H4NO2)4(H2O)4]·4C3H7NO or [DyIIINa(3-OHben)4{12-MCMn(III)N(shi)-4}(H2O)4]·4DMF, 2, and where MC is metallacrown, shi3- is salicyl-hydroximate, 3-OHben is 3-hy-droxy-benzoate, DMA is N,N-di-methyl-acetamide, 4-OHben is 4-hy-droxy-benzoate, and DMF is N,N-di-methyl-formamide, are reported. For both 1 and 2, the macrocyclic metallacrown consists of an [MnIII-N-O] ring repeat unit, and the domed metallacrown captures two ions in the central cavity: a DyIII ion on the convex side of the metallacrown and an Na+ ion the concave side. The MnIII ions are six-coordinate with an elongated tetra-gonally distorted octa-hedral geometry. Both the DyIII and Na+ ions are eight-coordinate. The DyIII ions possess a square-anti-prismatic geometry, while the Na+ ions have a distorted biaugmented trigonal-prismatic geometry. Four 3-hy-droxy-benzoate or 4-hy-droxy-benzoate ligands bridge each MnIII ion to the central DyIII ion. For 1, whole-mol-ecule disorder is observed for the main mol-ecule, excluding only the DyIII and Na+ ions, and the occupancy ratio refined to 0.8018 (14):0.1982 (14). Three DMA mol-ecules were refined as disordered with two in general positions by an approximate 180° rotation and the third disordered twice by general disorder as well as by an exact 180° rotation about a twofold axis that bis-ects it. The occupancy ratios refined to 0.496 (8):0.504 (8), 0.608 (9):0.392 (9), and 2×0.275 (7):2×0.225 (7), respectively. For 2, segments of the metallacrown are disordered including the DyIII ion, one of the Mn ions, two of the Mn-bound 4-hy-droxy-benzoate ligands, the Mn-bridging salicyl-hydroximate ligand, and portions of the remaining three shi3- ligands. The occupancy ratio for the metallacrown disorder refined to 0.849 (9):0.151 (9). Two DMF solvent mol-ecules are also disordered, each over two orientations. The disorder ratios refined to 0.64 (3):0.36 (3) and to 0.51 (2):0.49 (2), respectively. For 2, the crystal under investigation was refined as a non-merohedric twin by a 90° rotation around the real a axis [twin ratio 0.9182 (8):0.0818 (8)].

Synthesis and crystal structure of two manganese-based 12-metallacrown-4 complexes: Na2(3-chloro-benzoate)2[12-MCMn(III)N(shi)-4](DMF)6 and MnNa(3-chloro-benzoate)3[12-MCMn(III)N(shi)-4](DMF)(H2O)4·4DMF·0.72H2O

Similar synthetic schemes yield two different metallacrown (MC) complexes: bis-(μ-3-chloro-benzoato)hexa-kis-(di-methyl-formamide)-tetra-kis-(μ4-N,2-dioxido-benzene-1-carboximidato)tetra-manganese(III)disodium(I), [Mn4Na2(C7H4ClO2)2(C7H4NO3)4(C3H7NO)6] or Na2(3-chloro-benzoate)2[12-MCMn(III)N(shi)-4](DMF)6, 1, and tetra-μ-aqua-tris-(μ-3-chloro-benzoato)(di-methyl-formamide)-tetra-kis-(μ4-N,2-dioxido-benzene-1-carboximidato)penta-manganese(III)sodi-um(I) di-methyl-formamide tetra-solvate 0.72-hydrate, [Mn5Na(C7H4ClO2)3(C7H4NO3)4(C3H7NO)(H2O)4]·4C3H7NO·0.718H2O or MnNa(3-chloro-benzo-ate)3[12-MCMn(III)N(shi)-4](DMF)(H2O)4·4DMF·0.72H2O, 2, where shi3- is salicyl-hydrox-imate and DMF is N,N-di-methyl-formamide. Both complexes have the same framework consisting of four MnIII ions in the MC ring and four shi3- ligands, resulting in an overall square-shaped mol-ecule. The MnIII ions are either five- or six-coordinate with elongated bond lengths in the apical or axial direction, respectively. The structure of 1 is nearly planar, and the MC binds two Na+ ions on opposite faces of the MC central cavity. The 3-chloro-benzoate anions also bind on opposite faces of the MC and form bridges between the central Na+ ions and the ring MnIII ions. For 1 the metallacrown mol-ecule, except for the central Na+ ion, exhibits whole mol-ecule disorder over two sets of sites. Both moieties are centrosymmetric and are related to each other by a pseudo-mirror operation with opposite sense of rotation around the Na⋯Na axis. The occupancy ratio of the main disorder of the metallacrown mol-ecules and 3-chloro-benzoate anions refined to 0.9276 (9):0.0724 (9). The structure of 2 is slightly domed, and the MC binds both an MnII ion and an Na+ ion in the MC central cavity. The MnII ion is located on the convex side of the MC, while the Na+ ion binds to the concave side. Complex 2 represents the first instance of a [12-MCMn(III)N(shi)-4] mol-ecule binding both 3d transition metal and alkali metal ions in the central cavity. In addition, three 3-chloro-benzoate anions bind on the convex side of the MC and connect the MnII ion to three of the ring MnIII ions.

Elucidation of 1H NMR Paramagnetic Features of Heterotrimetallic Lanthanide(III)/Manganese(III) 12-MC-4 Complexes

The paramagnetic one-dimensional ¹H NMR spectra of twelve Ln^IIINa^I(OAc)₄[12-MC_Mn^III(N)shi-4] complexes, where Ln^III is Pr^III-Yb^III (except Pm^III) and Y^III, are reported. Their solid-state isostructural nature is confirmed in methanol-d₄ solution, as a similar pattern in the ¹H NMR spectra is observed along the series. Notably, a relatively well-resolved spectrum is reported for the Gd^III complex. The chemical shift data are analyzed using the "all lanthanides" method, and the Fermi contact and pseudo-contact contributions are calculated for the lanthanide-induced shift (LIS). For the Tb^III-Yb^III complexes, the pseudo-contact contributions are typically 1 order of magnitude higher than the Fermi contact contributions; however, for the Gd^III complex, the Fermi contact is the main contribution to the paramagnetic chemical shift. For the methyl protons of the axial acetate (^-OAc) ligands, the LIS is opposite in sign, with respect to that of the aromatic salicylhydroximate (shi^3-) protons, because of structural rearrangements that occur upon dissociation of the Na^I cation in solution. The calculated crystal field parameters (B_Ln) for the Tb^III (360 cm^-1), Dy^III (250 cm^-1), Ho^III (380 cm^-1), Er^III (410 cm^-1), Tm^III (620 cm^-1), and Yb^III (380 cm^-1) complexes are not constant, likely as a consequence of the inaccuracy of the Bleaney's constants and, to a smaller extent, the small structural changes that occur in solution. Overall, the metallacrown scaffold retains structural integrity and similarity in solution for the entire series; however, small structural features, which do not affect the overall similarity, do likely occur.