Hexagonal crystalline Magnus' green salt analogues prepared from hydroxy-functionalised Pt and Pd complexes

New Magnus' green salt (MGS) analogues, [M(dabdOH)2][MCl4]·2H2O (dabdOH = (2S,3S)-2,3-diaminobutane-1,4-diol; M = Pd (1) and M = Pt(2)), in which [M(dabdOH)2]2+ and [MCl4]2- are stacked alternately to form linear chains, were obtained as hexagonal plate crystals. The hexagonal shape and large crystal size are unprecedented features as MGS analogues. An unusual trigonal grade separation of chain complexes has been revealed by the structural analysis. 1 and 2 exhibited remarkable yellow and pink colours, respectively, which are derived from weak M⋯M interactions. The dabdOH ligand, which has an additional hydrogen donor group (hydroxy group), produces a multiple-hydrogen-bond network. The combination of intrachain and interchain hydrogen bonds gives a two-dimensional (2D) hydrogen-bond sheet, and each 2D sheet is indirectly connected by hydrogen bonds via lattice water molecules. The OH-functionalised ligand greatly increases the hydrophilicity of the MGS analogues and yields the largest single crystals of all MGS analogues reported so far. The trigonal grade-separated chain structure is likely due to the geometric matching between the periodicity of chains and the short axis width of the chain. This strategy opens up new insight for preparing large crystals of MGS analogues and for constructing trigonal grade-separated nanowires in molecular crystals.

Interdigitated Pt-Br chains with π-stacking: an approach toward Robin-Day class I mixed valency in MX-chain complexes

The first interdigitated MX-type chain complex with infinite π-stacked arrays was synthesized. The synchronization between a Pt-Br⋯ chain and π-stacking periodicities led to the longest M-X-M distance (6.6978(15) Å) and nil or negligible intervalence charge transfer, which is essential to realize the Robin-Day class I mixed valence state in MX chains.

An unusual Pd(III) oxidation state in the Pd-Cl chain complex with high thermal stability and electrical conductivity

The Pd(iii) oxidation state is unusual and unstable since it strongly tends to disproportionate. We synthesized the quasi-one-dimensional (1D) halogen-bridged Pd(iii)-Cl complex [Pd(dabdOH)2Cl]Cl2 (1-Cl; dabdOH = (2S,3S)-2,3-diaminobutane-1,4-diol) with multiple hydrogen bonds. From single-crystal X-ray diffraction, the bridging Cl- ions were located at the midpoint of the Pd-Cl-Pd moieties in the 1D chains, indicating that the Pd ions are in a Pd(iii) average valence (AV) state. Moreover, bright spots for the Pd(iii) dz2 orbitals in the upper Hubbard band above the Fermi level were observed every ∼5 Å using scanning tunnelling microscopy. These results clearly indicate that the Pd ions are in a Pd(iii) AV state in 1-Cl. In addition, 1-Cl has the highest thermal stability (470 K) among the Pd(iii) complexes reported and the highest electrical conductivity (0.6 S cm-1 at 300 K) among the 1D Pd-Cl chains reported so far.

Proton Conductivity via Trapped Water in Phosphonate-Based Metal-Organic Frameworks Synthesized in Aqueous Media

Metal-organic frameworks (MOFs) are promising candidates for proton-conducting applications. Herein, we report the aqueous synthesis of two new phosphonate-based MOFs comprising glyphosate linkers, [Mg(dpmp)]·2H₂O (Mg-NU-225) and [Fe(dpmp)]·2H₂O (Fe-NU-225), (dpmp = N,N'-diphosphonomethyl-2,5-piperazinedione), and explore their proton conductivities. Single crystal X-ray diffraction measurements revealed that both frameworks display a two-dimensional layered structure with a cyclic ring ligand which forms in situ from the condensation of two glyphosate molecules. Under humid conditions and over a wide temperature range, water molecules are trapped between adjacent layers and facilitate rapid proton conduction. Mg-NU-225 and Fe-NU-225 recorded proton conductivities of 1.5 × 10^-5 and 1.7 × 10^-5 S cm^-1, respectively, along the plane direction and 1.6 × 10^-3 and 9.1 × 10^-5 S cm^-1 perpendicular to the plane direction at 55 °C and 95% relative humidity, as confirmed by two-contact probe impedance methods. The mechanism of proton transport was found to be that of the Grotthuss model from the low activation energy for proton hopping.

Control of the Porosity in Manganese Trimer-Based Metal-Organic Frameworks by Linker Functionalization

Manganese complexes have attracted significant interest in chemical industries and academic research for their application as catalysts owing to their ability to attain a variety of oxidation states. Generally, sterically bulky ligands are required to isolate molecular homogeneous catalysts in order to prevent decomposition. Herein, we capitalize on the catalytic properties of Mn and circumvent the instability of these complexes through incorporation of Mn-atoms into porous crystalline frameworks, such as metal-organic frameworks (MOFs). MOFs are able to enhance the stability of these catalysts while also providing accessibility to the Mn sites for enhanced reactivity. We solvothermally synthesized two trinuclear Mn-based MOFs, namely [Mn₃O(BDC)₃(H₂O)₃]_n (Mn-MIL-88, where H₂BDC = benzene-1,4-dicarboxylic acid) and [Mn₃O(BDC-Me₄)₃(H₂O)₃]_n (Mn-MIL-88-Me₄, where H₂BDC-Me₄ = 2,3,5,6-tetramethylterephthalic acid). Through comprehensive single-crystal X-ray diffraction, spectroscopic, and magnetic studies, we revealed that both MOFs are in a Mn(II/III) mixed-valence state instead of the commonly observed Mn(III) oxidation state. Furthermore, the use of a methylated linker (BDC-Me₄) allowed access to permanent porosity in Mn-MIL-88-Me₄, which is an analogue of the flexible MIL-88 family, yielding a catalyst for alcohol oxidation.

Conductive zigzag Pd(iii)–Br chain complex realized by a multiple-hydrogen-bond approach

Coexistence of zigzag structure and the uncommon Pd(iii) oxidation state in quasi-1D halogen-bridged metal complexes was realized in a conductive Br-bridged Pd chain complex, [Pd(dabdOH)₂Br]SO₄·3H₂O (2), for the first time.

MX-type single chain complexes with an aromatic in-plane ligand: incorporation of aromatic interactions for stabilizing the chain structure

MX-type one-dimensional complexes [Pt^IV(amp)₂Br₂][Pt^II/IV(amp)₂Br]₂(HSO₄)₂(SO₄)₂·13H₂O (3) and [Pt^IV(amp)₂Br₂][Pt^II/IV(amp)₂Br]₂(H₂PO₄)₆·8H₂O (4) were synthesized as the first analogue containing only an aromatic in-plane ligand. The Pt-Br chain structures of 3 and 4 are stabilized by both the hydrogen-bond network along the chain and the π-stacking via intercalated Pt(iv) complexes. Structural and spectroscopic studies indicated that both 3 and 4 form the Pt(ii/iv) mixed valence state.

Smallest Optical Gap for Pt(II)-Pt(IV) Mixed-Valence Pt-Cl and Pt-Br Chain Complexes Achieved by Using a Multiple-Hydrogen-Bond Approach

A multiple-hydrogen-bond approach was applied to shorten Pt-X-Pt distances in Cl- and Br-bridged Pt chain complexes. [Pt(dabdOH)₂Cl]Cl₂ (5) and [Pt(dabdOH)₂Br]Br₂ (6) (dabdOH = (2 S,3 S)-2,3-diaminobutane-1,4-diol) contain hydroxy groups, which form additional hydrogen bonds with counteranions. 5 has the shortest Pt-Cl-Pt distance (5.0747(8) Å) of all Cl-bridged Pt chain complexes reported to date. Furthermore, the smallest optical gap (1.45 eV for 5 and 1.19 eV for 6) in any Cl- or Br-bridged Pt chain complex was achieved. 6 has the highest electrical conductivity (1.9 × 10^-5 S cm^-1 at room temperature) of all Br-bridged Pt chain complexes. This study shows that the introduction of additional hydrogen bonds between the ligands and halides is effective to enhance the electronic properties of halogen-bridged metal complexes.