Crystal structure of the tetrahydrofuran disolvate of a 94:6 solid solution of [N 2,N 6-bis(di-tert-butylphosphanyl)pyridine-2,6-diamine]dibromidomanganese(II) and its monophosphine oxide analogue

The MnBr2 complex of N 2,N 6-bis(di-tert-butylphosphanyl)pyridine-2,6-diamine (1·MnBr2) co-crystallizes with 5.69% of the monophosphine oxide analogue (1O·MnBr2) and two tetrahydrofuran (THF) molecules, namely {N 2,N 6-bis(di-tert-butylphosphanyl)pyridine-2,6-diamine}dibromidomanganese(II)–[bis(di-tert-butylphosphanyl)({6-[(di-tert-butylphosphanyl)amino]pyridin-2-yl}amino)phosphine oxide]dibromidomanganese(II)–tetrahydrofuran (0.94/0.06/2), [MnBr2(C21H41N3P2)]0.94[MnBr2(C21H41N3OP2)]0.06·2C4H8O. The 1·MnBr2 and 1O·MnBr2 complexes are connected by weak N—H⋯Br hydrogen bonding into chains extending along [001] with the THF molecules located between the layers formed by these chains.


Structural commentary
The title crystal possesses P2 1 /c symmetry. A 94. 31:5.69 (14) overlay of the 1ÁMnBr 2 complex and the corresponding monooxidized 1OÁMnBr 2 complex is located on general positions. Two crystallographically independent THF solvent molecules are likewise located on general positions, one of which is positionally disordered.
The ligands of both the non-oxidized and the oxidized complexes occupy virtually the same space. They could therefore not be resolved into distinct sites and even the atomic displacement parameters (ADPs) are not significantly enlarged. The Mn and Br atoms, on the other hand, are clearly separated within the resolution of the experiment.
The Mn II atom of the non-oxidized 1ÁMnBr 2 complex features fivefold coordination with the PNP-ligand and two bromine atoms (Fig. 1) in a square-pyramidal conformation with a 5 parameter (Addison et al., 1984) of 0.083. The ideal 5 values for square-pyramidal and trigonal-bipyramidal coordinations are 0 and 1, respectively. The Mn atom is nearly equidistant [2.644 (9) and 2.639 (10) Å ] to both P atoms.
In the monooxidized 1OÁMnBr 2 complex (Fig. 2), the coordination deviates more from the square-pyramidal mode than in 1ÁMnBr 2 (5 = 0.196; Fig. 3). The O atom introduces an additional distortion, leading to an increased deviation from planarity, whereby the Mn 0 and O atoms are located on opposite sides of the LS plane described above [0.712 (13) Å

Figure 1
The molecular structure of 1ÁMnBr 2 . C (grey), N (blue), P and Br (orange), and Mn (purple) atoms are represented by ellipsoids drawn at the 50% probability levels. H atoms have been omitted for clarity.

Figure 2
The molecular structure of 1OÁMnBr 2 . Atom colour codes as in Fig. 1 with O (red).

Figure 3
The coordination of the Mn atom in 1OÁMnBr 2 . Atom colour codes as in Figs. 1 and 2.
The amine functionality that is not bonded to THF connects via a weak N2-HÁ Á ÁBr1(Br1 0 ) hydrogen bond, thus forming infinite chains of complex molecules extending along [001]. Adjacent complexes in this chain are related by the c glide reflection.
No further bonding intermolecular interactions are observed in the crystal structure. The chains of complexes contact in the [001] direction via van der Waals interactions, forming distinct layers parallel to (100). Between these layers are located the hydrogen-bonded and free THF molecules (Fig. 5).

Database survey
A search in the Cambridge Structural Database (Version 5.37; last update March 2016; Groom et al., 2016) for structures of fivefold-coordinated Mn/PNP complexes revealed no entries. Nevertheless, our group recently published the MnCl 2 complex of the isopropyl analogue of 1 (see above). Moreover, three related Mn(PNP)(CO) 3 complexes with octahedral coordination modes are known. One of these compounds is likewise pyridine-based (Flö rke & Haupt, 1991), whereas the others are based on ditolylamines (Radosevich et al., 2009). No ligand mono-oxidized analogues of Mn/PNP complexes have been described up to now.

Synthesis and crystallization
The synthesis of 1 was performed as described previously (Deibl & Kempe, 2016). THF was dried over Na under an Ar atmosphere. All other reagents were obtained commercially and used as received. 1 and MnBr 2 were stirred in dry THF for 18 h under an Ar atmosphere (see reaction scheme). The complex 1ÁMnBr 2 was precipitated by addition of n-pentane. The microcrystalline powder was washed twice with npentane. Crystals were grown by slow vapour diffusion of diethyl ether into a room-temperature saturated solution of 1ÁMnBr 2 in THF.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms bonded to C atoms were placed in calculated positions and refined as riding atoms, with fixed bond lengths in the range 0.95-1.00 Å and U iso (H) = 1.2U eq (C) or 1.5U eq (C Me ). The two amine H atoms were located in difference-Fourier maps and were refined freely.
Excessive electron density in difference-Fourier maps was attributed to alternative positions of the Mn and Br atoms. The Mn and Br atoms were therefore refined as positionally  Table 1 Hydrogen-bond geometry (Å , ).

Figure 4
Intermolecular hydrogen bonding (dashed lines) in the title crystal.
Complexes are shown as an overlay of 1ÁMnBr 2 and 1OÁMnBr 2 . Atom colour codes as in Figs. 1 and 2.

Figure 5
Packing plot of the title crystal looking along [010]. disordered (minor positions: Mn 0 and Br 0 ). The occupancies of the atoms of both orientations were constrained to the same value and the sum of the occupancies of both orientations were constrained to 1. The atoms in the minor (ca 6%) orientation were modelled with isotropic ADPs. The minor orientation featured an unreasonably long Mn-P distance (ca 3.18 Å ). Inspection of the electron density in the difference-Fourier map close to the P atom revealed a faint positive peak that was attributed to an O atom that is bound to the P atom, forming an phosphine oxide. The occupancy of this atom was constrained to be equal to the occupancy of the minor positions. The position of the additional O atom was refined freely. A C atom of a THF molecule featured excessively anisotropic ADPs. The position was therefore split and refined as positionally disordered with the sum of the occupancies of both positions constrained to 1; occupancy ratio 0.526 (14):0.474 (14). Both C atoms were refined with isotropic ADPs.  Data collection: APEX2 (Bruker, 2015); cell refinement: SAINT-Plus (Bruker, 2015); data reduction: SAINT-Plus (Bruker, 2015); program(s) used to solve structure: SHELXT (Sheldrick, 2015); program(s) used to refine structure: JANA20006 (Petříček et al., 2014); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: publCIF (Westrip, 2010).