Triclinic La 7 Zn 2 P 11 with P 3- , P 2 4- , and P 3 5- units: a combined study by 31 P solid-state NMR spectroscopy and single crystal X-ray diffraction.

The ternary polyphosphide La 7 Zn 2 P 11 was synthesized from the elements by using a salt flux or via a ceramic method in sealed quartz ampoules. The obtained samples were investigated by X-ray powder and single crystal diffraction: own type, P 1̄, a = 775.33(13), b = 827.45(13), c = 1502.8(3) pm, α = 82.111(3), β = 77.034(3), γ = 89.996(3)°, w R 2 = 0.1553, 5852 F 2 values and 183 variables. This peculiar structure is characterized by the simultaneous presence of three distinct anionic phosphide species, namely P 3- , P 2 4- , and P 3 5- units. La 7 Zn 2 P 11 is an electron precise Zintl phase: (7La 3+ ) 21+ (2Zn 2+ ) 4+ (4P 3- ) 12- (2P 2 4- ) 8- (P 3 5- ). The P-P single bond distances range from 219.2 to 223.0 pm. The zinc sites show tetrahedral phosphorus coordination by three P 3- and one P 2 4- species. The tetrahedra are condensed to chains via common corners. The P 3 5- units with P-P-P angles of 113.7° have exclusively lanthanum coordination. 31 P solid-state NMR was used to probe the phosphorus local environments, connectivities and spatial proximities. The eleven crystallographically distinct phosphorus atoms were assigned with the help of two-dimensional homonuclear dipolar correlation experiments. Even though the application of 2D measurements on such phosphorus-based polyanionic compounds is exceedingly challenging because of the wide dispersion of chemical shifts, the fast irreversible decay of the transverse magnetization, and slow spin-lattice relaxation, a complete assignment is possible using radiofrequency-driven dipolar recoupling (RFDR), J -RESOLVED and total-through-bond correlation with R-sequence (R-TOBSY) techniques.