mer-Hydridotris(trimethylphosphane-κP)(d-valinato-κ2 N,O)iridium hexafluoridophosphate dichloromethane 0.675-solvate

The title compound, [Ir(C5H10NO2)H(C3H9P)3]PF6·0.675CH2Cl2, an iridium compound with a meridional arrangement of PMe3 groups, O,N-bidentate coordination of d-valine and with a hydride ligand trans to the N atom is compared with the l-valine complex reported previously. As expected, the complexes from the corresponding l and d isomers of valine crystallize in enantiomorphic space groups (P43 and P41, respectively). In the crystal, N—H⋯O and N—H⋯F hydrogen bonding is observed, the N—H to carbonyl oxygen hydrogen bond producing a helical motif that proceeds along the 41 screw of the c axis.


Related literature
The structure of the related l-valine complex has been described by Roy et al. (2006). For studies of hydrogenbonded lattice systems that lose crystallinity on loss of solvent and an analogous one that retains crystallinity, see: Parkin & Behrman (2009, 2011). An analysis of the geometric paramaters for hydrogen bonds is given by Wood et al. (2009).

Comment
Both the D-and L-Valine complexes of the type [HIr(AA)(PMe 3 ) 3 ][PF 6 ] crystallize in primitive tetragonal space groups, with the L-valine complex in P4 3 and the D-valine complex in the enantiomorphic group P4 1 . The former structure was measured at room temperature on a Siemens P4 diffractometer while the latter was measured on an Oxford Diffraction instrument at 100 K. Accounting for room temperature vs. 100 K, the unit-cell parameters are essentially the same. Figure   1 shows a thermal ellipsoid plot of the asymmetric unit of the title compound. N-H to carbonyl oxygen hydrogen bonding produces a helical motif that proceeds along the 4 1 screw of the c axis. The helical motif for the H-bonding is shown in figure 2. Hydrogen bonding also occurs between the second N-H atom and a fluorine atom of the PF 6anion. Table 1 lists the hydrogen bonding parameters for the hydrogen bonds N1-H1A···F1 and N1-H1B···O2. With an H···O distance of 2.02 (6) Å and an N-H···O angle of 172 (6)°, the N1-H1B···O bond is a strong hydrogen bond while the N -H···F bond is not as strong based on geometric parameters, but still not a "weak" H-bond (Wood et al., 2009).
In addition to the overall quality improvement of the structure of the D compound reported here at 100 K compared with the L-valine compound at RT, the issue of lattice solvent is an interesting one. In the previous report, the crystals were isolated and handled in air at room temperature for a period of days before mounting them and collecting data at room temperature. The L-valine complex showed very large voids (573 Å 3 ) with negligible residual electron density. The current D-valine complex clearly shows dichloromethane within the structure, but each dichloromethane site is only ~68% occupied. Here, it would appear that dichloromethane of solvation is partially lost.
Often, for molecular compounds, loss of solvent of crystallization results in the collapse of the crystal lattice. The Dvaline complex with partial loss and the L-valine with complete solvent loss maintain the crystal lattice structural integrity. Figure 3 shows a view of both the D-and L-valine space filling packing diagrams that show, the CH 2 Cl 2 in the title compound and the empty space in the L-valine structure reported previously. The loss of solvent with preservation of the crystal lattice is the norm for metal-organic framework (MOF) compounds, but those involve strong coordination bonds between metals and linking ligands. Maintaining the crystal lattice solely with hydrogen bonding is not new, but it is somewhat rare. For another example, see Parkin and Behrman (2011).

Experimental
For a detailed description of the synthetic procedure for all of the tris-trimethylphosphine iridium amino acid complexes, see (Roy et al., 2006). The title compound was recrystallized by the layering of diethyl ether over a dichloromethane solution. After several days of slow diffusion, suitable single crystals grew at the interface.

Refinement
The H-atoms on the amine nitrogen were located from the residual electron density map and the positions refined independently. The N-H bonds are 0.92 (6) and 0.83 (6) Å. The displacement parameters were fixed at U iso (H)=1.2Ueq(N1). The hydride was located in the residual electron density map, the distance restrained to 1.57 (2) Å, and the displacement parameter fixed at U iso (H1)=1.5U eq (Ir1). After locating the iridium hydride salt, additional strong residual electron density peaks were modeled as a partially occupied CH 2 Cl 2 molecule with occupancy that refined to 0.675 (6).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (