INTERACTION OF METAL IONS WITH HUMIC ACID‐LIKE MODELS. PART 4. SYNTHESIS, SPECTRAL PROPERTIES, AND CRYSTAL AND MOLECULAR STRUCTURE OF TETRAKIS(μ‐2,6‐DIMETHOXYBENZOATO)DIAQUADICOPPER(II) AND OF BIS(μ‐2,6‐DIMETHOXYBENZOATO)BIS(μ‐ACETATO)DIAQUADICOPPER(II), A CASE OF A DIMERIC COPPER(II) CARBOXYLATE CO