  This paper reports on an unmodeled, all-sky search for gravitational waves
from merging intermediate mass black hole binaries (IMBHB). The search was
performed on data from the second joint science run of the LIGO and Virgo
detectors (July 2009 - October 2010) and was sensitive to IMBHBs with a range
up to $\sim 200$ Mpc, averaged over the possible sky positions and inclinations
of the binaries with respect to the line of sight. No significant candidate was
found. Upper limits on the coalescence-rate density of nonspinning IMBHBs with
total masses between 100 and $450 \ \mbox{M}_{\odot}$ and mass ratios between
$0.25$ and $1\,$ were placed by combining this analysis with an analogous
search performed on data from the first LIGO-Virgo joint science run (November
2005 - October 2007). The most stringent limit was set for systems consisting
of two $88 \ \mbox{M}_{\odot}$ black holes and is equal to $0.12 \
\mbox{Mpc}^{-3} \ \mbox{Myr}^{-1}$ at the $90\%$ confidence level. This paper
also presents the first estimate, for the case of an unmodeled analysis, of the
impact on the search range of IMBHB spin configurations: the visible volume for
IMBHBs with nonspinning components is roughly doubled for a population of
IMBHBs with spins aligned with the binary's orbital angular momentum and
uniformly distributed in the dimensionless spin parameter up to 0.8, whereas an
analogous population with antialigned spins decreases the visible volume by
$\sim 20\%\,$.
