Crystal structure of catena-poly[[potassium-tri-μ-dimethylacetamide-κ6 O:O] iodide]

A one-dimensional chain formed by potassium bridged by μ2-O-dimethylacetamide is reported. This represents a small class of dimethylacetamide complexes with oxygen bridging two metal centers.


Structural commentary
The cation of title compound consists of two crystallographically independent potassium cations. Each K + cation is octahedrally coordinated by six O atoms from the DMA moieties, with each oxygen adopting a 2 -bridging mode ( Fig. 1 and Table 1). The C O distance is comparable with that in free dimethylacetamide (see Database survey). The iodide ISSN 1600-5368 anion is independent of the one-dimensional chain and does not form any covalent contacts to the cation.
The extended structure forms a chain of K + cations, bridged by 2 -O-dimethylacetamide moieties. The two independent K + cations are located at [0, 0, 0] and [0, 0, 1 2 ] (Wyckoff positions a and b, respectively) and the iodine is located at [ 2 3 , 1 3 , z] (Wyckoff position d). In the primary structure, each K + cation adopts a slightly distorted octahedral coordination sphere (key bond lengths and angles are given in Table 1).

Supramolecular features
The 2 -O-dimethylacetamide bridging the two K + cations forms a linear [K(DMA) 3 ] + chain parallel to the c axis. The application of the 3 symmetry results in an aesthetically pleasing 'snowflake' configuration when viewed along the c axis (Fig. 2). The iodide counter-ion resides in the channels formed by the [K(DMA) 3 ] + chains. With regards to the extended structure, there are very weak C-HÁ Á ÁI interactions within the lattice (Table 2). These serve to locate the iodine in a pocket within the structure. The atom-labeling scheme for KIÁ3DMA, with displacement ellipsoids depicted at the 50% probability level. [Symmetry codes: (i) Àx, Ày, Àz; Legend: black = carbon, dark blue = nitrogen, light blue = potassium, magenta = iodine, and red = oxygen. H atoms have been omitted for clarity.

Table 2
Hydrogen-bond geometry (Å , ).  Batsanov & Struchkov (1994), with a KÁ Á ÁK distance of 3.4170 (10) Å and a K-O distance of 2.6570 (13) Å . In the KIÁ3DMA structure reported herein, the K1Á Á ÁK2 distance is 3.6728 (4) Å , which is longer by approximately 0.106 Å . In the Gonzalez-Rodriguez and Cunningham structures, iodine is found to form bonds to the K + cations, while it is located in a channel within the Batsanov structure and not covalently bound. In the title compound, the iodine is not covalently bonded to the cation chain.
A search in the Cambridge Structure Database for free acetamide returned 180 results, featuring C O bond lengths between 1.123 Å (Patra & Goldberg, 2013)

Synthesis and crystallization
A carbon-carbon Heck coupling reaction catalyzed by a Pd II diphosphane precatalyst was performed using conditions established previously by Brase & de Meijere (1998). In a typical synthesis, 1-iodo-4-nitrobenzene (IC 6 H 4 NO 2 ; 102.1 mg, 0.41 mmol) was mixed with 2 equivalents of n-butyl acrylate [CH 2 CHCOO(CH 2 ) 3 CH 3 ; 105.6 mg, 0.82 mmol] in the presence of K 2 CO 3 (63.6 mg, 0.46 mmol) and n-Bu 4 NBr (13 mg, 0.041 mmol) in dimethylacetamide (DMA) over a period of 4 h at 413 K. The title compound formed and was recrystallized from the filtered reaction mixture at room temperature. The target Pd II complex of the reaction has been reported (Comanescu & Iluc, 2014).