Triply Bonded Nb24+Tetragonal Lantern Compounds: Some Accompanied by Novel B−H···Na+Interactions
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Abstract
The diniobium tetragonal lantern compound Nb2(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[1,2-a]pyrimidine. Compound 1 interacts with two equivalents of NaEt3BH to give the bis-adduct, 1·2NaEt3BH. In a refluxing mixture of THF/toluene, 1·2NaEt3BH 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) Å for 1, 1·2NaEt3BH and 1·NaEt3BH, respectively. By a synthetic route similar to that used to make 1, Nb2(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) Å is 0.07 Å longer than that in 1.
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