Triply bonded Nb24+ tetragonal lantern compounds:: Some accompanied by novel B-H•••Na+ interactions

The diniobium tetragonal lantern compound Nb-2(hpp)(4), 1, has been prepared in high yields by the reaction of NbCl3(DME), DME = dimethoxyethane, with a mixture of lithium naphthalenide and Li(hpp), hpp = the anion of 1,3,4,6,7,8-hexahydropyrimido[l,2-a]pyrimidine. Compound 1 interacts with two equivalents of NaEt3BH to give the bis-adduct, 1 . 2NaEt(3)BH. In a refluxing mixture of THF/toluene, 1 . 2NaEt(3)BH loses one NaEt3BH molecule to give 1 NaEt3BH. Both adducts contain short Na to N-C-N "pseudo-allylic" interactions to the coordinated hpp ligand. Very little variation can be seen in the Nb-Nb bond distances, which are 2.2035(9), 2.2064(3), and 2.2187(7) Angstrom for 1, 1 . 2NaEt(3)BH and 1 . NaEt3BH, respectively. By a synthetic route similar to that used to make 1, Nb-2(azin)(4). 2LiCl . 4THF, 2, was prepared using the anion of 7-azaindole; the Cl- ions are loosely coordinated to the Nb atoms. This ligand tends to give long metal-metal distances, and the Nb-Nb distance of 2.278(2) Angstrom is 0.07 Angstrom longer than that in 1.