The following experimental details are with respect to data acquired at B0 = 9.4 T with the 4.0 mm HXY NMR probe (i.e., 1 H-29 Si, Si- Cl, and static Cl experiments). 1 H p/2 and p pulses were 2.5 and 5.0 µs in duration, respectively, corresponding to a 100 kHz radio frequency (RF) field. Si p/2 and p pulses were either ( 1 H- Si experiments) 5 and 10 µs or ( 29 Si-35 Cl) 7 and 14 µs in duration, respectively, corresponding to 50 or 35.7 kHz RF field, respectively. The S3 Cl RF field was calibrated using the previous described heteronuclear Bloch-Siegert shift method with adamantane as the sample. Cl PM saturation pulse with a ca. 16.5 kHz RF field. The 29 Si{ 35 Cl} PM-RESPDOR experiments were recorded with a Cl transmitter offset of ca. -1 MHz. Resonance-Echo DOuble-Resonance (REDOR) dipolar recoupling was applied to the Si spins with a ca. 35.7 kHz RF field (14 µs p pulse) to reintroduce the Si- Cl dipolar interaction under MAS. 1 H→ 29 Si CP was performed at the beginning of the experiment to increase overall sensitivity. All directly detected Si NMR spectra (except for the Si spin echo spectra) were recorded with Car-Purcell-Meiboom-Gill (CPMG) detection to increase sensitivity. 8 100 kHz 1 H RF field of SPINAL-64 decoupling was performed throughout the entire 29 Si{ 35 Cl} PM-RESPDOR experiment and during the acquisition of all Si spectra. 9 Static 35 Cl WURST-CPMG experiments were performed with WURST pulses that were 50 µs in duration and with a sweep width of 800 kHz. Each echo in the CPMG train was 90 µs in duration. A total of 100 echoes were acquired. 50 kHz 1 H RF field of SPINAL-64 decoupling was performed throughout the entire static experiments. 9 1 H{ 35 Cl} DE-RESPDOR spectra of transplatin were recorded with the 1.3 mm HX NMR probe and a 50 kHz MAS frequency. The 1 H T1 of transplatin was ca. 17 s; all experiments utilized a 5 s recycle delay. 1 H{ 35 Cl} DE-RESPDOR experiments were performed with Cl saturation pulses that were 80 µs (4 × trot) in duration with a 80 kHz RF field. The 𝑆𝑅4 ! " heteronuclear dipolar recoupling sequence was applied to the 1 H spins to re-introduce the 1 H- projector-augmented eave (GIPAW) approach. The atomic coordinates and unit cell parameters of the Si-NS models were geometry optimized using the BFGS geometry optimization method and converged to a maximum displacement threshold of 5.0×10 -4 Å, an energy threshold of 5.0×10 -6 eV/atom, a maximum force threshold of 0.01 eV/Å and a maximum stress threshold of 0.02 GPa. Geometry optimization and NMR calculations utilized the Generalized Gradient Approximation (GGA) with the Perdew-Burke Ernzerhof (PBE) exchange-correlation functional, Tkatchenko-Scheffler dispersion corrections, On-the-Fly ultrasoft pseudopotentials (default settings as implemented in CASTEP version 2017 T2), zerothorder regular approximation relativist treatments, and a 630 eV kinetic energy cutoff. A 0.03 and 0.07 Å -1 k-point spacing was used for the NMR (with an energy calculation) and geometry optimization calculations, respectively. Si isotropic shieldings (siso) were converted to isotropic shifts (diso) via a previously published calibration curve using identical calculation parameters. The electronic band structures, total densities of state (DOS), projected DOS and optical absorptions were calculated on the geometry-optimized structures. The primitive cell was utilized for the 0 and 100 % Cl-terminated models. The full cell was utilized for the 20 and 50 %