A new "active" chromium(III) hydroxide: Cr2(.mu.-OH)2(OH)4(OH2)4.2H2O. Characterization and use in the preparation of salts of the (H2O)4Cr(.mu.-OH)2Cr(OH2)44+ ion. Crystal structure of [(H2O)4Cr(.mu.-OH)2Cr(OH2)4][(H3C)3C6H2SO3]4.4H2O