The articles published in the tenth anniversary issue of CrystEngComm are reviewed. The issue highlighted the state-of-the-art of crystal engineering and new trends and developing areas in crystal engineering. In particular, the following article emphasises developments in the areas of intermolecular interactions, notably hydrogen and halogen bonds; metal–organic frameworks or coordination polymers; polymorphism and solvates.

Recent advances in crystal engineering

Compartmental Schiff-base ligands--a rich library of tectons in designing magnetic and luminescent materials.

Molecular magnetism, quo vadis? A historical perspective from a coordination chemist viewpoint☆

Designed materials offer noteworthy applications which are often architecture dependent. Despite knowing such a fact, one of the major challenges faced by the scientific community is to find ways to predict and, if possible, control the resultant architecture of a network. If such an exercise is fruitful, it creates enormous opportunities to synthesize exotic materials with tailor-made applications. Any network is composed of individual molecules and the transition from a single molecule to a network can be achieved through several routes taking advantage of synthetic chemistry. There exists a molecular building block at the heart of such a transition which mediates such a process from a single molecule to a network. Although a large number of building blocks have created assorted materials, utilization of a well-defined coordination complex as the building block (i.e., metalloligand) is unique for the construction of a designed architecture. A coordination complex as the building block offers structural rigidity that places the auxiliary functional groups to a pre-organized conformation. Such auxiliary functional groups could then coordinate a secondary metal ion or be involved in the self-assembly via weak interactions, such as hydrogen bonds. This review focuses on the recent progress achieved through assorted molecular building blocks towards generating ordered networks. Broadly, two classes of metalloligands will be discussed: those offering hydrogen bond sensitive functional groups and those tendering coordination bond responsive groups. Nevertheless, the result is the construction of networks of a highly-ordered nature in both cases. The present review is expected to provide new strategies for constructing functional materials through metalloligands for challenging and practical applications.

Molecularly designed architectures – the metalloligand way

The hydrothermal reaction of M(NO3)2·4H2O (M = Zn and Cd) with benzene-1,4-dicarboxylic acid (H2bdc) or benzene-1,3-dicarboxylic acid (H2ip) and 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) produced the mixed-ligand coordination polymers (MOFs) 3∞{[Zn2(μ2-bdc)2(μ4-btre)]} (1), 3∞{[Cd2(μ4-bdc)(μ4-btre)2](NO3)2·H2O} (2) and 2∞{[Zn2(μ3-ip)2(μ2-btre)(H2O)2]·2H2O} (3). The compounds, characterized by single-crystal X-ray diffraction, X-ray powder diffraction, solid-state cross-polarization (CP) magic-angle-spinning (MAS) 13C NMR and thermoanalysis, feature 3D metal–organic frameworks for 1 and 2 and 2D double layers which are connected through hydrogen bonds from the aqua ligands for 3. The CPMAS 13C NMR spectra picture the symmetry-independent (unique) C atoms and the bdc/ip-to-btre ligand ratio in agreement with the crystal structures. The zinc and cadmium coordination polymers 1–3 show a strong bluish fluorescence upon excitation with UV light (the free btre ligand is non-luminescent).

Crystal structures and solid-state CPMAS 13C NMR correlations in luminescent zinc(II) and cadmium(II) mixed-ligand coordination polymers constructed from 1,2-bis(1,2,4-triazol-4-yl)ethane and benzenedicarboxylate

This paper illustrates the versatility of mono- and heterobinuclear complexes with dissymmetric compartmental ligands in designing molecular and supramolecular heterometallic systems. Mononuclear complexes with side-off bicompartmental ligands derived from o-vanillin act efficiently, through their empty compartment, as hydrogen-bond receptors and as second coordination sphere ligands. These Schiff- bases are also suitable for synthesizing 3d-3d′ and 3d-4f heterobinuclear complexes. Both 3d-3d′ and 3d-4f complexes can be employed as nodes in obtaining coordination polymers with various dimensionalities and network topologies, as well as interesting magnetic and optical properties.

Crystal engineering of hybrid inorganic–organic systems based upon complexes with dissymmetric compartmental ligands

Heterobinuclear [CuIIMnII] and [CuIICoII] cationic complexes can efficiently act as nodes for designing coordination polymers. The crystal structures of two binuclear precursors, [LCuCo(NO3)2] (1) and [LCuMn(NO3)2] (2), have been solved (L2− is the dianion of the Schiff base resulting from the 2 : 1 condensation of 3-methoxysalicyladehyde with 1,3-propanediamine). The nitrato ligands, coordinated to CoII and, respectively, the MnII ions from the precursors, are easily replaced by exo-dentate ligands, resulting in 1-D coordination polymers: 1∞[L(H2O)CuCo(oxy-bbz)]·CH3CN·C2H5OH (3), 1∞[L(H2O)CuCo(2,5-dhtp)]·CH3CN (5) and ∞[L(H2O)CuMn(ox)]·3H2O (6) (oxy-bbz2− = the dianion of 4,4′-oxy-bis(benzoic) acid; 2,5-dhtp2− = the dianion of 2,5-dihydroxy-terephthalic acid; ox2− = the dianion of the oxalic acid). In the case of the [CuMn] node, the interaction with oxy-bbz2− affords a binuclear complex, [LCuMn(oxy-bbz)(H2O)2] (4).

Diana G. Branzea

Papers

Crystal engineering of hybrid inorganic–organic systems based upon complexes with dissymmetric compartmental ligands

New heterometallic coordination polymers constructed from 3d–3d′ binuclear nodes

A 2D Coordination Polymer with Canted Ferromagnetism Constructed from Ferromagnetic (Ni

Crystal Engineering of Hybrid Inorganic—Organic Systems Based Upon Complexes with Dissymmetric Compartmental Ligands