Synthesis and properties of isostructural transition-metal (copper, nickel, cobalt, and iron) compounds with 7,7',8,8'-tetracyanoquinodimethanide(1-) in an unusual monodentate coordination mode: crystal structure of bis(3,5-bis(pyridin-2-yl)-4-amino-1,2,4-triazole)bis(7,7',8,8'-tetracyanoquinodimethanido)copper(II)