  We compile a sample of X-ray-selected galaxy groups and clusters from the
XMM-Newton serendipitous source catalogue (2XMMi-DR3) with optical confirmation
and redshift measurement from the Sloan Digital Sky Survey (SDSS). The X-ray
cluster candidates were selected from the 2XMMi-DR3 catalogue in the footprint
of the SDSS-DR7. We developed a finding algorithm to search for overdensities
of galaxies at the positions of the X-ray cluster candidates in the photometric
redshift space and to measure the redshifts of the clusters from the SDSS data.
The detection algorithm provides the photometric redshift of 530 galaxy
clusters. Of these, 310 clusters have a spectroscopic redshift for at least one
member galaxy. About 75 percent of the optically confirmed cluster sample are
newly discovered X-ray clusters. Moreover, 301 systems are known as optically
selected clusters in the literature while the remainder are new discoveries in
X-ray and optical bands. The optically confirmed cluster sample spans a wide
redshift range 0.03-0.70 (median z=0.32). In this paper, we present the
catalogue of X-ray-selected galaxy groups and clusters from the 2XMMi/SDSS
galaxy cluster survey. The catalogue has two subsamples: (i) a cluster sample
comprising 345 objects with their X-ray spectroscopic temperature and flux from
the spectral fitting, and (ii) a cluster sample consisting of 185 systems with
their X-ray flux from the 2XMMi-DR3 catalogue, because their X-ray data are
insufficient for spectral fitting. The updated L_X-T relation of the current
sample with X-ray spectroscopic parameters is presented. We see no evidence for
evolution in the slope and intrinsic scatter of the L_X-T relation with
redshift when excluding the low-luminosity groups.
