Synthesis of novel quadruply bridged M 2 Se 4 clusters trans/anti and trans/syn-[(η 5 -RC 5 H 4 ) 2 M 2 (μ-Se) 2 (μ-SeCH 2 Ph) 2 ] (M=Mo, W) via an unexpected reaction of M≡M triply bonded complexes [(η 5 -RC 5 H 4 ) 2 M 2 (CO) 4 ] with dibenzyl diselenide. Crystal structures of a pair of isomers trans/anti- and trans/syn-[(η 5 -EtO 2 CC 5 H 4 ) 2 Mo 2 (μ-Se) 2 (μ-SeCH 2 Ph) 2 ]