Functionalized Adamantane Tectons Used in the Design of Mixed-Ligand Copper(II) 1,2,4-Triazolyl/Carboxylate Metal–Organic Frameworks

Bistriazoles, 1,3-bis­(1,2,4-triazol-4-yl)­propane (tr2pr) and 1,3-bis­(1,2,4-triazol-4-yl)­adamantane
(tr2ad), were examined
in combination with the rigid tetratopic 1,3,5,7-adamantanetetracarboxylic
acid (H4-adtc) platform
for the construction of neutral heteroleptic copper­(II) metal–organic
frameworks. Two coordination polymers, [{Cu4(OH)2(H2O)2}­{Cu4(OH)2}­(tr2pr)2(H-adtc)4]·2H2O (1)
and [Cu4(OH)2(tr2ad)2(H-adtc)2(H2O)2]·3H2O (2), were synthesized and structurally characterized. In complexes 1 and 2, the N1,N2-1,2,4-triazolyl (tr) and μ3-OH– groups serve as complementary bridges between
adjacent metal centers supporting the tetranuclear dihydroxo clusters.
The structure of 1 represents a unique association of
two different kinds of centrosymmetrical {Cu4(OH)2} units in a tight 3D framework, while in compound 2, another configuration type of acentric tetranuclear metal clusters
is organized in a layered 3,6-hexagonal motif. In both cases, the
{Cu4(OH)2} secondary building block and trideprotonated
carboxylate H-adtc3– can
be viewed as covalently bound six- and three-connected nodes that
define the net topology. The tr ligands, showing μ3- or μ4-binding patterns, introduce additional integrating
links between the neighboring {Cu4(OH)2} fragments.
A variable-temperature magnetic susceptibility study of 2 demonstrates strong antiferromagnetic intracluster coupling (J1 = −109 cm–1 and J2 = −21 cm–1), which
combines for the bulk phase with a weak antiferromagnetic intercluster
interaction (zj = −2.5 cm–1).