IntroductionIn previous papers we have described the supramolecular motifs that occur in crystals of metal complexes containing the ligands 2,2′-bipyridine (bipy) and 2,2′:6′,2″-terpyridine (terpy). The preferred motif for complexes [M(bipy)3]z+is the sixfold aryl embrace (6AE) comprised of a concerted cycle of six edge­to­face (EF) primary motifs. The crystal supramolecular motif for these complexes is a linear chain in which each [M(bipy)3]z+forms two 6AEs.1The dominant crystal supramolecular motif for [M(terpy)2]z+and related complexes is a square two­dimensional net in which each complex is involved in four parallel fourfold aryl embraces (P4AE) with neighbouring complexes.2–4This investigation has been extended to metal complexes with the 1,10­phenanthroline (phen) ligand, and in an earlier paper5we reported an investigation and survey of the M(phen)n(n⊕=⊕1, 2, 3) complexes recorded in the Cambridge Structural Database (CSD).6,7Metal complexes of this planar aromatic ligand take part in both EF and OFF primary interactions (seeFig. 1), but with a clear preference for OFF motifs, consistent with the large surface area of the ligand (relative to bipy). The parallel fourfold aryl embrace [P4AE, seeFig. 1(d)] is also a strong feature of crystalline M(phen)2and M(phen)3complexes, as is the double edge­to­face (EF)2[seeFig. 1(c)]. Extended motifs in one and two dimensions are propagated mainly by OFF primary motifs, and one three­dimensional net was identified.5(a) Two views of the offset face­to­face (OFF) interaction, (b) the edge­to­face (EF) interaction between a pair of coordinated phenanthroline ligands, (c) the double edge­to­face, (EF)2, and (d) the parallel fourfold aryl embrace, P4AE, formed between a pair of M(phen)2X complexes (here X⊕=⊕phen).A current experimental program involves the crystallisation of metal complexes containing phen ligands, exploring further the crystal supramolecular motifs. One general objective is to be able to predict crystal packing, and then to design and engineer crystals which incorporate specified packing features. In order to achieve this objective it is necessary to understand the energies of the supramolecular motifs5and to understand the synergies and antagonisms between phen­based motifs and those of other components, and also the competitions between different supramolecular forces. In this paper we consider complexes containing phen ligands and non­bridging oxalate (ox) ligands, and report the crystal structures and packing of three compounds, (Ph4P)[Cr(phen)(ox)2](H2O)1, [Co(phen)2(ox)](BF4)2, and [Co(phen)2(ox)]I(H2O)2(EtOH)0.53. The bidentate oxalate ligand is a hydrogen bond acceptor and can participate in hydrophilic interactions, in contrast to the distinctly hydrophobic character of M(phen)nembraces. Compound1includes only one phen ligand but also a Ph4P+cation, which itself is well known to participate in multiple phenyl embraces which can extend in one, two and three dimensions.8–12Thus these compounds present competing possibilities, which are analysed in this paper.A considerable number of mixed ligand phen–ox metal complexes is known,13,14but the only structures reported with coordinates in the CSD are a diastereomer of [Cr(phen)(ox)2]−,15(Ph4As)[Cr(phen)(ox)2]H2O (reported16while our work was in progress), and [Cu(phen)(ox)(H2O)]H2O.17,18These oxalate complexes are distinct from another well known class in which oxalate bridges generate two­ and three­dimensional nets.19–21