Channeled Polymorphs of cis-M(CNPh)₂Cl₂ (M = Pt, Pd) With Extended Metallophilic Interactions

Abstract

Two distinct polymorphs of cis-M(CNPh)2Cl2 (M = Pt,Pd) were obtained under different crystallization conditions. One polymorph of each compound contains 3−4 Å-wide, vacant channels stabilized by a synergistic combination of extended metallophilic interactions and ligand π−π stacking, whereas the other polymorph contains no discernible void space and only isolated, longer metal−metal contacts. The channeled polymorphs are favored under faster crystal growth conditions, and face-indexing revealed that the growth axes are along the M···M chains. Although the channels extend the length of a crystal, they do not absorb solvent because of their narrow widths.

Structural and Luminescence Studies on π···π and Pt···Pt Interactions in Mixed Chloro-Isocyanide Cyclometalated Platinum(II) Complexes†

“…One of them contains vacant channels that are stabilized by a combination of extended Pt 3 3 3 Pt interactions and π 3 3 3 π stacking. 56 Pt(II) complexes bearing cyclometalated and isocyanide ligands have revealed interesting photophysical properties, 24,27,28,57 including low-energy emissions in fluid solution. Along these lines, we have recently described the synthesis of the isocyanide benzoquinolate Pt(II) complexes [Pt(bzq)(CNR) 2 ]X (R = t Bu, Xyl, 2-Np; X = ClO 4 -, PF 6 -) and the influence of the counteranion and concentration on their luminescent properties.…”

Interplay of Metallophilic Interactions, π–π Stacking, and Ligand Substituent Effects in the Structures and Luminescence Properties of Neutral PtIIand PdIIAryl Isocyanide Complexes

“…19 The channels appear to be stabilized by a synergistic combination of metallophilic and aryl π−π interactions. The chain form of Pt(CNPh) 2 Cl 2 is luminescent under UV excitation, whereas the previously known dimeric form 20 is nonluminescent, clearly indicating that luminescence in the compound requires extended Pt···Pt contacts.…”

“…However, these substituents also change the steric profile of the arylisocyanide, which may either disrupt or enhance the π−π stacking interactions that can synergistically stabilize extended M···M interactions in these complexes. 19 Another goal of this study is to compare the structures of identically ligated palladium and platinum complexes in order to gain insights into the relative importance of metallophilic attractions versus other packing forces. Owing to the lanthanide contraction, Pt has a very similar covalent radius to Pd 25, 26 and often forms nearly isostructural complexes, 27 but Pd experiences smaller relativistic effects that are believed to impart weaker metallophilic bonding.…”

“…Dropwise addition of dry hexanes and dry Et 2 O resulted in precipitation of a yellow crystalline solid, which was filtered, washed with dry hexanes and dry Et 2 O, and dried in vacuo overnight. Characterization data for Pd(CNC 6 H 4 -p-CF 3 ) 2 Cl 2 (2), 32 Pt-(CNPh) 2 Cl 2 (5), 19 and Pd(CNPh) 2 Cl 2 (6) 19 X-ray Crystal Structure Determinations: General. X-ray diffraction data were collected on a Bruker SMART APEX II diffractometer with a CCD detector using a combination of ϕ and ω scans.…”

“…As previously communicated, crystal growth of M(CNC 6 H 5 ) 2 Cl 2 from n-hexane/CH 2 Cl 2 provided long yellow rods of the chain forms 5a/6a, whereas slower crystal growth from chlorobenzene/cyclohexane afforded the dimer polymorphs 5b/6b. 19 Compounds 5a and 6a feature extended zigzag chains of metal atoms with short M···M contacts ( Figure 4), two "bands" of π−π interactions (Figure 5a), and void channels parallel to the metal chains (Figure 5b). The channels are walled by phenyl rings, which are canted relative to the metal coordination plane at dihedral angles of 65−73°.…”