  We show how quasi-one-dimensional correlated insulating states arise at
two-thirds filling in organometallic multinuclear coordination complexes
described by layered decorated honeycomb lattices. The interplay of spin-orbit
coupling and electronic correlations leads to pseudospin-1 moments arranged in
weakly coupled chains with highly anisotropic exchange and a large trigonal
splitting. This leads to a quantum phase transition from a Haldane phase to a
topologically trivial phase as the relative strength of the spin-orbit coupling
increases.
