Crystal structures of 1-(4-chlorophenyl)-2-(diphenylphosphoryl)ethan-1-one and 1-(diphenylphosphoryl)-3,3-dimethylbutan-2-one

The title compounds were synthesized via an Arbuzov reaction between an α-bromoketone and isopropoxydiphenylphosphane. In the crystals of both compounds, molecules are linked via bifurcated C—H⋯(O,O) hydrogen bonds, forming chains propagating along [100] and along [010].


Chemical context
The luminescent properties of lanthanide metals continue to gain attention from researchers interested in the coordination chemistry of f-block elements. Direct excitation of lanthanides is difficult due to the parity forbidden f-f transitions required and relatively low molar absorptivities, but fortunately this excitation can be sensitized with an appropriate organic ligand. The ligand acts as an antenna by harvesting the excitation energy and transferring this energy to the metal emitting state (Weissman, 1942). The resulting emission bands have peak widths less than 10 nm, with a color characteristic of each lanthanide ion. As such, lanthanide metals have found uses in both material and biological applications (de Bettencourt-Dias, 2007;Thibon & Pierre, 2009;Eliseeva & Bü nzli, 2010).
Recently, the carbamoylmethylphosphane oxide (CMPO) group has been shown to be an effective ligand for the sensitization of lanthanide luminescence (Sharova et al., 2012;Rosario-Amorin et al., 2013;Sartain et al., 2015). We undertook this work to investigate the role of the aryl carbonyl group on the ability of the CMPO moiety to act as an antenna in this process. Tuning the structure of these organic ligands may be tantamount to potential improvements in the absorption, transfer, and emission of energy by the resultant lanthanide-ligand complex. We report herein on the synthesis and crystal structure of two new CMPO ligands. ISSN 2056-9890

Structural commentary
The molecular structures of compounds (I) and (II) are shown in Figs. 1 and 2, respectively. While compound (I) crystallized in the orthorhombic centrosymmetric space group Pbca, compound (II) crystallized in the chiral monoclinic space group P2 1 . In compound (I), the two phenyl rings (C9-C14 and C15-C20) are inclined to one another by 75.53 (8) , and to the chlorobenzene ring (C3-C8) by 47.98 (8) and 62.16 (8) , respectively. Atom P1 has a distorted tetrahedral geometry with the C-P O bond angles varying from 112.02 (7) to 114.35 (7) , while the C-P-C angles vary from 105.04 (7) to 106.60 (7) . The carbonyl group (C1 O1) and the phosphoryl group (P1 O2) are anti to one another, most probably to minimize unfavourable dipole-dipole interactions. In compound (II), the two phenyl rings (C7-C12 and C13-C18) are inclined to one another by 86.4 (2) . Atom P1 also has a distorted tetrahedral geometry with the C-P O bond angles varying from 111.47 (16) to 115.06 (16) , while the C-P-C bond angles vary from 101.84 (15) to 109.21 (16) . Here the carbonyl group (C1 O1) and the phosphoryl group (P1 O2) are syn to one another.

Supramolecular features
In the crystal of (I), the phosphoryl groups are aligned with the a axis, and as the individual molecules stack in this direction they appear to rotate around the chlorine atom that lies close to the twofold screw axis, creating a pinwheel arrangement of molecules (Fig. 3) Compound (II) packs in a similar arrangement to (I) in the solid state, although subtle differences result in the formation of a chiral crystal from an achiral compound (Fig. 4). For compound (II), the phosphoryl groups are again aligned in one direction (along the b axis), but in this case, the P1-C2 bond in the center of the molecule lies about a twofold screw axis and acts as the pivot point for the pinwheel arrangement rather than the terminal chlorine atom as seen in the crystal of 524 A view of the molecular structure of compound (I), showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been omitted for clarity.

Figure 2
A view of the molecular structure of compound (II), showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been omitted for clarity. Table 1 Hydrogen-bond geometry (Å , ) for (I).

Database Survey
The The crystal packing diagram of compound (II) (drawn as purple and pink sticks) viewed along: (a) the b axis (the center of the P1-C1 bond that coincides with the twofold screw axis is denoted with a grey dot); (b) the a axis; (c) along the b axis with the bifurcated hydrogen bonds shown as dashed lines (see Table 2 for details). H atoms have been omitted for clarity in parts (a) and (b) and only those involved in hydrogen bonding are shown in (c).

Figure 3
The crystal packing diagram of compound (I) (drawn as blue and orange sticks) viewed along: (a) the a axis (the Cl atoms are shown as dark grey dots); (b) the c axis; (c) along the b axis, with the bifurcated hydrogen bonds shown as dashed lines (see Table 1 for details). H atoms have been omitted for clarity in parts (a) and (b) and only those involved in hydrogen bonding are shown in part (c).
inclined to one another by ca 67.97, 73.25 and 68.24 , respectively, similar to the arrangement in compound (I).

Synthesis and crystallization
The title compounds, (I) and (II), were prepared following slightly modified literature procedures (Arnaud-Neu et al., 1996;Schuster et al., 2009) by the Arbuzov reaction of isopropoxydiphenylphosphane (Shintou et al., 2003) with 2-bromo-4 0 -chloroacetophenone for (I) and 1-bromopinacolone for (II). For both compounds, crystals suitable for X-ray diffraction analysis were grown by slow evaporation of a solution of the compound in CDCl 3 .

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The hydrogen atoms were placed in calculated positions and refined as riding atoms: C-H = 0.95-0.99 Å with U iso (H)= 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for other H atoms.