Syntheses, Structures, and Electroluminescence of New Blue/Green Luminescent Chelate Compounds: Zn(2-py-in)2(THF), BPh2(2-py-in), Be(2-py-in)2, and BPh2(2-py-aza) [2-py-in = 2-(2-pyridyl)indole; 2-py-aza = 2-(2-pyridyl)-7-azaindole]