Copper(I) complexes with distorted tetrahedral environments have been studied as catalytic active sites in electron-transfer reactions and are found in a number of proteins that contain copper (Vallee & Williams, 1968;Colman et al., 1978;Adman et al., 1978). The realization of significantly distorted tetrahedral geometry requires sufficient steric hindrance between the ligands. The methyl groups of the 6,6 0 -dimethyl-2,2 0bipyridyl (C 12 H 12 N 2 ; dmbpy) ligand create a large steric hindrance upon coordination, and, consequently, a common strategy to form distorted tetrahedral complexes is to use dmbpy or its derivatives as ligands (McKenzie et al., 1971;Burke et al., 1980). Previously, compounds with distorted tetrahedral [Cu(dmbpy) 2 ] + cations have been reported, namely [Cu(dmbpy) 2 ]X (X = [BF 4 ] À , [ClO 4 ] À , [PF 6 ] À ), [Cu(dmbpy) 2 ][C 16 H 9 O 8 ]ÁH 2 O (C 16 H 9 O 8 = 2 0 ,3,3 0 -tricarboxybiphenyl-2-carboxylate) and [Cu(dmbpy) 2 ]X 2 (X = [BF 4 ] À , [ClO 4 ] À ). (Burke et al., 1980;Cui et al., 2005;Itoh et al., 2005;Mei et al., 2011;Bozic-Weber et al., 2012;Li et al., 2017) Here, we report two structures with [MF 6 ] 2À (M = Zr, Hf), which are the first known distorted tetrahedral copper compounds with bivalent anions.
ISSN 2056-9890 electronic reprint
Compound (I) has the formula [Cu(dmbpy) 2 ] 2 [ZrF 6 ]Á-1.134H 2 O and crystallizes in the triclinic space group P1 (Fig. 1). The structure of compound (I) features isolated tetrahedral [Cu(dmbpy) 2 ] + cations and octahedral ZrF 6 2À anions (Zr site symmetry 1). The coordination geometry of Cu1 and its donor N atoms deviates from an ideal tetrahedron, as demonstrated by the 83.33 (10) angle between the least squares planes containing Cu1 and each ligand (Table 1). To quantify the deviation from T d symmetry in [Cu(dmbpy) 2 ] + cations, the 4 ' parameter is employed and it gives a value of 0.66 for compound (I) (Okuniewski et al., 2015). The distorted tetrahedral geometry of [Cu(dmbpy) 2 ] + in compound (I) is consistent with other reported compounds containing [Cu(dmbpy) 2 ] + cations (Burke et al., 1980;Cui et al., 2005;Mei et al., 2011;Bozic-Weber et al., 2012). Moreover, the dmbpy ligands in (I) are non-planar and are slightly twisted on the 2,2 0 carbon bond to give a dihedral angle of 8.68 (10) between the N1/C1-C5 and N2/C6-C10 rings and 7. 44 (11) between the N3/C13-C17 and N4/C18-C22 rings. The distorted tetrahedral environment and non-planar ligand geometry give the [Cu(dmbpy) 2 ] + cations a C 2 symmetry, and enantiomeric Áand Ã- [Cu(dmbpy) 2 ] + pairs are related across inversion centers. The octahedral coordination environment of Zr1 is slightly distorted, with Zr1-F bond lengths ranging from 1.9955 (13) to 2.0183 (12) A ˚(Table 1). The minor distortion of the ZrF 6 2À anion may arise due to hydrogen-bonding interactions between water molecules of crystallization and fluorine atoms on the trans position of the ZrF 6
2À anions [see O1-H1BÁ Á ÁF2 (Table 2) The molecular structure of (II) showing 50% displacement ellipsoids. Symmetry code: (i) (i) Àx, 2 À y, 2 À z.
The molecular structure of (I) showing 50% displacement ellipsoids. Symmetry code: (i) Àx, 2 À y, 2 À z.
Hydrogen-bond geometry (A ˚, ) for (I). Compound (II) has the formula [Cu(dmbpy) 2 ] 2 [HfF 6 ]Á-0.671H 2 O and crystallizes in the triclinic space group P1 (Fig. 2). Compound (II) is isostructural to compound (I), therefore, the [Cu(dmbpy) 2 ] + cations also have C 2 symmetry, with the angle between the least squares planes containing Cu1 and each ligand being 84.14 (8) (Table 3) and the 4 ' parameter being 0.66, and the dmbpy ligands are slightly twisted on the 2,2 0 carbon bond to give an angle of 9.69 (7) between the N1/C1-C5 and N2/C6-C10 rings and 7.97 (8) between the N3/C13-C17 and N4/C18-C22 rings. Moreover, the octahedral coordination environment of Hf1 is also slightly distorted, with Hf1-F bond lengths ranging from 1.9945 (10) to 2.0111 (11) A ˚. Like in compound (I), hydrogenbonding interactions are present between the water molecule of crystallization and fluorine atoms on the trans position of HfF 6
2À anions, but the geometry of the hydrogen bond is slightly different from that in compound (I) [see O1-H1BÁ Á ÁF2 (Table 4)].
In the extended structures of compounds (I) and (II), the [Cu(dmbpy) 2 ] + cations and octahedral MF 6 2À anions are closely packed via Coulombic interactions (Fig. 3). The Á/Ã-[Cu(dmbpy) 2 ] + cations stack into racemic pairs along the caxis direction via a heterochiral face-to-faceinteraction between the N1/C1-C5 and N2/C6-C10 rings with an interplanar angle of 0 , interplanar distances of 3.347 and 3.355 A ˚, and centroid-centroid distances (d py-py ) of 3.6967 (12) and 3.7016 (8) A ˚, for compounds (I) and (II), respectively (Tables 5 and6). Next, Á/Ã-[Cu(dmbpy) 2 ] + pairs pack into racemic chains along the c-axis direction with heterochiral parallel displacedinteractions between the N3/C13-C17 and N4/ C18-C22 rings with an interplanar angle of 0 , interplanar distances of 3.708 and 3.678 A ˚, and centroid-centroid distances (d py-py ) of 5.3726 (13) and 5.3777 (11) A ˚, for compounds (I) and (II), respectively. The MF 6 2À anions with hydrogen-bonded water molecules are interlaced between the racemic chains to form the extended three-dimensional structure. Compared to other molecular compounds with MF 6 2À anions in an extended and complicated hydrogen network (Gautier et al., 2012;Nisbet et al., 2020Nisbet et al., , 2021)), the MF 6 2À anions in (I) and (II) experience less distortion because the hydrogen-bonding contacts are less extensive and only occur along the same axis due to the site symmetry of hydrogen-bonding interactions (Kunz & Brown, 1995;Halasyamani, 2004). Mei et al., 2011). All these structures have distorted tetrahedral [Cu(dmbpy) 2 ] + cations with C 2 symmetry, with a range of the angle between the leastsquares planes containing the metal ion and each ligand being from 75.06 to 86.74 . Moreover, 4 ' parameters for these structures range from 0.70 to 0.74, whereas for both compound (I) and (II) the parameter is 0.66 (Okuniewski et al., 2015). Unlike compound (I) and (II), which have bivalent anions MF 6 2À , the compounds reported in the CSD are chargebalanced by monovalent anions and display two different types of packing architectures distinct from those of the title compounds: [Cu(dmbpy) 2 ][BF 4 ], [Cu(dmbpy) 2 ][PF 6 ], and [Cu(dmbpy) 2 ][ClO 4 ] are isostructural, crystallizing in space group P2 1 /c. Compared to compounds (I) and (II), the ratio of cations-to-anions is smaller in these monovalent-anion compounds. Instead of racemic chains, homochiral chains are observed with homochiral displacedinteractions between the ligands with an interplanar angle of around 30 . No local or extended hydrogen-bond networks are observed because these structures do not contain water molecules of crystallization.
Another type of packing architecture is found in [Cu(dmbpy) 2 ][C 16 H 9 O 8 ]ÁH 2 O
The compounds reported here were synthesized by the hydrothermal pouch method (Harrison et al., 1993). In each reaction, reagents were heat-sealed in Teflon pouches. Groups of six pouches were then placed into a 125 ml Parr autoclave with 45 ml of distilled water as backfill. The autoclave was heated at a rate of 5 K min À1 to 423 K and held at 423 K for 24 h. The autoclaves were allowed to cool to room temperature at a rate of 6 K h À1 . Orangish red solid products were recovered by vacuum filtration with a moderate yield. Compound (I) was synthesized in a pouch containing 0.4195 mmol of CuO, 0.4195 mmol of ZrO 2 , 0.835 mmol of 6,6 0 -dimethyl-2,2 0 -bipyridyl, 0.15 ml (4.14 mmol) of HF (aq) (48%), and0.1 ml (5.5 mmol) of deionized H 2 O
Crystal data, data collection and structure refinement details are summarized in Table 7. Hydrogen-atom positions were assigned from difference map peaks with the exception of the C-H hydrogen atoms of dmbpy, which were constrained to ride at distances of 0.95 A ˚from the associated C atoms with U iso (H) = 1.2U eq (C) within OLEX2 (Dolomanov et al., 2009). The water occupancies in both structures are refined freely. Four reflections showing very poor agreement were omitted from the final refinement for compound (I).
Crystal data
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Hydrogen-bond geometry (Å, º)
Bis[bis(6,6′-dimethyl-2,2′-bipyridine)copper(I)] hexafluoridohafnate(IV) 0.671-hydrate (II)
Crystal data
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.