Multiple-Hydrogen-Bond Approach to Uncommon Pd(III) Oxidation State: A Pd–Br Chain with High Conductivity and Thermal Stability

Abstract

A Br-bridged Pd chain complex with the Pd ion in an uncommon +3 oxidation state, [Pd(dabdOH)Br]Br (3), was prepared using a new method involving multiple hydrogen bonds. The PdBr chain complex exhibited superior electrical conductivity and thermal stability. An in-plane ligand with an additional hydrogen donor group (hydroxy group), (2S,3S)-2,3-diaminobutane-1,4-diol (dabdOH), was used to create a multiple-hydrogen-bond network, which effectively shrinks the Pd-Br-Pd distance, stabilizing the Pd(III) state up to its decomposition temperature (443 K). 3 shows semiconducting behavior with quite high electrical conductivity (3-38 S cm at room temperature), which is 10 times larger than the previous record for analogous PdBr chains. Indeed, 3 is the most conductive MX-type chain complex reported so far. The precise positional control of ions via a multiple-hydrogen-bond network is a useful method for controlling the electronic states, thermal stability and conductivity of linear coordination polymers.

Multiorbital antiferromagnetic metal induced by intramolecular self-doping

“…This has long been the only way to generate conducting electrons in molecular crystals. The successful synthesis of crystals composed of a single molecular species, M(tmdt) 2 with a transition-metal ion M [9,10], opened a route to molecule-based electronic conductors in the field of widely studied metal-complex systems such as (DCNQI) 2 Cu, the tetracyanoplatinates, and halogen-bridged complexes [11][12][13][14]. Remarkably, their electronic structure contains several frontier molecular orbitals with discrete characters; some carry the nature of the d orbitals of M, but are strongly hybridized with the surrounding sulfur p orbitals, and the others are the pπ orbitals mostly originated from the ligands, tmdt's [15,16].…”

Structural Study of Bromide‐Bridged Pd Chain Complex with Weak CH···O Hydrogen Bonds

“…The Pd chain complexes in MV state show Raman signals characteristic of X –Pd IV – X symmetrical stretching modes [ν( X –Pd IV – X )] , , . On the other hand, those in AV state do not show such Raman signals because the centered Br – between two neighboring Pd ions makes the signal of ν( X –Pd III – X ) forbidden , , , . In the polarized Raman spectrum of 2 , the signal attributable to ν(Br–Pd IV –Br) was observed around 150 cm –1 at room temperature (Figure ), supporting that 2 is in Pd II /Pd IV MV state.…”

“…Finally, we discuss the ligand arrangements and hydrogen bonding systems of 1 and 2 . The hydrogen bonds play an important role in stabilizing the chain structure and controlling the electronic state of MX chains . Figure a and b shows the hydrogen bonds between amino groups of in‐plane ligands and counteranions in 2 and 1 , respectively.…”

“…The unique conducting and intrinsic optical properties of MX chains motivate us to synthesize new MX chains with unusual electronic states. For example, many efforts have been made to achieve Pd III AV state . Because AV state can be stabilized by shrinking M–X–M distance, the attractive force between alkyl chains of the counteranions (so‐called fastener effect) have been introduced as the chemical pressure .…”

“…Recently, we have reported a new strategy, so‐called multiple‐hydrogen‐bond approach, to realize uncommon Pd III oxidation state in PdBr chain complex, [Pd(dabdOH) 2 Br]Br 2 ( 1 ) . We designed a new in‐plane ligand (2 S ,3 S )‐2,3‐diaminobutane‐1,4‐diol (dabdOH) (Scheme a), to create an additional hydrogen bond network by introducing hydroxy groups.…”