Tetraaza macrocyclic metal complexes containing a medium-sized chelate ring. 2. X-ray structural studies of trans-dichloro(1,4,7,10-tetraazacyclotetradecane)nickel(II) hydrate, (1,4,7,10-tetraazacyclopentadecane)nickel(II) perchlorate, and trans-dichloro(1,4,7,10-tetraazacyclohexadecane)nickel(II)