( metal-metal ( bond ; ) )
(ROOT (NP (JJ metal-metal) (NN bond) (: ;)))
metal-metal bond ;
(ROOT (S (NP (DT The) (JJ metallic) (NN bond)) (VP (VBZ is) (ADJP (JJ responsible) (PP (IN for) (NP (NP (DT the) (NNS properties)) (PP (IN of) (NP (NNS metals))))))) (. .)))