[NaCl][Cu(HSeO₃)₂], NaCl-intercalated Cu(HSeO₃)₂: synthesis, crystal structure and comparison with related compounds

Single crystals of [NaCl][Cu(HSeO 3 ) 2 ] have been prepared by the chemical vapor transport reactions. Its crystal structure (monoclinic, C 2/ c , a = 13.9874(7), b = 7.2594(4), c = 9.0421(5) Å, β = 127.046(2)°, V = 732.81(7) Å 3 ) is based upon electroneutral [Cu(HSeO 3 ) 2 ] sheets formed by corner sharing between the [CuO 4 ] squares and (HSeO 3 ) groups that are parallel to the (100) plane. Each (SeO 2 OH) – group forms the O h 1 ... O2 hydrogen bond to an adjacent hydroselenite group to constitute a [(SeO 2 OH) 2 ] 2– dimer that provides additional stabilization of the copper diselenite sheet. The [Cu(HSeO 3 ) 2 ] sheets alternate with the sheets consisting of zigzag–Na–Cl–Na–Cl–chains formed by Cl atoms and disordered Na sites. The chains are parallel to the c axis. The linkage between the alternating electroneutral [Cu(HSeO 3 ) 2 ] and [NaCl] sheets is provided by the Cu–Cl and Na–O bonds. The coordination of Na is fivefold and consists of three O and two Cl atoms. [NaCl][Cu(HSeO 3 ) 2 ] is a new member of the group of compounds based upon the M(HSeO 3 ) 2 layers (M 2+ = Cu, Co, Cd). The prototype structure for this group is [Cu(HSeO 3 ) 2 ] that does not have any chemical species separating the copper hydroselenite layers. In other compounds, the interlayer space between the [Cu(HSeO 3 ) 2 ] 0 layers is occupied by structural units of different complexity. [NaCl][Cu(HSeO 3 ) 2 ] can be considered as [Cu(HSeO 3 ) 2 ] intercalated with the NaCl layers consisting of one-dimensional–Na–Cl–Na–Cl–chains.