Single-Crystal to single-crystal copolymerization in a Pt(acac)2•TCNQ cocrystal with new TCNQ reactivity and coordination mode

TL;DR

A new single-crystal to single-crystal reaction forms a unique organometallic copolymer with a novel coordination mode of TCNQ.

Contribution

The study reveals a new reactivity and coordination mode of TCNQ in a Pt-based cocrystal through a solid-state oxidative addition reaction.

Findings

A single-crystal to single-crystal reaction forms a one-dimensional organometallic copolymer.

TCNQ adopts a new dianionic coordination mode, binding to two Pt centers.

The Pt(II) center is oxidized to Pt(IV) and becomes six-coordinate in the copolymer.

Abstract

We report new results involving an unprecedented single-crystal to single-crystal reaction in charge transfer cocrystals of neutral TCNQ with a neutral planar coordination compound of Pt(II).

TCNQ (7,7,8,8-tetracyanoquinodimethane, C12H4N4) is a flat, easily reduced molecule that can form cocrystals exhibiting charge transfer between the TCNQ and its coformer.

A simple Pt coordination compound [Pt(II)(acac)2] (acac is acetylacetonate, C H O -) forms a cocrystal5with7 2 neutral TCNQ. Some forms of stimulus provoke a solid-state oxidative addition reaction in the cocrystal, in which an organometallic copolymer is formed, catena-[Pt(IV)(acac)2-μ(TCNQ2-)]n. The prominent feature of the structure of the [Pt(acac)2]•TCNQ cocrystal, 1, Fig. 1, is a column of alternating coplanar molecules of the two components, with a slight tilt between the propagation direction of the column and the direction perpendicular to the plane of the molecules.

Following the single-crystal to single-crystal reaction to form 2, Fig. 2, the columns of independent molecules are replaced by a one-dimensional copolymer in which each Pt center has undergone Pt-C bond formation. The two Pt-C bonds are trans to each other, and the four- coordinate Pt(II) center of [Pt(acac)2] has been oxidized to Pt(IV) and is six-coordinate in the polymer. Each TCNQ is coordinated to two different Pt centers through what were the exocyclic sp2-hybridized C7 and C8 of the original TCNQ. These C atoms are sp3 hybridized in the copolymer, breaking the planarity of the TCNQ, Fig. 2. TCNQ(2-), now dianionic, presents a new coordination mode. This and other features of the reaction and the product will be discussed.