A building block approach has been used to prepare a new family of hexanuclear magnetic molecules Mn4Nb2, Fe4Nb2, and Co4Nb2 of general formula [M-II(tmphen)(2)](4)[Nb-IV(CN)(8)](2)}center dot solv (M = Mn, Fe, Co; tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline; solv = MeOH and/or H2O). Mn4Nb2 exhibits a magnetocaloric effect at temperatures close to 1.8 K, and Fe4Nb2 undergoes an incomplete gradual spin crossover and a photomagnetic response related to light-induced excited spin state trapping.