  We present a catalog of 792 DR5 SDSS quasars with optical spectra that have
been observed serendipitously in the X-rays with the \emph{XMM-Newton}. These
quasars cover a redshift range of z = 0.11 - 5.41 and a magnitude range of i =
15.3-20.7. Substantial numbers of radio-loud (70) and broad absorption line
(51) quasars exist within this sample. Significant X-ray detections at >2sigma
account for 87% of the sample (685 quasars), and 473 quasars are detected at
>6sigma, sufficient to allow X-ray spectral fits. For detected sources, ~ 60%
have X-ray fluxes between F(2-10 keV) = 1 - 10 x 10^-14 ergs cm^-2 s^-1. We fit
a single power-law, a fixed power-law with intrinsic absorption left free to
vary, and an absorbed power-law model to all quasars with X-ray S/N > 6,
resulting in a weighted mean photon index Gamma = 1.91 +/- 0.08, with an
intrinsic dispersion sigma_Gamma = 0.38. For the 55 sources (11.6%) that prefer
intrinsic absorption, we find a weighted mean N_H = 1.5 +/- 0.3 x 10^21 cm^-2.
We find that Gamma correlates significantly with optical color, Delta(g-i), the
optical-to-X-ray spectral index (alpha_ox) and the X-ray luminosity. While the
first two correlations can be explained as artefacts of undetected intrinsic
absorption, the correlation between Gamma and X-ray luminosity appears to be a
real physical correlation, indicating a pivot in the X-ray slope.
