Syntheses, magnetic properties, and crystal structures of the dimers [LNi(µ-N3)3NiL](ClO4) and [L′2Ni2(N3)2(µ-N3)2](L =N,N′,N″-trimethyl-1,4,7-triazacyclononane; L′= 1,5,9-triazacyclododecane); µ-triazido-vs. µ-diazido-bridging