  We demonstrate optical spin polarization of the neutrally-charged
silicon-vacancy defect in diamond ($\mathrm{SiV^{0}}$), an $S=1$ defect which
emits with a zero-phonon line at 946 nm. The spin polarization is found to be
most efficient under resonant excitation, but non-zero at below-resonant
energies. We measure an ensemble spin coherence time $T_2>100~\mathrm{\mu s}$
at low-temperature, and a spin relaxation limit of $T_1>25~\mathrm{s}$. Optical
spin state initialization around 946 nm allows independent initialization of
$\mathrm{SiV^{0}}$ and $\mathrm{NV^{-}}$ within the same optically-addressed
volume, and $\mathrm{SiV^{0}}$ emits within the telecoms downconversion band to
1550 nm: when combined with its high Debye-Waller factor, our initial results
suggest that $\mathrm{SiV^{0}}$ is a promising candidate for a long-range
quantum communication technology.
