Heterobimetallic Lantern Complexes and Their Novel Structural and Magnetic Properties

Abstract

As the scale of microelectronic circuit devices approaches the atomic limit, the study of molecular-based wires and magnets has become more prevalent. Compounds with quasi-1D geometries have been investigated for their electronic conductivity and magnetic properties with potential use as nanoscale circuit components and information storage devices. To increase the number of compositionally tailored molecular systems available to study, we have taken a building-block, bottom-up approach to the development of improved electronic structure and magnetic properties of quasi-1D arrays. Over the past decade, a large family of asymmetric complexes that can assemble into extended arrays has resulted. Lantern (or paddle-wheel) complexes with conventional {O, O} donor carboxylates are legion, but by the use of monothiocarboxylate ligands and hard-soft Lewis acid-base principles, dozens of new lantern complexes of the form [PtM(SOCR)(L)] (M = Mg, Ca, Cr, Mn, Fe, Co, Ni, Zn; R = Ph (tba = thiobenzoate), CH (SAc = thioacetate); L = neutral or anionic ligand) have been prepared. Depending on M and L, new intermolecular arrangements have resulted, and the magnetic properties have proven particularly interesting. In the solid state, the [PtM(SOCR)(L)] building blocks are sometimes isolated, sometimes form dimers, and can be induced to form infinite chains. The versatility of the lantern motif was demonstrated with a range of axial ligands to form both terminal and bridged complexes with various 3d metals and two different substituted thiocarboxylate backbone ligands. Within the dozens of crystallographically characterized compounds that make up this family of lanterns, several different structural motifs of solid-state dimerization were observed and divided into four distinct categories on the basis of their Pt···Pt and Pt···S distances and relative monomer orientations. Among all of these compounds, three novel magnetic phenomena were observed. Initially, long-range antiferromagnetic coupling between two metals more than 8 Å apart was observed in solid-state dimers formed via metallophilic Pt···Pt interactions and could induced by choice of the terminal L group. An infinite chain was prepared in [PtCr(tba)(NCS)] that displays ferromagnetic coupling between Cr centers with J/ k = 1.7(4) K. Homobimetallic quasi-1D chains of the form [Ni(SOCR)(L)] (R = Ph, CH; L = DABCO, pyz) were also prepared with S = 1 {Ni} building blocks in which the Ni centers have two different spin states with weak antiferromagnetic coupling along the chain, such that -0.18 > J/ k > -0.24 K. In the [Ni(tba)(quin)] derivative, a solid-state dimer forms with a bridging square conformation by interlantern NiS interactions and displays unusual S = 1 configurations on both Ni centers and weak antiferromagnetic coupling between them.

Hard–Soft Chemistry Design Principles for Predictive Assembly of Single Molecule-Metal Junctions

“…To test a range of hard−soft intramolecular interactions, we use hetero-and homobimetallic lantern complexes, which provide a synthetically tunable ligand framework and independent choice of two metal atoms, in the heterobimetallic case. 30 By synthetically varying different components of the lanterns and performing STMBJ conductance measurements, we systematically identify which intramolecular metal−ligand bonding schemes are compatible with Au electrodes. Our combined conductance and DFT calculations show that Lewis acid−base design principles used in synthesis also govern stability of complexes on Au.…”

Deciphering Cryptic Behavior in Bimetallic Transition-Metal Complexes with Machine Learning

“…Heterobimetallic complexes are promising because they open a vast chemical space beyond their monometallic counterparts to explore new properties and reactivities. Double decker ligands have been demonstrated [20][21][22] to constrain two metal atoms (e.g., first-row transition metals 22 ) in close proximity, enabling the controlled, combinatorial-like synthesis of a range of metal-metal complexes that exhibit desirable catalytic properties. [23][24][25][26] Nevertheless, the rational or first-principles design [27][28][29] of such complexes is challenged by the complex relationship between the metal identities and their spin state or degree of bonding.…”

“…Transition-metal complexes inhabit a large, challenging region of chemical space that holds great promise for the design of functional (e.g., magnetic) materials − and to address outstanding challenges in catalysis − and energy storage. , Heterobimetallic complexes open an even vaster chemical space beyond their monometallic counterparts to explore new properties and reactivities. Double-decker ligands have been demonstrated − to constrain two metal atoms (e.g., first-row transition metals) in close proximity enabling the controlled, combinatorial-like synthesis of a range of metal–metal complexes that exhibit desirable catalytic properties. − Nevertheless, the rational or first-principles design − of such complexes is challenged by the complex relationship between the metal identities and their spin state or degree of bonding. In particular, the formal shortness ratio (FSR), , which is the ratio of the observed bond length relative to the bond length expected for a single metal–metal bond (i.e., sum of Pauling radii), has been proposed as a measure of the strength of bonding in complexes that can vary widely depending on differences in the metal group number and the d electron count .…”

Perfect Spin Filtering in Homobimetallic Ni Complex with High Tolerance to Structural Changes

“…Bimetallic lantern complexes can exhibit different d-orbital splitting in two transition metal ions separately and diverse physical properties depending on the coordination environment and coupling between two central transition metal atoms. Since the first bimetallic metal building block, [Cu 2 (OAc) 4 ·2H 2 O], was synthesized, hundreds of lantern complexes with four O,O-carboxylate ligands have been reported with homobimetallic and heterobimetallic combinations. − Some dimers and one- or quasi-one-dimensional chains have also been synthesized, some of which exhibit unique characteristics, such as long-range antiferromagnetic coupling. , …”

“…23 32−34 Some dimers and one-or quasi-one-dimensional chains have also been synthesized, some of which exhibit unique characteristics, such as long-range antiferromagnetic coupling. 35,36 In this Letter, we propose a new perspective on the stability of spin polarization in a homobimetallic lantern complex, [Ni 2 (SOCH) 4 (NCS) 2 ]. We also report the spin-resolved transport properties of its molecules with different lengths sandwiched between two gold electrodes with the aim of providing a new method for the design of the spintronic devices with stable spin-polarized characteristics.…”