Coordination chemistry effects of the space-demanding solvent molecule N,N′-dimethylpropyleneurea

Crystallographic investigations of eight homoleptic N,N′-dimethylpropyleneurea (dmpu) coordinated metal ions in the solid state, [Mg(dmpu)5]I2 (1), [Ca(dmpu)6]I2 (2), [Ca(dmpu)6](ClO4)2 (3), [Ca(dmpu)6](CF3SO3)2 (4), [Sr(dmpu)6](CF3SO3)2 (5), [Ba(dmpu)6](CF3SO3)2 (6), [Sc(dmpu)6]I3 (7), and [Pr(dmpu)6]I(I3)2 (8), and the complex [CoBr2(dmpu)2] (9) as well as the structures of the dmpu coordinated calcium, strontium, barium, scandium(iii) and cobalt(ii) ions and the cobalt(ii) bromide complex in dmpu solution as determined by EXAFS are reported. The methyl groups in the dmpu molecule are close to the oxygen donor atom, causing steric restrictions, and making dmpu space-demanding at coordination to metal ions. The large volume required by the dmpu ligand at coordination contributes to crowdedness around the metal ion with often lower coordination numbers than for oxygen donor ligands without such steric restrictions. The crowdedness is seen in M⋯H distances equal to or close to the sum of the van der Waals radii. To counteract the space-demand at coordination, the dmpu molecule has an unusual ability to increase the M–O–C bond angle to facilitate as large coordination numbers as possible. M–O–C bond angles in the range of 125–170° are reported depending on the crowdedness caused by the coordination figure and the M–O bond distance. All reported structures of dmpu coordinated metal ions in both the solid state and dmpu solution are summarized to study the relationship between the M–O–C bond angle and the crowdedness around the metal ion. However, highly symmetric complexes seem to be favoured in the solid state due to favourable lattice energies. As a result, the dmpu coordinated lanthanoid(iii) ions are octahedral in the solid state, while they, except lutetium, are seven-coordinate in the dmpu solution.

Repeated tests using the same mounting method of structurally similar lanthanum(III) and neodymium(III) compounds resulted in break down of the crystals without formation of new compounds.
The partial oxidation of iodide ions may be caused by either oxygen gas in air being reduced (to hydroxide ions) or by removed non-coordinated dmpu molecules to unknown compounds.We are unable to present chemical proof for either of these reaction pathways, as no chemical analysis was performed on the remaining liquid.

EXAFS experiments
The calcium, scandium and cobalt K-edge and barium L 3 -edge EXAFS spectra of dmpu solutions of trifluoromethanesulfonate salts were performed at the wiggler beam line 4-1 (old station) at Stanford Synchrotron Radiation Lightsource (SSRL), USA, which was operated at 3.0 GeV and a maximum current of 100 mA.The EXAFS station was equipped with a Si [111] double-crystal monochromator and higher-order harmonics were reduced by detuning the second monochromator crystal to reflect 30% of maximum intensity for the calcium, scandium, and barium data at the end of the scans.Internal energy calibration was made with scandium, calcium, or barium metal foils when the intensity of the beam was sufficient at the metal foil between the second and third ion chamber, otherwise, edge spectra of the metal foil were recorded before and after each EXAFS experiment.The first inflection point of the rising edge of the metal was assigned to 4038.5, 4492, 7709.5, and 5247 eV for calcium, scandium, cobalt, and barium, respectively. 1The experiments were performed in fluorescence mode for calcium, scandium, and barium in a helium atmosphere using a Lytle detector without an X-ray filter and with a very gentle flow of nitrogen gas at ambient temperature.The strontium data were collected at beam-line I811 at MAX-lab, Lund University, in transmission mode with stationary gas mixtures in the ion chambers.The EXAFS station was equipped with a Si[200] doublecrystal monochromator and higher-order harmonics were reduced by detuning the second monochromator crystal to reflect 60%.The inflection point on the absorption of metallic strontium was assigned to 16105 eV. 1 For each sample 3-4 scans were averaged giving satisfactory data quality up to k = 13 Å -1 (k 3 -weighted data).The treatment of the EXAFS data was carried out by means of the EXAFSPAK program package 2 using standard procedures for pre-edge subtraction and spline removal.Calculated model functions using ab initio calculated Selected bond distances and angles are given in Table 1.The packing structure of 3 is shown in Fig. S1.
Selected bond distances and angles are given in Table 1.The packing structure of 4 is shown in Fig. S2.

Further information about compounds 2 and 4
Compound 2 ([Ca(dmpu) 6 ]I 2 ): We cannot adjust the low value of max (sin theta)/λ.The data were collected for several years ago and the raw data as well as the crystal has disappeared.
However, even with a new data collection we feel that the structure would not change a measurable way.
Compound 4 ([Ca(dmpu) 6 ](CF 3 SO 3 ) 2 ): The large shift/esd was due to an exti parameter with vanishing value.When it was removed the refinement became stable.We cannot re-establish the transmission factors since this is very old data and the original frames is not available anymore.It is the same with the large Hirshfeld difference alert A that we cannot explain.
Perhaps that is a deficit in the treatment of the original raw data.This structure is generally of quite low accuracy.

Figure S6a .
Figure S6a.Packing structure of [Pr(dmpu) 6 ] 3+ with a mix of iodide ions and triiodide ions viewed along the trigonal axis (c axis).The atoms are shown with 50% probability ellipsoids except the iodine atoms that are shown as spheres.

Figure S6b .
Figure S6b.Stereo view of the local structure of the [Pr(dmpu) 6 ] 3+ complexes with an iodide ion on the threefold axis at the origin and also the triiodide ions on the six equivalent threefold axes around the Pr(dmpu) 6 3+ -iodide chain.The atoms are shown with 50% probability ellipsoids except for the iodine atoms that are shown as spheres.

Table S1 .
Overview of distances; Å, in N,N'-dimethylpropylene urea solvated metal ions in solution and solid state, d(M-O) dmpu , and the M-O bond distances in the corresponding hydrated metal ions in aqueous solution, d(M-O) aq .For references to the values in water, see Table1.
a b R. S. Rowland and R. Taylor, Intermolecular Nonbonded Contact Distances in Organic Crystal Structures: Comparison with Distances Expected from van der Waals Radii.J. Phys.Chem.1996, 100, 7384-7391.