The first member, Y-2(OH)(5.46)(B12H12)(0.23)Cl-0.08: 4.98H(2)O, of a new family of boron -containing substances, closo-dodecaborate intercalated layered rare-earth hydroxides, was synthesized using a microwave -assisted hydrothermal method. The structure and composition of this compound were studied by X-ray diffraction, transmission and scanning electron microscopy, thermal analysis, inductively coupled plasma mass spectrometry, IR spectroscopy, and X-ray photoelectron spectroscopy. The title compound had the composition Y-2(OH)(5.46)(B12H12)(0.23)Cl(0.08.)4.98H(2)O and crystallized in a form of plate-like, aggregated particles less than 10 yttrium hydroxide host layers was demonstrated.