From a solution prepared by a reaction of Mo 2 (O 2 CCH 3 ) 4 with KTp* (Tp*= hydridotris(3,5-dimethylpyrazolyl)borate, HB(Me 2 Pz) 3 ), in diglyme at room temperature followed by addition of excess (CH 3 ) 3 SiBr to the red solution in refluxing THF, the complexes [HB(Me 2 Pz) 3 )BH][Br 3 Mo(m-Br) 3 MoTp*] (1), Mo 4 (m 3 -O) 2 (m 2 -O) 2 (m 2 -OH) 2 (O) 4 (Me 2 PzH) 6 4 (Me 2 PzH 2 ) 2 (2) and MoBr 2 Tp*(Me 2 PzH) (3), were obtained. Their structures have been determined by X-ray crystallography. The anion of complex 1 consists of two octahedra sharing a common triangular face so those three Br atoms bridge the Mo atoms. The metal centers are also chelated by a tridentate Tp* ligand and coordinated by three Br atoms. Structural comparison of 1 and [HB(Me 2 Pz) 3 )BH][Br 3 Mo(m-Br) 2 (m-H)MoTp*] shows that replacement of the bridging hydride atom by the bromide atom led to the lengthening of the Mo-Mo bond distance by about 0.36 A , . In complex 2, the four octahedra are bridged together through edges. The two molybdenum atoms in the asymmetric unit have different environments although both are formally seven-coordinated. The average oxidation state of molybdenum is + 5, and the four electrons available for Mo-Mo bonding form two localized Mo-Mo single bonds. Complex 2 can be classified into the structural type Mo 4 X a Y b Z c , in which a+b+c= 16. The formation of the cation, [HB(Me 2 Pz) 3 )BH] + , 2 and 3 shows the ready cleavage of the B -N bond of the Tp* ligand.