We present a catalog of 792 DR5 SDSS quasars with optical spectra that have been observed serendipitously in the X-rays with the 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 \geq 2 \sigma account for 87 % of the sample ( 685 quasars ) , and 473 quasars are detected at \geq 6 \sigma , sufficient to allow X-ray spectral fits .
For detected sources , \sim 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 \geq 6 , resulting in a weighted mean photon index \Gamma = 1.91 \pm 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 \pm 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 .