Combination Chemistry of Hexa-Copper-Substituted Polyoxometalates Driven by the Cu^II−Polyhedra Distortion: From Tetramer, 1D Chain to 3D Framework

Reaction of CuCl2·2H2O and trivacant Keggin polyoxoanion Na9[A-α-PW9O34]·7H2O in the presence of ethylene-diamine/1,2-diaminopropane (en/enMe) under hydrothermal conditions led to five novel inorganic−organic hybrid polyoxotungstates (POTs):[Cu(en)2]2[Cu(en)2(H2O)]2[Cu(H2O)2][Cu4(H2O)2(B-α-PW9O34)2]·2H2O(1), [Cu6(μ3−OH)3(en)3(H2O)5(B-α-PW9O34)]·6H2O (2), Na6{[Cu6(μ3−OH)3(en)3(H2O)2(B-α-PW9O34)]2[Cu4(H2O)2(B-α-PW9O34)2]}·2 H2en·8H2O (3), [Cu6(μ3−OH)3(en)3(H2O)3(B-α-PW9O34)]·4H2O (4), [CuII6CuI4(μ6-O)(OH)18][Cu6(μ3−OH)3(enMe)3(H2O)3(B-α-PW9O34)]4·4H3O·2H2O (5). 1 is a new 1D chain constructed from alternate tetra-CuII sandwiched units [CuII4(H2O)2(B-α-PW9O34)2]10− and dinuclear [CuII2(H2O)6]4+ units. 2−5 are a series of novel transition-metal substituted polyoxometalates (TMSPs) comprising hexa-CuII substituted {Cu6PW9} units (Cu6=Cu6(μ3−OH)3, PW9=B-α-PW9O34, Scheme 1). 2 is an unusual monomer. 3 is an unprecedented tetramer built by two types of TMSP units, [Cu6PW9(en)3(H2O)2] and [CuII4(H2O)2(PW9)2]10−. 4 is a novel chain assembled from [Cu6PW9(en)3(H2O)3] units by double-bridging mode. Most interestingly, 5 is a open framework made by [Cu6PW9(enMe)3(H2O)3] units, in which the novel decacopper oxygen clusters, [CuI4CuII6(μ6-O)(OH)18]4− formed in situ, are encapsulated into the channels, and 5 represents the first decametallic-cluster-containing open framework built by TMSP units. 2−5 all contain the hexa-CuII substituted POT unit {Cu6PW9L3(H2O)n} (L = en/enMe, n < 6) made by {Cu6L3(H2O)n} core and trivacant Keggin PW9 fragments. Moreover, 3−5 can be viewed as combining derivatives of 2 through substituting water ligands on hexa-CuII {Cu6L3(H2O)n} units by terminal oxygen atoms of PW9 units. Importantly, the CuII-polyhedra Jahn−Tell/pseudo-Jahn−Teller distortion plays a crucial role in the formation of 1−5. The magnetic behaviors of 2−5 show antiferromagnetic interactions between the CuII ions in the hexa-CuII cluster.